Eye of the Storm

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Tuesday, August 30, 2005

Pre-landfall forecast verifications for NHC

Thought I would follow up on my comments from Sunday (on the 12 and 24 hour pre-landfall forecast positions from Charley and Ivan) with how the forecasts fared this time around. 24 hours out, the forecast position for 12Z (7 AM CDT) was 29.1 North 89.6 West. 12 hours out, the forecast was 29.2 N 89.7 W. Actual position was 29.5 North 89.6 West., yielding errors of 24 and 23 nautical miles, respectively.

With the caveat that this certainly may not be representative of overall performance (since it only covers a quarter of the forecasts made over the five days before landfall, here's the rundown for forecasts from 12 to 120 hours before landfall.

12 hours - 29.1N 89.6W 23 nm
24 hours - 29.2N 89.7W 24 nm
36 hours - 29.0N 89.8W 44 nm
48 hours - 28.6N 89.9W 70 nm
72 hours - 29.5N 86.3W 173 nm
96 hours - 30.5N 84.5W 328 nm
120 hours - 29.0N 86.0W 213 nm

And no, there is are no typos in that, the 96 hour forecast really was 54% worse than the 120 hour forecast. Mostly because the 120 hour forecast was 'uncertain' so the track of the extended forecast was just a straight line to the west-northwest. The next day, there was a higher confidence in the scenario of the storm curving to the north-east, and the forecast featured that. Of course, while the general idea was right, the timing of it was way off.

The Katrina graphics archive shows how the forecast track shifted over the life of Katrina.

Personal post

For about as long as I've followed hurricanes, I've always had a bit of an odd feeling after landfall. Something on the order of 'Well, it's out of our hands now', as if forecasters somehow controlled or dropped responsibility for the storm the moment of the center of the eye crossed land. Such was my feeling today.

As I expected, it was a very long drive home (slightly longer than usual time-wise owing to some heavy rain encountered, but otherwise long in the sense that my mind was heavily burdened). When I pulled onto I-10, I saw in my rear-view mirror the site all too familiar from last year, a large convoy of the trucks used to aid workers in restoring electricity to storm-stricken areas bound for their staging area.

Had dinner at a friend's apartment and then drove to my own. Too impatient and tired to properly navigate the close confines of my complex's parking lot, I rounded my car into the rear bumper of a truck, putting a nice dent just behind the passenger door.

Didn't care to watch any of the media coverage of landfall. I'm not sure of a major landfall that the full scope of damage was comprehensively covered in the first few hours after. This goes back as far as Andrew and as recently as Dennis. The bigger the storm, the more inaccurate the initial read.

At the moment, the death toll from Katrina is the greatest U.S. death toll from a hurricane since Agnes of '72, which claimed 117 lives, almost all of them lost in epic flooding that occurred after the remants of the storm sat over Pennsylvania for more than a day. The deadliest prior to that was Camille, which caused 256 deaths. Nearly half of those (113) were from flooding caused by remnants.

Sunday, August 28, 2005

Katrina continues to intensify

Last post from Orlando. Next will be from Tallahassee in a few hours, pending computer availability. Brendan Loy should be up and blogging again soon.

Pressure is now down to 902 millibars.

Model guidance for intensity is not encouraging. Latest SHIPS output is for 180 mph winds in 12 hours with no indication of weakening before landfall (note that DSHP is the SHIPS output with the dissipative effects of land taken into account.)

The 12Z runs of GFS, GFDL and NOGAPS models do not provide much hope for New Orleans .

I have a feeling that regardless of traffic, the drive to Tallahassee is going to be the longest ever for me. Work has helped me somewhat in keeping my thoughts off the imminent catastrophe, but I won't have any such distraction on the road.

Katrina's winds now at 175 mph


At 10 AM CDT, the center of category five Hurricane Katrina was at 26.0 North 88.1 West, 225 miles south-southeast of the mouth of the Mississippi River. Maximum sustained winds are 175 mph and minimum central pressure is 907 millibars (26.78"). Hurricane force winds extend up to 105 miles from the center.

Hurricane Katrina Advisory Number 23

"Katrina is comparable in intensity to Hurricane Camille of 1969 only bigger." Fluctuations in strength are likely, however, "we see no obvious large-scale effects to cause a substantial weakening (of) the system and it is expected that the hurricane will be of category 4 or 5 intensity when it reaches the coast".

There is no change in the track forecast, which is in the center of model guidance. Due to the average errors in a 24 hour forecast, Katrina could strike anywhere from southeastern Louisana to the Missippi coast. Destructive weather extends well beyond the eye, so focusing on the exact point of landfall is not necessarily productive.

Hurricane force winds are expected to last for up to 150 nautical miles (172.5 statute miles inland)

Hurricane Katrina Discussion Number 23

Official track forecast with warning areas

Alternate view of track forecast


A couple of days ago, I wrote about the average track error in the NHC's forecasts last year. I went back and looked at the forecasts for the two hurricanes last year that featured a synoptic situation roughly similar to this, namely Charley and Ivan.

In the case of Charely, the forecast that took place 24 hours before landfall was off by about 40 nautical miles and the forecast 12 hours before was off by 29 nautical miles. Both were too far to the left, meaning that Charley turned harder than forecast.

For Ivan, the error at 24 hours out was 42 nautical miles, and the 12 hour error was 26 nm. Again, the forecast was too far left as it hit further east than forecast.

If a similar error to occur in this case, then the resulting landfall position would be comparable to that of Camille. However, due to the greater size of Katrina, effects in New Orleans would be worse than they were for Camille.

No guarantees however, as if we will see a repeat of this type of error. After all, it is quite possible that the forecaster has already factored it into his forecast (i.e. shifted it say, 20 miles to the right of where he normally placed it).

The Gulfstram-IV jet flew this morning to feed upper-air data from the Gulf of Mexico to the 12Z global models, which just started crunching the numbers. Forecasts will be coming out from them over the next two hours, and any changes in their tracks would affect a change in the 5 PM advisory package.

Intensity forecasting at this stage is nothing more than speculation with regards to whether Katrina will maintain her strength. It is fairly certain however, that if she were to weaken some, the bottom would probably be at the high end of the category four range (i.e. 145-155 mph winds).

If you are under evacuation orders now is the time to leave. Time for preparations to secure property is expiring. Remaining in your present location longer reduces your chances of making it to a shelter or other refuge in a safe manner. Conditions will quickly detoriate this evening.

Is Katrina an annular hurricane?

One thing frequently mentioned in discussion from the NHC about intense hurricanes is that they are prone to fluctuations in intensity such that category five strength is not held for a long period of time. The exception to this is a special classification called an anular hurricane. Such hurricanes do not fluctuate as rapidly. The most recent case was Ivan, which retained category five status for 30 consecutive hours.

The tell-tale sign of an annular hurricane is that the convection is uniform, making a perfect circle, i.e. there are no spiraling bands, just a donut. That is almost exactly the case with Katrina, as one can see from infrared satellite. Another feature is a larger than average eye (average being 14 miles). The message from the recon plane shown in my last full update shows that Katrina's eye is 25 nautical miles in diameter, so it is well above average. As far as conditions associated with annular hurricanes go, some of the conditions are most certainly there. Average Sea Surface Temperatures associated with them are 26.9° C. Katrina is certainly on the more favorable side of that (ref). Weak vertical wind shear is another key factor. That is certainly the case in the immdiate vicinity of Katrina(ref)

For a technical paper on annular hurricanes, see the paper 'Annular Hurricanes' (PDF) by John Knaff, James Kossin and Mark DeMaria (Demaria, by the way developed the Statistical Hurricane Intensity Prediction Scheme (SHIPS) that has been mentioned so much with regards to the potential intensity of storms.

It will be over the head of most people, but it is worth checking out to compare the satellite imagery of known annular hurricanes with that of Katrina.


So enough of the theory, what does this mean practically?

It means that the situation has gotten even worse. If Katrina is indeed annular, then the chances of her retreating down to say category three status are nil. If we make the somewhat unlikely presumption that she has reached her maximum strength (and again if she is annular), then the averages of such hurricanes suggest that she would only weaken to 145 mph at landfall. That would be a storm with Charley-like intensity, but on a much larger scale as Charley was puny compared to the present size of Katrina.

I do hate repeating myself when it comes to evacuating, but the only way I've been thinking of not repeating myself involves a very salty string of compound-complex expletives that would not be appropriate for this family publication.

If you are on the coast, or in a low-lying area, or otherwise in a structure of dubious integrity, and are in the cone of uncertainty, you need to leave now. Otherwise, you will become a statistic.

One last thing to share: In my high school earth science class, my teacher stated 'There is only one tool needed for disaster recovery from a category five hurricane: A bulldozer".

Category Five Katrina

WTNT62 KNHC 281117



Hurricane Katrina Update 280400 CDT

At 4 AM CDT, the center of extremely dangerous Hurricane Katrina was at 25.4 North 87.4 West, 275 miles south-southeast of the mouth of the Mississippi River and moving to the west-northwest at 10 mph with a turn to the northwest. Winds are up to 145 mph and minimum central pressure is 935 millibars (27.61")

Hurricane Katrina Advisory Number 21

Katrina continues to both strengthen and grow in size. While the official forecast does not call for a further increase in size, it is possible. The Statisical Hurricane Intensity Prediction Scheme does call for Katrina to make category five before landfall, however the official forecast goes just short of that (155 mph) due to the unpredictable nature of structural changes of the eye that would weaken Katrina temporarily. While the specifics are unknown exactly, it is clear that Katrina will be a very dangerous hurricane at landfall.

Katrina is moving along as forecast. Models are in tight agreement and their consensus has barely shifted from their past run. As such, the track forecast is merely an update of the previous one (i.e. the only thing that changed was the initial position).

Hurricane Katrina Discussion Number 21

Official forecast track with watches and warnings


Here is the model guidance, which is nearly unaminous in putting New Orleans in the bullseye. The only deviator being the North American Model (NAM, labeled ETA1 in this graphic); it is a hemispheric model that does not exhibit much skill in tropical cyclone forecasting.

So, those who went to bed thinking that the storm would either not strengthen or would deviate from forecast 'like it always does' are facing reality this morning. An extremely dangerous hurricane is taking the worst possible path.

If you are in New Orleans, you should leave now. Going west is the preferable option, with north being a viable one as well. Note that it doesn't have to be particularly far west as the worst effects of the storm are on the eastern side of it. People in coastal areas east of the center line should head inland by proceeding north.

In New Orleans, traffic is liable to be bad enough to justify leaving now, rather than spending time to secure property. In any event conditions will start to rapidly detoriate tonight, so the absolute latest one could plausibly hit the road in a safe manner would be early afternoon.

One note on the possibility of Katrina weakening due to an eyewall replacement cycle. Weakening is a relative term. If we were talking about a category three storm, then weakening from an ERC does reduce the hurricane's winds to those that are not particularly damaging. However, when we are talking about a category five or a strong category four as we are with Katrina, an ERC is only going to knock her down to category three. Category threes are still dangerous and destructive storms. It would not create catostrophic damage in New Orleans, but damage would still be major.

Looking at the Tropical Cyclone Heat Potential chart, I notice that Katrina is yet made her way across the hot spot yet.

Cutting this short and here's why:

URNT12 KNHC 281120
A. 28/11:04:10Z
B. 25 deg 39 min N 087 deg 32 min W
C. 700 mb 2310 m
D. NA kt
E. deg nm
F. 141 deg 153 kt
G. 046 deg 018 nm
H. 910 mb
I. 10 C/ 3056 m
J. 25 C/ 3057 m
M. C25
N. 12345/ 7
O. 1 / 1 nm
P. AF302 1712A KATRINA OB 10MAX FL WIND 153 KT NE QUAD 10:58:50 Z

That is a report from the recon plane. Pressure has plummeted. Katrina has gone category five.

Hurricane Katrina Update 0100 CDT

At 1 AM CDT , the center of extremely dangerous Hurricane Katrina was at 25.1 North 86.8 West, 310 miles south-southeast of the Mississippi River and moving to the west-northwest at 8 mph with a turn to the northwest expected later today. Maximum sustained winds are up to 145 mph, which makes Katrina a category four on the Saffir Simpson-scale. Minimum central pressure has fallen to 935 millibars (27.61"). Hurricane force winds extend up to 70 miles from the center and rains from the storm will start to affect the gulf coast on Sunday evening.

Hurricane Katrina Special Advisory Number 20


Hurricane Katrina Special Discussion Number 20

Bedtime. Up at 5 (EDT).

Saturday, August 27, 2005

Hurricane Katrina Update 280300Z


At 10 PM CDT, the center of dangerous Hurricane Katrina was at 25.0 North 86.2 West, 335 miles south-southeast of the mouth of the Mississippi River and moving to the west-northwest at 7 mph with a turn to the northwest expected to begin on Sunday. Maximum sustained winds are 115 mph and minimum central pressure has fallen to 939 millibars (27.73").

Hurricane Katrina Advisory Number 19

While maximum winds are unchanged, the wind field has increased in size. Enviromental conditions are favorable for intensification. Changes in the structure of Katrina could alter her strength, but they are not possible forecast with our present knowledge of hurricanes; they can only be reported as they happen. "The bottom line is that Katrina is expected to be an intense and dangerous hurricane heading towards the northern Gulf coast and this has to be taken very seriously."

It appears that the anticipated turn to the northwest has begun due to the retreating upper-level ridge of high pressure. The offical forecast closely follows the consensus of the global forecast models.

Hurricane Katrina Discussion Number 19

Official forecast track with watch and warning areas


As Brendan notes, traffic is light in New Orleans. Tomorrow will probably feature the worst traffic in the history of the city. Plan and take action accordingly.

The most recent report from the Hurricane Hunters indicated that the eyewall is still ragged. However, pressure continues to fall, so while setup for the next round of intensification is not quite in place, it is near. Also, as noted in the discussion, Katrina is beginning to hog the Gulf of Mexico as she has expanded in size over the past few hours. Clouds from Katrina now extend from Belize to the edge of the Florida panhandle.

Several years ago I spoke to my high school principal about the then recent F5 tornado that struck Jarrell Texas , killing 27 people and leveling an entire subdivision of houses. I made a comment to the effect that things like that that make you realize that while we think we are the biggest and baddest thing around that there is something far bigger than us out there. He nodded and alluded to the MC Hammer song 'Pray' ("that's we pray".)

And such is the situation is tonight. While the traditional worst case refence for a hurricane is Camille, the potential path of Katrina makes me reach further back for such a reference, 105 years to be specific. I am referring, of course, to the Galveston storm of 1900. If Katrina bears on New Orleans, that is the sort of devestation we will see. While the death toll need not be high, inaction by individuals and the government could lead to that.

Pray for last minute shear, pray for an ever so slight delay in the sharpening of the turn to the north south that Katrina heads towards the less populated areas of the coast.

Hurricane Katrina Update 272100Z



At 4 PM CDT, the center of dangerous Hurricane Katrina was at 24.6 North 85.6 West, 380 miles southeast of the mouth of the Mississippi River and moving to the west at 7 mph. Maximum sustained winds are 115 mph and minimum central pressure is 945 millibars (27.91").

Hurricane Katrina Advisory Number 18

Katrina remains in an eyewall replacement cycle, with one eye 9 nautical miles in diameter and the other about 50 nautical miles wide. The pressure has started to fall agin after maxxing out at 950 millibars. Katrina remains south of a ridge that is located over the northern gulf coast. Over the next 24 hours that ridge is expected to weaken, and cause Katrina to turn to the north. Some models have shifted their tracks, but have not done so in a uniform manner (and remain in general agreement on the forecast), so the offical forecast track is only slightly changed to feature a slight nudge to the west. Katrina is expected to strengthen once her eyewall replacement cycle is complete. Official forecast calls for 145 mph winds at landfall while model guidance is more agressive, calling for 150 mph winds. It is possible that Katrina could become a category five, it is also possible that there will be an eyewall replacement cycle intervening that would cut her intensity short of what is forecast.

Hurricane Katrina Discussion Number 18

Official forecast track


Last night I drove to Orlando so that I could perform my one weekend per month of duty for the Naval Reserves. As such, I haven't had the opportunity to see much of the storm today.

However, I do have some two storm related stories to offer that are Navy related.

Yesterday, the 600 sailors and officers of the frigates Stephen W. Groves and John L. Hall left Pascagoula Mississippi to evade Hurricane Katrina. Moving ships on short notice is a non-trivial event that is not done for fun. It is only done when a serious threat exists.

Two members of my unit were in New Orleans on the first of their two weeks of Active Training. Careful readers will note the use of past tense in the previous sentence. They are back in Florida after being told yesterday to get out of town on the first flight they could get tickets for.

The Navy is taking this seriously. So should all other residents of the northern Gulf coast.

If you were writing a book on hurricanes and wanted to get examples of the factors needed to create a category five hurricane, you would not have to search hard. For all exist right now. Low shear? Doesn't get lower than this (parts of Katrina are in areas of sub-5 knot shear). High amounts of heat potential? Red freaking hot, right in the middle of Katrina's path. A well-organized, already powerful hurricane? Here you go.

Can I guarantee a category five? No. Is Katrina going to try her damndest to make it? Yes. The only things limiting her are space, time and the sole weakness of a powerful hurricane: An unpredictable eyewall replacement cycle that temporarily reduces its strength.

If you are living on the coast or an otherwise low-lying area inside the danger cone portrayed in the National Hurricane Center forecast and you do not have plans to leave, then you are putting your life in grave danger.

The forecasters of the National Hurricane Center have pursued their difficult education, worked the long hours, and use every last bit of brain power to make their forecasts to save lives and mitigate property loss. To disregard them is to dishonor their work.

There is still time to secure life and property, but it is quickly running out. For the residents of the northern gulf coast, now is the time to take decisive action to do both.

Friday, August 26, 2005

Hurricane Katrina Update 270300Z

At 11 PM EDT, the center of Hurricane Katrina was at 24.6 North 83.6 West, 460 miles southeast of the Mississippi River and headed to the west-southwest at 8 mph. Maximum sustained winds are an estimated 105 mph and minimum central pressure is estimated to be 965 millibars (28.50").

Hurricane Katrina Advisory Number 15

Katrina's appearance on satellite continues to improve as Katrina is taking on a text-book appearance. Two of the three agencies that provide intensity estimates estimated a wind speed of 104 mph, so the intensity is set at 105 mph. A recon plane will be flying into the hurricane later tonight. Conditions are extremely favorable for intensification and the intensity forecast brings Katrina to category four strength (130 mph) winds, but this is lower than being suggested by the FSU Superensemble, which brings Katrina's winds up to 150 mph before landfall.

Katrina continues to move to the southwest. Data from the upper-air surveillance jet suggests that the high continues to be very strong. However, a weakness is expected to form in it that will allow a turn to the north, allowing Katrina to find her way to the northern coast of the Gulf of Mexico in 48 hours or so. Computer model guidance is tightly clustered, which boosts the forecaster's confidence in his prediction.

Hurricane Katrina Discussion Number 15

Official forecast track


Residents of coastal southeast Louisana, Missippi, and western Alabama need to start taking action tomorrow morning to prepare for the arrival of what will be a dangerous hurricane. Due to the warming of the Gulf of Mexico that has taken place throughout the summer, there is far more fuel for the hurricane as it approaches the coast. Dennis ran out of gas as it were during his last hours ashore. This is much less likely to be the case for Katrina as deep warm waters extend almost all the way to land.

At 5 PM EDT, the center of Hurricane Katrina was at 24.8 North 82.9 West, 70 miles west-northwest of Key West. Maximum sustained winds remain near 100 mph and minimum central pressure is down to 965 millibars (28.50").

Hurricane Katrina Advisory Number 14

Despite the recent drops in pressure, recon has not found flight level winds that would suggest anything greater than 100 mph winds at the surface. The fact that the eyewall is not entirely closed may be the reason why winds are a bit lower than the pressure would normally suggest.

Katrina remains caught between steering flows that are pushing her south. Both sources of that are expected to weaken over the next 24 hours, causing Katrina to turn to the west. The models are in general agreement on the movement of a trough that will come from the northwest of the high pressure ridge that will act to open up a path for Katrina to turn north. The result of the better agreement of the models on the scenario caused the official track forecast to be shifted to the west by 150 nautical miles (172.5 statute miles). With projected landfall still 72 hours away, further modifications to the forecast track are possible.

Katrina is expected to move over an area of exceptionally warm (and deep) water. That combined with favorable upper-air conditions should allow Katrina to reach category four status before landfall. The intensity forecast is in line with the output of the SHIPS and GFDL models, but under that of the FSU Superensemble, which brings Katrina's winds up to 150 mph strength prior to landfall.

Hurricane Katrina Discussion Number 14

Official forecast track


A very difficult move to make, but probably the right one. The National Hurricane Center really does not like to make these kinds of jumps in their forecast, but the unaminous shift in the forecast models combined with Katrina's continued movement to the west-southwest left them little choice.

The only direct comment I have on the forecast has to do with intensity. After looking at the water vapor loop, I realized dry air could serve to keep Irene from doing dramatic rapid intensification. Right now there is dry air immediately to her north and there looks to be a pocket of it being pushed south through the southeastern U.S. and will ultimately end up in Katrina's path. (In these imagery, dry air is black, while increasingly bright shades of gray indicate moisture). It may not amount to much, Katrina probably will still manage to make category four status. However, if she doesn't then dry air will probably be the reason why.

Brendan Loy has a post about the peril that New Orleans may be in and the difficult problems of the track forecast and evacuation orders. It is indeed a difficult problem.

The forecasting of the tracks of hurricanes is much more accurate than in the past and overall improves every year. However, we are still far from being able to give the kind of precision and certainty that would alleviate the emergency planner's fear of a false alarm.

The problem in New Orleans is that it is generally accepted that the city requires 72 hours notice to be properly evacuated. In 2004, a great year for the accuracy of hurricane forecasts relative to the historical average, the average track error of a 72 hour forecast was 150 nautical miles. Given that error, a forecast that has a hurricane striking east of Mobile in 72 hours(well enough away to not be of worry to New Orleans if it were indeed to strike there), still has enough error that New Orleans is inside the zone of uncertainty.

Even at a short period the uncertainty can be greater than would be desired by planners. In 2004 the average forecast error at 12 hours was 33 nautical miles. Now this sounds small but in practical terms it is somewhat large. Consider that in 1969, when the monsterous Hurricane Camille passed New Orleans to the east by about 40 nautical miles the damage to New Orleans was trivial compared to what it would have been had it come in 30 miles closer. The difference between absolute disaster, major damage (like Betsy of '65) or annoyance is within the margin of forecast error at 12 hours.

As much as forecasters would like to, they can't give the assurances that emergency planners would like.

Hurricane Katrina Update 261800Z

At 2 PM EDT, the center of Hurricane Katrina was at 24.9 North 82.6 West, 60 miles west of Key west Florida and moving to the west-southwest at 8 mph. Maximum sustained winds remain 100 mph and minimum central pressure is down to 969 millibars (28.61").

Hurricane Katrina Intermediate Advisory Number 13A


Every global model plus the GFDL shifted its track to the west its forecast to the west in its 12Z run. Forecasts are now in a fairly tight cluster between eastern Louisana and Mississippi.

While it is generally unwise to hop onto one run of the models as the gospel, it is meaningful when every model makes the same type of shift.

This definitely shifts the area of concern much further west than I had been figuring. Shreds my forecast track thinking as well as that of the NHC (although, of course they were more conservative than me and had eastern Louisana at the edge of the zone of uncertainty in their 11 AM forecast).

I had a clue that my thinking was bad right after the 11AM update, when I had the novel idea of looking at storm history (sarcasm here, as this is something fundamental that I should have been doing all along).

Storms that go through south Florida on the type of path that Katrina has taken just don't make sharp turns into the Panhandle. The ones that go through the Keys to hit the Panhandle were on a northwesterly type course to begin with.

Hurricane #6 of 1935, which featured an erratic track to begin with, is the only example in storm history of a sharp turn from the sort of path Katrina has taken.

More reasonable are the tracks of Andrew and Betsy of 1965.

It is hard to argue against history. While there are no guarantees of an exact match in ultimate landfall, it is clear that storms headed west through the Keys just don't turn that sharply. Because of that alone it is reasonable to adjust landfall forecasts to the west. Even moreso given the shift in the models.

As I had been saying earlier, the more west Katrina goes, the stronger she will become. Category four strength at landfall is very likely if the consensus track forecast of the models is correct.

Hopefully the television stations of the Gulf Coast will put their viewers on notice so that they do not go into the weekend not realizing what Monday will bring.

Hurricane Katrina Update 261500Z

At 11 AM EDT, the center of Hurricane Katrina was at 25.1 North 82.2 West, 45 miles northwest of Key West Florida and moving to the west at 7 mph. Maximum sustained winds are up to 80 mph (now significantly stronger, see update below) and minimum central pressure is down to 981 millibars (28.97") (now lower, see discussion).

Hurricane Katrina Advisory Number 12

Recon just found pressure of 971 millibars. Winds observed by doppler radar suggest a surface wind of 85 mph (the recon plane has only sampled the northwest quadrant thus far, finding flight level winds that suggest 80 mph at the surface).

Katrina continues to move south of west. That is expected to flatten to a due west motion during the next 12 hours. Model guidance is widely split on the timing of the erosion of the high pressure ridge that is currently dictating Katrina's westward movement. The 06Z run of the NOGAPS model shifted its forecast landfall position to Louisana (the GFDN model also shows a LA landfall, but it has been on the western outlier for most of the duration of Katrina). The balance of the models take Katrina over the northeastern Gulf coast. Strengthening to a category three is forecast. A special advisory and forecast is now being drafted to cover the lower pressure found by recon.

Hurricane Katrina Discussion Number 12

Official track forecast

I had been expecting Katrina to react favorably to the Gulf of Mexico, so the stronger than expected winds and lower than expected pressure is not a huge shock, but it is a small surprise nonetheless.

I had been expecting a category three with a chance of a category four for the second landfall. The jump that Katrina has gotten on re-intensification makes me think a strong category three to a minimal category four (130-140 mph winds) will be making landfall.

My unofficial watch area continues to be from Mobile Alabama to St Mark's Florida. My warning area is adjusted westward to run from Destin to Mexico Beach Florida. As mentioned in my last update, coastal areas west of my warning area are more likely to receive effects of Katrina than areas inland, while the opposite is true for areas east of my warning area.

Tropical Cyclone Heat Potential
is greater now than it was in when Dennis made landfall
so weakening before landfall will be less significant than it was for Dennis.

Start preparing Florida panhandle, Katrina is heading your way and she's going to be carrying a strong punch.

SLIGHTLY LATER: Dropsonde from the recon plane in the eyewall recorded 95 knots at 925 millibars, which suggests 100 mph winds at the surface... which caused a Special Advisory to be released showing this and the new pressure. Intensity forecast adjusted to show winds in the vicinity of 125 mph at landfall.

The intensity estimate dervied from the dropsonde may be too high. Dropsondes do not record sustained winds, but rather instanteous winds, so it is quite possible that it recorded a gust. Flight level winds at the time suggest that 80 knots/90 mph is more likely. However, the forecaster may be assuming stronger winds will be found in the northeast quadrant. We shall see.

A BIT MORE LATER: The discussion argues the pressure reading of 971 millibars supports 88 knots, hence 85 knots for this advisory. A valid argument, but not one that all forecasters would agree to. Flight level winds will support 100 mph at some point this afternoon, but it may be a while. (Tied into this is the problem associated with having the official forecasts being in knots (converted to mph for the sake of the general public); because the possible values are in increment values, you can have 80 knots or 85 knots, which amounts to 90 or 100 mph. A value of 95 mph is not possible).

Hurricane Katrina Update 260700Z

At 5 AM EDT, the center of Hurricane Katrina was at 25.3 North 81.5 West, 50 miles north-northeast of Key West Florida and moving to the west at 5 mph. Maximum sustained winds are estimated to be 75 mph and minimum central pressure is an estimated 987 millibars (29.15").

Hurricane Katrina Advisory Number 11

Because of the path it took over Florida, Katrina did not weaken much. The center crossed the coast at about 1:30 AM EDT and entered the warm waters of the Gulf of Mexico. While doppler radar only indicates winds of 70 mph, the estimates of the three agencies that analyze satellite imagery were a unaminous 75 mph.

Radar indicates that Katrina is moving nearly due west now (heading 260° at 4 knots). Model guidance shifted west and the official track forecast is shifted west-ward accordingly.

"All inidications are that Katrina will be a dangerous hurricane in the northeastern Gulf of Mexico in the next couple of days." Atmospheric conditions are only expected to become more favorable for Katrina. The official forecast (with winds at landfall of 105 mph) is close to the guidance provided by the Statistical Hurricane Intensity Prediction Scheme (SHIPS). However, this is conservative given that the GFDL and GFDN models forecast a major hurricane.

Hurricane Katrina Discussion Number 11

Official track forecast


It appears that the flight that was scheduled to go into Katrina this morning was scratched at the time Katrina went ashore under the presumption that she would still be overland at this time. It is not clear when the next mission will be as the operations Plan of the Day does not show a recon flight until late tonight. Hopefully, there is room for improvisation in the plan.

My unofficial watch area continues to extend from Mobile, AL to St Marks, FL with the warning area running from Panama City Beach to Appalachicola. It may be necessary to shift my warning area westward later today (to include Destin/Fort Walton area) but I'll hold it as is for the time being. Inland areas east of Appalachicola are likely to receive more of the effects of Katrina than coastal areas while the reverse is true for areas west of PCB. Motion is a little bit slower than I had anticipated when I laid out my preparation time-table, meaning that time of landfall is more likely to occur Monday morning than on Sunday. To some extent that buys residents a little bit of watching and waiting time, but not much. It still would be prudent to go ahead and start making preliminary preparations today (such as having a full tank of gas in the car). Also it doesn't necessarily hurt to go supply shopping today only to find out that the storm will go in to the east or well to the west of your location. After all, there is still a long ways to go in this hurricane season; the supplies purchased could very well come in handy not much later.

I continue to anticipate a category three storm due to the apparant lack of factors that would inhibit intensification (other than space and time;if Irene gives herself more of both by continuing to push further south and west before turning north, then she could creep into category four status prior to landfall).

Katrina goes 'feet wet' -- 260500Z Update

At 1 AM EDT, the center of Tropical Storm Katrina was at 25.4 North 81.1 West, 40 miles southwest of Marco Island, 60 miles northeast of Key West and moving to the southwest at 8 mph. Maximum sustained winds are 70 mph and minimum central pressure is 990 millibars (29.23 ").

Katrina Intermediate Advisory Number 10A

Key West radar indicates that the eye has started to go over water. This event is about 7 hours ahead of the forecast that the NHC put out at 5 PM and it is also further south than anticipated.

Recon plane is scheduled to launch in about half an hour. I don't think it will get to the storm in time for the 3 AM update, but will definitely be there such that the 5 AM intensity will be based off the plane's observations. Because of this, I expect the 3 AM update to carry the Tropical Storm designation for Katrina. I would not be surprised if the 5 AM advisory package has Katrina as a hurricane once again, though land may have taken a bit more of a bite out of Katrina than radar shows, so I'm not confident enough to call that a certainty.

Output from the global forecast models are starting to roll in. GFS is showing a landfall in vicinity of Destin. Some may remember that its forecasts had been significantly further east than most other models. The Canadian model has a similar landfall location, but with slightly quicker timing. 5 AM advisory package will probably feature some sort of west-ward shift in track as a result of Katrina's continued southwesterly movement as well as the shift in these two models, which for most of Katrina's life have been on the eastern edge of the guidance envelope.

Thursday, August 25, 2005

Hurricane Katrina Update 260300Z

At 11 PM EDT the center of Hurricane Katrina was at 25.5 North 80.7 West, 35 miles southwest of Miami, 20 miles northwest of Homestead and moving to the southwest at 8 mph. Maximum sustained winds are 75 mph and minimum central pressure is 984 millibars ( 29.06").

Hurricane Katrina Advisory Number 10

Katrina came ashore at 6:30 EDT and has moved southwest across Dade County since then. Miami National Weather Service recorded a pressure of 984.5 millibars in the eye of Katrina. Some weakening is expected during Katrina's remaining time over land, but strengthening will resume once she finds the Gulf of Mexico. Model guidance now brings Katrina to category three strength.

The southwest motion that Katrina currently has was forecast by the GFDL model. Katrina continues to move along the edge of the upper level high pressure ridge. A weakness in that ridge is expected that will allow a northerly motion in 36-48 hours.

"All indications are that Katrina will be a dangerous hurricane in the northeastern Gulf of Mexico in about 3 days".

Hurricane Katrina Discussion Number 10

Official track forecast


Reports indicate that about one million people are without power in Dade, Broward, and Palm Beach counties. As forecast, rain totals are going to exceed a foot in some areas with the Kendall/Cutler Ridge/southwest Miami areas bearing the heaviest of the load.


More than four hours over land and STILL a hurricane. Remarkable.

Official track forecast was shifted a bit west, mostly due to the southwesterly motion that Katrina has taken (not the result of new model guidance). The global forecast models are crunching numbers now and their results will be coming in over the next few hours, giving the NHC forecasters a little bit of time to examine them before preparing the 5 AM forecast.

I know I am sounding like a broken record, but this more southerly course is bad. Besides the shorter distance, it is also more favorable in terms of terrain. There are two dissapative effects of land with regards to hurricane strength. One is that the storm is not over water, the source of its energy. The other is friction from land, especially that of buildings. Katrina's southerly course is taking her over the Everglades. The difference between the Everglades and open water is slight.

Sea Surface Temperature analysis shows 90° waters in the Gulf of Mexico, warmer than anything Katrina has seen so far. Situation would become even more favorable for Katrina if she gets past 83° West or so, because the warm waters extend deeper, as indicated by Tropical Cyclone Heat Potential Analysis (brighter colors are better for Katrina, worse for residents of the Gulf coast).

I wish I could say that I see inhibiting factors that would limit Katrina's intensification. Unfortunately, the only ones I see are space and time, both of which are just plentiful enough for Katrina to become a dangerous threat to the Florida panhandle.

My unofficial watch area remains Mobile to St Marks, with special concern for Panama City Beach to Appalachicola. Residents in those areas should begin tomorrow preparations for a strong category three hurricane and have those completions complete by Sunday afternoon. My advice is to do all shopping tomorrow, do your at home work on Saturday, and be either gone (if you're in an evacuation zone) or done with preparations on Sunday morning.

I will be have a post at the time that the 5 AM advisory package comes out with the latest thinking on the future path of Katrina as she enters the Gulf of Mexico.

Hurricane Katrina Update 260100Z


At 9 PM EDT, the center of Hurricane Katrina was at 25.8 North 80.4 west, just northwest of the Miami National Weather Service Office and the National Hurricane center, moving south of due west at 6 mph. Maximum sustained winds are 80 mph and minimum central pressure is 984 millibars (29.06").

Hurricane Katrina Intermediate Advisory Number 9B

Florida Cracker has a rolling Katrina update post going, with a generous offering of links to others blogging much nearer to the storm than I am.

As she links, two people are dead from Katrina already. A cold reminder that it does not take a major hurricane to cause fatalities.

I am definitely discomforted from the observations from the Miami NWS as well as with the path Katrina is taking. Re-analysis from Hurricane Andrew showed that Andrew actually continued to intensify shortly after making landfall before weakening inland. With NWS Miami recording a pressure of 985 millibars (compared to the last observation of recon of 986 millibars) Katrina may have pulled off the same trick.

The track is worrisome, because it is a 'short-cut' track. Because of how the peninsula narrows, moving south of west gives Katrina less time over land than if she had moved due west. Less time over land equals less weakening equals more strengthening once she reaches the Gulf of Mexico. It is fortunate for residents of southern Florida in points north and west of Miami, but it will cause increased pain for panhandle residents in a few days.

SLIGHTLY LATER: Definitely concur with this from the NWS Miami Special Weather Statement


Hurricane Katrina Goes Ashore -- 252300Z update


At 7 PM EDT, the center of Hurricane Katrina was at 25.9 North 80.1 West, located on the coast between Hallandale Beach and Miami Beach. Movement is to the west at 6 mph. Maximum sustained winds are up to 80 mph and minimum central pressure is down to 985 millibars ( 29.09").

Hurricane Katrina Intermediate Advisory Number 9A

Selected comments from the 5 PM discussion, not the full synopsis since some of the commments are overtaken by events:

Katrina is expected to move slightly south of due west for the next 12 hours. The ridge that currently lies to the north of Katrina and is dictating her current motion is expected to be partially eroded, which would cause the hurricane to turn to the north after 48 hours. As has been the case for the past couple of days, the models diverge after that. The GFS model continues to be the eastern-most of the bunch, featuring a sharp northeast turn that brings the storm back ashore in the vicinity of Yankeetown (more or less the point where panhandle meets peninsula). The GFDL and GFDN models represent the western edge of the spectrum as they bring Katrina ashore in Alabama and Louisiana respectively. Given the GFDL's and GFDN's poor performance in the recent short term, their forecasts are given less weight, a result of that is the official track forecast being east of the model consensus.

Once Katrina returns to the Gulf of Mexico, conditions are expected to be favorable for re-strengthening. The official forecast brings Katrina to 105 mph winds by time of the second landfall.

Hurricane Katrina Discussion Number 9

Official Forecast track


In a mixed blessing for Florida, Katrina is taking a short-cut track across the southern Peninsula. The track should slightly reduce rain-fall totals in the populated areas of the west coast. The downside from the track is that allows Katrina to hold more of her strength before re-entering the Gulf of Mexico.

The 5 PM intensity forecast is in line with the concerns I have been expressing for a significant hurricane to affect the Panhandle. My area of concern continues to extend from Mobile to St Marks, with the area of highest concern extending from Panama City Beach to Appalachicola.

Residents in those areas should be considering their preparations for a strong category two hurricane. If Katrina heads further west, enabling her to get west of my high concern area, then she will be able to intensify beyond that to a category three storm like Dennis.

For coastal residents of the Panhandle, plan for a 'working weekend' as all preparations should be completed by Sunday afternoon. Given the fragility of electrical power, it would be a good idea to beat the rush and do your battery/flashlight/food shopping tomorrow. After all, despite Dennis making landfall in Pensacola, power was lost in Tallahasse.

As I've mentioned in a previous post, there are two upper-air 'surveillance' flights going on that are collecting observations for the computer models' forecasts tonight. The results of those forecasts will be reflected in tomorrow morning's 5 AM advisory package.

Tropical Storm Katrina Update 251900Z

At 3 PM EDT, the center of Tropical Storm Katrina was at 26.2 North 79.6 West, 35 miles east-southeast of Fort Lauderdale and 35 miles east of Boca Raton. Movement is to the west at 6 mph and is expected to slow during the next 24 hours. Maximum sustained winds are up to 70 mph and Katrina is expected to become a hurricane later today. Minimum central pressure is 990 millibars (29.23")

Tropical Storm Katrina Intermediate Advisory Number 8B


Katrina continues to have an atypical concentration of strong winds. Rather than existing in the northeast quadrant just outside of the eye, they have been further from the center to the east and southeast of it. But as I mentioned in a previous update, for the first landfall, the worry is rain, not winds.

Radar shows that the heaviest of the thunderstorms are in the southeast quadrant, while most of the northern half of the storm consists of less intense activity and dry air. As such, the areas most concerned for flooding are the rectangle formed by Fort Lauderale, Miami, Everglades City, and Naples, with the rest of the peninsula south of that box also being of concern. Totals in excess of a foot of rain are possible in the area defined by the box I've described, while other areas will probably have totals running in the high single digits. The situation is not quite as dire as that of Tropical Storm Allison of 1999, which caused extremely damaging flooding, but it is rather serious nonetheless.

Looking beyond the first landfall...

One of the more difficult things to do is to have faith in your forecast and be Gibraltar-like in your confidence and paying only minimal attention to a single run of the models that may shake that confidence.

I must admit to going wobbly due to the model runs last night. I adjusted my unofficial too far east, partially owing to giving due to a model that I had more or less been disregarding (the GFS).

With deep apologies for the flip-flop, I restore my unoffical watch area for the second landfall to extend from Mobile Alabama to St Marks Florida. My area of highest concern extends from Panama City Beach to Appalachicola. Concerns that I expressed earlier for a significant hurricane for the Florida panhandle remain, especially if the hurricane gets to the western part of my 'watch area'.

Yesterday featured one plane doing an upper-air mission to sample the enviroment around the storm. Today, in addition to the Gulfstream-IV jet, a WC-130 will be taking upper-air observations in the over-water areas along the path of Katrina. Like last night, the data will be fed into the computer model's forecasts which will be generated late tonight.

At 11 AM EDT, the center of Tropical Storm Katrina was at 26.2 North 79.3 West, 55 miles east of Fort Lauderdale Florida and moving to the west at 6 mph with a further decrease in forward speed expected. On this course, Katrina will cross the coast tonight or early Friday morning. Maximum sustained winds are 60 mph and minimum central pressure is 997 millibars (29.44") (now 990, see discussion)

Tropical Storm Katrina Advisory Number Eight

Katrina is looking stronger on satellite and radar. Doppler radar has recorded some hurricane force winds at 10.000 feeton occasion, but the averages over a one mile square have been equivalent to 55 mph at the surface. The intensity estimate was a blend of the afforementioned doppler radar observations and estimates from satellite imagery. A recon plane with Stepped Frequency Microwave Radiometer capability is now in the storm and a recent report shows that pressure has dropped to 990 millibars, yet that pressure drop has yet to equate to an increase in wind speeds.

Upper-air data indicates that the upper-level ridge to the north of Katrina is shifting to the east, creating a steering current that would guide Katrina west. Models are in good agreement through 48 hours, but are split thereafter, with the UKMET being the furthest east (bringing the storm across northeast Florida with only a brief amount of time over the Gulf of Mexico) and the GFDL being furthest west (it takes the storm to Fort Walton Beach or so with a significant amount of time over water). The official forecast is an average of the NHC model guidance. Forecaster notes that the GFDL has been consistent in showing a southwest course across the peninsula of Florida, but he thinks that while the track is possible, it is an exxageration.

Dry air continues to affect Katrina, thereby keeping her intensity in check. Radar indicates that thunderstorms are now popping up in areas that were formerly dry. Given her slow forward speed and the fact that she is yet to cross the Gulf Stream, Katrina can still become a category one hurricane before landfall. Restrenghtening is expected after Katrina crosses into the Gulf of Mexico (second landfall is also forecast to be as a category one hurricane).

Tropical Storm Katrina Discussion Number Eight

Official forecast track

The eye of Katrina is now on Miami's short range radar.

The output of the global forecast models (with the upper-air data from NOAA's Gulfstream-IV jet) showed that my area of concern for the second landfall (Pensacola to St Mark's) is for the most part too far west. Accordingly, I'll adjust it to run from Panama City Beach to Yankeetown. The closer in to the coast of the peninsula that Katrina goes, the weaker she will be due to the shallow waters. A track along the GFDL forecast would put her over deeper water (with favorable warm temperatures extending most of the way down), thereby enabling the storm to become significantly stronger. Regardless of the exact track, it is clear that it will be a rainy few days for almost all of the Sunshine state.

For south Florida, the most significant problem will be the rain. Rain totals could run as high as a foot or greater in some areas due to how slow Katrina will be moving as she crosses the peninsula.

At 1 PM EDT the center of Tropical Storm Katrina was at 26.2 North 79.5 west, 40 miles east-northeast of Fort Lauderdale and 40 miles east-southeast of Boca Raton and moving to the west at 6 mph. Reports from the recon plane indicate that maximum sustained winds are up to 65 mph and pressure is down to 990 millibars (29.23"). Katrina could become a hurricane later today.

Tropical Storm Katrina Intermediate Advisory Number 8A

Nil else.