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).