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.


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