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New computer model runs for Katrina

By: Dr. Jeff Masters, 7:11 PM GMT on August 25, 2005

The 1:18pm EDT Hurricane Hunter mission found the pressure of Katrina remained constant at 990mb, but the maximum winds were now on the northwest side at 64 knots (73 mph) at the airplane's flight level of 5000 feet. Radar from Miami confirms that the north side of Katrina has greatly increased in the amount and intensity of precipitation the past two hours as the storm continues to strengthen. It is a very good thing that Katrina does not have an extra 12 hours to intensify before landfall! However, the very favorable environment for intensification that Katrina is currently in is expected to still exist once she is in the Gulf of Mexico Saturday. I expect Katrina will become at least a Category 2 hurricane before its second landfall.

The latest computer model runs, performed using the 8am EDT upper air data, have made a major shift. Katrina is expected to push much farther west off of the western coast of Florida, and make a delayed turn to the north. These latest model runs show a much reduced risk to Tampa, and put an area from New Orleans to Cedar Key, Florida at risk. In the center of this risk area lies the U.S.'s very own hurricane magnet, the Pensacola region, where Ivan and Dennis struck.

Katrina continues to intensify at a modest pace, and if present trends continue will hit Florida near Fort Lauderdale tonight as a minimal Category 1 hurricane with 75 - 80 mph winds. The northwest side of the storm continues to suffer from dry air intrusions, and the primary intense thunderstorms and strongest winds are on the south side. Thus, the usual rule about the right front quadrant (north side) of the storm being the most dangerous is not neccesarily the case with Katrina. The highest storm surge will still be to the north of where the center comes ashore, but wind damage may be equally distributed on both sides of the storm.

The Miami radar loop continues to show an increase in low-level banding, and an eye-like feature trying to form. Upper level outflow is improving and slowing expanding.

As I discussed in the previous blog entry, the major threat to South Florida from Katrina is freshwater flooding from her rains. Rainfall amounts of 6 - 10 inches are expected from this slow-moving storm. For comparison, Hurricane Irene of 1999, which hit South Florida as a Category 1 hurricane, dumped 10 - 20 inches of rain. Damage from Irene was over $800 million in Florida. Damage from Katrina will probably be much lower, in the $30 - $100 million range, since Katrina's rainfall will be half of what Irene's was.

What's that behind Katrina?
A large area of disturbed weather even bigger than Katrina lies to her east, just north of Hispanolia. This disturbance lies in an area of high wind shear of 25 - 35 knots, and is not a threat to develop into a tropical depression in the next few days.

Katrina blogs
For observations of what's happening now in South Florida, we have several bloggers writing today:

turtlehurricane (Weston, Broward County)

sngalla (Fort Lauderdale)

MrJ76 (Okeechobee)

Zeenster (Cape Coral, SW Florida)

evolution (Charlotte Harbor, SW Florida)

Dr. Jeff Masters

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.