Wilma: nightmare for Mexico

Hurricane Wilma made its expected turn northwest, and is now headed towards Cozumel Island as an extremely dangerous Category 4 hurricane capable of massive destruction. A new hurricane hunter plane arrived at the center at 2:45 pm EDT, and found a central pressure of 918 mb and surface winds of 150 mph. The 4:16 pm report had the same pressure and winds, so Wilma has leveled out in intensity. Wilma has completed an eyewall replacement cycle, and now has a large 40 mile diameter eye. Some intensification is likely the next 18 hours before Wilma comes ashore in the Yucatan. It is possible Wilma can eclipse its record 882 mb pressure, but she probably will not have enough time to do that.


FIgure 1. Topography of the ocean bottom. Where a long expanse of shallow waters over the Continental Shelf (light blue) exist next to the coast, one can expect increased storm surge potential. The waters off the coast of Cancun/Cozumel are quite deep, limiting the maximum potential storm surge to about 11 feet. The Continental Shelf is quite extensive off the west coast of Florida, making that region prone to large storm surges. Image credit: NOAA.

Wilma's impact on Mexico
Wilma's impact on Mexico is likely to be catastrophic. A 50-mile wide stretch of coast will receive Category 4 to 5 sustained winds of over 150 mph, causing incredible damage. As Wilma sits in place for two days, the long duration of high winds will cause far more damage than a quickly moving storm would. The long duration extreme winds will probably cause some of the worst wind damage ever seen in a hurricane. The storm surge will not be as much as a problem, because deep water just offshore will prevent a huge storm surge from piling up. Still, the expected storm surge of up to 11 feet will cause widespread damage to coastal structures.In adddition, rainfall amounts of 15 - 25 will cause serious flooding. Wilma is likely to be Mexico's worst weather disaster in history.


Figure 2. Computer model tracks for Hurricane Wilma.

Where will Wilma go?
A trough of low pressure moving across the central U.S. has turned Wilma more to the northwest today, on a track towards Cozumel Island. The lastest 12Z (8am EDT) runs of all four major models used to track hurricanes--the GFS, GFDL, NOGAPS, and UKMET--agree on a landfall on Mexico's Yucatan Peninsula Friday, followed by a one to two day period of slow and erratic movement over land. By Sunday, strong westerly winds fill in behind the trough and pick up Wilma, and move her across South Florida by Monday. Once Wilma does make the crossing from Mexico to Florida, I expect little change in strength. While the waters are still warm enough to support intensification, this will be offset by increasing wind shear associated with the westerly winds driving Wilma.

How believable is all this? As we've seen many times this hurricane season, when the models come into alignment, it's usually a good sign that the forecast is correct. This is particularly true when data from the NOAA jet is used to initialize the models, which is the case here. However, in a case where the steering currents are weak, there is much less confidence. In addition, just a small 100 mile error in forecast means the difference between Wilma staying over warm waters and maintaining its intensity, or moving ashore and weakening significantly. The Canadian model (which has not performed well with Wilma) is forecasting that she will stay primarily over water the next three days.

Given all these factors, I'd give Wilma a 10% chance of arriving on the Florida west coast as a Category 3 or higher storm, 20% as a Category 2, 40% as a Category 1, and 30% as a tropical storm. On Florida's east coast, knock these value down by half a Category (10 - 15 mph).

After Florida, then what?
There is no change to the forecast. After crossing Florida, Wilma is threat to the northern Bahama Islands. Wilma should pass well offshore North Carolina, but close enough to bring tropical storm force winds to the Outer Banks. Wilma is expected to merge with a large low pressure system as she approaches Maine or Nova Scotia next week, and could bring tropical storm force winds to Cape Cod, Maine, and the Canadian Maritime provinces.

What's behind Wilma?
There is a large area of disorganized thunderstorms near 12N 57W, about 300 miles east of the Leeward Islands. Wind shear is too high to permit development of this area over the next day or two.

I'll be back tomorrow with the lastest. For those of you in Florida looking for storm surge maps of your county, check out the floridadisaster.org website.

Jeff Masters