Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather
By: Dr. Jeff Masters , 1:52 PM GMT on October 20, 2005
Hurricane Wilma continues across the western Caribbean towards Mexico as a extremely dangerous Category 4 hurricane capable of massive destruction. Wilma is currently undergoing a collapse of her inner eyewall, which will cause a short weakening trend that may last the remainder of the day. The inner eyewall of eight miles diameter is collapsing, and a new eyewall of 40 miles diameter is forming. This will reduce Wilma's peak winds to perhaps 135 mph today, at the low end of Category 4 strength. We'll have to wait until the next hurricane hunter mission arrives around 4 pm today to verify if this is the case.
As Wilma's eye reforms at a much larger size, the hurricane should begin to intensify again, and a return to Category 5 strength by Friday afternoon is a possibility. The larger eye will result in a much larger area being exposed to the extreme winds of the eyewall. If Wilma makes landfall along the Yucatan Peninsula, a stretch of coast perhaps 50 miles long will experience extreme damage.
Figure 1. Computer model tracks for Hurricane Wilma.
Where will Wilma go?
There is still a high degree of uncertainty in the forecast for Wilma. NHC has not adjusted the official forecast much the past few days, which is wise when the computer models are having difficulty. A trough of low pressure moving across the central U.S. should turn Wilma northwest today towards Cozumel Island, and then due north by tomorrow. However, once Wilma reaches the vicinity of Cancun and Cozumel, the storm is expected to slow to a crawl or stall for 12 - 48 hours. This will result in the northeast tip of the Yucatan Peninsula receiving a horrific pounding, particularly if the eye comes ashore. This weekend is a very bad weekend to be a tourist in Cancun.
Finally, by Saturday, strong westerly winds will build in behind the trough and carry Wilma rapidly northeastward across South Florida or the waters between Florida and Cuba.
The absolutely critical thing is--where will Wilma stall out? The GFDL model believes Wilma will push inland over the tip of the Yucatan, and spend two days overland, and weaken to a tropical storm. The UKMET model believes Wilma will stall in the Yucatan Channel, and not lose much strength. The other models have modest variations on these two themes. The difference in postions is only 100 miles or so. This is impossible to reliably forecast even 12 hours in advance, given the weak steering currents that are likely to exist Friday. Will will just have to wait and see what happens. Very small changes in storm position will cause huge changes in Wilma's intensity.
A long encounter with the Yucatan Peninsula would cause a serious disruption of the hurricane. While the waters are still warm enough to support intensification once she starts moving through the Gulf of Mexico towards Florida, there will be increasing wind shear associated with the westerly winds driving Wilma that will inhibit intensification. In addition, Wilma will only have a day or so to intensify, as the westerly winds will accelerate her to a forward speed of about 30 mph once she approaches Florida. Wilma's likely intensity once she reaches Florida is tropical storm to Category 3 strength.
Figure 2. Storm surge map for the southwest coast of Florida.
What kind of storm surge might affect Florida?
One can see from the storm surge map above that the southwest coast of Florida is very prone to high storm surges. This is because the Continental Shelf extends about 100 miles offshore, creating a very shallow area for the storm surge waters to build up in. If Wilma does hit the southwest coast of Florida as a Category 3 hurricane, which is the upper end of the intensity I think is likely, a 10 - 16 foot storm surge could flood most of Naples and all of Marco. Given the expected high forward speed of the hurricane at landfall in Florida--25 to 30 mph--regions to the south side of where the eye makes landfall will receive far greater wind damage and storm surge than is typical for a hurricane.
After Florida, then what?
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 of Nova Scotia about five days from now, and could bring tropical storm force winds to New England and the Canadian Maritime provinces.
I'll be back this afternoon about 4 pm EDT with an update on the latest, and post a storm surge map for the Keys if I can locate one.
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