Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 10:43 PM GMT on October 22, 2005
Ever since the formation of two major hurricanes in July made it clear that the Hurricane Season of 2005 was going to challenge 1933 as the busiest season ever, I've been expecting to see the words "Tropical Storm Alpha" emblazoned on a hurricane tracking chart. Well, we've got the record now. The formation of Tropical Storm Alpha, the 22nd storm of the season, now makes 2005 the busiest hurricane season of all time. Still, it looks really strange to see the words "Tropical Storm Alpha" on the hurricane tracking charts, and gives a surreal cast to Hurricane Season of 2005 as we approach the Halloween season.
In keeping with the season, we have two very scary storms to talk about. The eye of very dangerous Category 2 Hurricane Wilma is moving offshore the Yucatan mainland this evening, a little earlier than I expected. This makes it more likely Wilma will be a bit stronger at landfall in Florida Monday--perhaps a strong Category 2 with 105 mph winds. We are not good at making intensity forecasts, and Wilma could easily be a Category stronger--or weaker. The argument for a weaker hurricane goes like this: Wilma's inner eyewall has collapsed, leaving an outer eyewall with diameter 80 miles in place. When an inner eyewall collapses like that, it usually takes at least a day for the eyewall to reform, and by a day from now, Wilma will start experiencing increased wind shear which will weaken her down to a Category 1.
The argument for a stronger hurricane goes like this: Wilma still has a large, intact circulation, and is still a Category 2 hurricane. She will not follow the usual normals (since this is the Hurricane Season of 2005, after all), and will re-intensify quickly over the warm waters that nurtured her rise to Category 5 status this week. By late Sunday, she will be a Category 3 hurricane again, and large enough and fast moving enough that the shear affecting her will be unable to significantly weaken her. Wilma will make landfall as a major hurricane on Florida's west coast.
So, both scenarios are plausible, and Florida must be prepared for the arrival of a major hurricane on Monday. Landfall anywhere between Sarasota and the Keys is possible.
The remainder of my 1 pm post appears below, mostly unchanged.
The most extreme winds of the eyewall have now been battering Cozumel and the mainland Yucatan Peninsula for over 30 hours. Sustained winds of 100 - 140 mph affecting a built-up resort area like Cozumel/Cancun for so long must have done extreme damage. Wilma has weakened to a Category 2 hurricane with 100 mph winds. Still, the damage to Mexico will increase today as structures already weakened by 30 hours of relentless winds continue to receive another 12 hours of stress.
Conditions in Cancun
Wunderblogger LizinCancun reported yesterday on conditions in Cancun:
"We evacuated our home in Cancun yesterday and came 200 miles west to Merida. Our home sits about 100 feet away from the beach. The waves were crashing over our 6 foot tall sea wall yesterday before we left and destroyed the palapa that sits about 10 feet out in the water. We fully expect our home and all our belongings to be gone. We lost contact with all of our friends that stayed, cell and land lines are down of course as is power. We just talked with a friend that says the power is out, phones only working when the generators are running to pump out all the water. He said the hotel is blowing apart (not in the hotel zone) and all you can see when looking outside is a wall of water blowing sideways and pieces of things being shredded by the high winds, some huge."
Figure 1. Total rainfall for the week. Image generated by NASA's TRMM rainfall measuring satellite.
A deluge of rain
Rainfall amounts in Mexico from Wilma have been extreme. Isla Mujeres, just offshore from Cancun, has reported almost 35" of rain over the past 1 1/2 days, and at one point reported 4" of rain in one hour between 2 and 3 am EDT today. Rainfall amounts in Cuba have not been nearly so extreme--at least in the areas of western Cuba that are still reporting data. San Juan y Martinez measured 10.7 cm (4.2 inches) of rain the past 24 hours, and storm total rainfall amounts of up to 18 cm (7 inches) have been measured in Cuba's westernmost province. Grand Cayman received five inches, Jamaica's Kingston airport eight inches, and Belize four inches. The north coast of Honduras has had numerous locations receive ten inches of rain, with one unofficial report of 20 inches. Rainfall in Haiti reached 8 - 10 inches, and, triggered flash floods that killed 11 people.
How will Wilma affect Florida?
The latest 8 am EDT (12Z) model runs are in, and continue to agree on the basic scenario that Wilma will move offshore the Yucatan tonight as a weak Category 2 hurricane. On Sunday, the storm will move slowly north and then northeast as westerly winds from a strong trough of low pressure start affecting the storm. There is about an 18-hour window of opportunity for Wilma to re-intensify to a Category 3 hurricane on Sunday. By Sunday night, the Wilma will begin to accelerate, and wind shear will begin to weaken the storm. By Monday morning, Wilma will cross the west coast of Florida between Fort Myers and the Keys as a Category 1, 2, or 3 hurricane. My best guess is that Wilma will be a 110-mph Category 2 hurricane hitting near Marco. Storm surges tend to be worse with large and faster moving hurricanes, so I would expect a storm surge characteristic of a Category 3 hurricane, 10 to 16 feet, in and south of Marco, causing very heavy damage in that city. Fortunately, the area south of Marco is primarily uninhabited--the Everglades swamp. However, if Wilma comes ashore north of Naples--or further south near the Keys--storm surge flood damage in those areas could easily reach billions of dollars. Storm surge flooding should be only 2 - 4 feet on the east coast of Florida, where wind damage is the primary threat.
Figure 2. Storm surge map for southwest Florida.
Wilma's winds and rain
Wilma will be moving too fast to dump more than 5 - 10 inches of rain. The rain will be concentrated on the north side of the hurricane, since there will be a cold front there that will trigger more condensation. Areas to the north of the eye's passage will see winds a full Category--25 to 30 mph--lower than those on the south. This is because the storm's high rate of forward motion, near 25 - 30 mph, will add to the windspeeds seen on the south side of the Wilma's counterclockwise rotation, and subtract on the north side. Since the storm will be moving so fast, the duration of hurricane force winds will be just a few hours.
After Florida, then what?
After crossing Florida, Wilma should bring tropical storm force winds to the northern Bahama Islands, but not hurricane force winds. Wilma should pass close enough to North Carolina's Outer Banks to bring 40 mph winds there. Wilma is not expected to bring high winds to New England, but could bring 50 mph winds to Nova Scotia five days from now.
Alpha has formed 200 miles southeast of Hispanolia. Long range radar from San Juan, Puerto Rico shows some increasing spiral banding and echo intensity, and satellite imagery shows a good outflow channel developing to the southeast. Wind shear of about 10 knots is eroding the northwest portion of the storm.
Given the storm's expected track over Haiti, the 8 - 12 inches of rain expected may cause heavy loss of life in that country due to the inability of the deforested hillsides to handle flood waters. The Dominican Republic, which still has 70% of its forest cover, should fare relatively well.
I'll be back in the morning with the latest.
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