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Rains abate in Haiti as Tomas weakens

By: Dr. Jeff Masters, 8:24 PM GMT on November 05, 2010

Data from this afternoon's flight by the Hurricane Hunters shows that Tomas may have weakened to a tropical storm, though NHC is maintaining it as a hurricane in their 5pm advisory. The 3:28pm center fix found that Tomas' pressure had risen to 992 mb, and the top surface winds seen by the SFMR instrument were 64 mph. Highest winds at 10,000 feet were 74 mph, supporting reducing Tomas' status from hurricane to tropical storm--though it is possible that the aircraft did not sample the strongest winds of Tomas. The Gran Piedra, Cuba radar shows fewer echoes than this morning, and satellite loops also reveal a weakened storm, with much less heavy thunderstorm activity near the center. The weakening was probably due to the fact the center of Tomas passed very close to the rugged terrain of Haiti's southwest peninsula, and the rough mountains disrupted the flow into the developing eyewall of the hurricane. Conditions remain favorable for intensification, though, with wind shear a moderate 10 - 20 knots, and SSTs a very warm 29.5°C.

Figure 1. Visible MODIS satellite image taken by NASA's Terra satellite at 11:30am EDT November 5, 2010. image credit: NASA.

Impact on Hispaniola and Cuba
A trough of low pressure over the Eastern U.S. is drawing Tomas northeastward at 12 mph, and this forward speed will gradually increase to 15 mph by early Saturday morning. Tropical storm force winds of 39+ mph extend out about 140 miles to the east, and Tomas is probably bringing tropical storm force winds to the tip of eastern Cuba and Haiti's northwest peninsula at present. Rainfall is the primary concern from Tomas, though, not wind. Satellite estimates (Figure 2) indicate that Tomas dumped up to 4 - 6 inches of rain as of 8am EDT on much of southen Haiti; an additional 1 - 3 inches has probably fallen since then. However, the band of heavy rain to the south of Haiti that appeared poised to give southern Haiti an additional 3 - 6 inches of rain today got disrupted when Tomas' center brushed the mountainous tip of southwest Haiti. Thus, it appears the worst of the rain is over for Haiti. An additional 1 - 2 inches is possible in isolated regions, judging from recent satellite data. Preliminary news reports I've heard from Port-au-Prince indicate that the earthquake zone weathered the storm with no major loss of life. Severe flooding was reported on Haiti's southwest peninsula, with AP video showing 4 feet of water flowing through the streets of Leogane, 20 miles west of Port-au-Prince. It remains to be seen how the rest of Haiti fared, as satellite estimates of rainfall are often low, and do not properly measure the heavier rains that can fall in mountainous regions. A band of heavy rain is over the Dominican Republic this afternoon, and total rainfall amounts approaching ten inches in the mountains regions will likely cause dangerous flooding and mudslides in that country this afternoon and this evening.

Figure 2. Satellite-estimated rain amounts for the 24-hour period ending at 8am EDT Friday, November 5, 2010. Rainfall amounts of 4 - 6 inches (green colors) occurred over Costa Rica, the southwestern peninsula of Haiti, and isolated regions of the Dominican Republic and the rest of Haiti. Image credit: Navy Research Lab, Monterey.

Impact on the Southeast Bahamas and Turks and Caicos Islands
Although Tomas has been weakened by its close encounter with Haiti and now Cuba, the storm is in a favorable environment for re-intensification. I expect Tomas will re-intensify back to 85 mph winds by 2am EDT Saturday, as it passes through the Southeast Bahamas and Turks and Caicos Islands. Once Tomas pushes north of the islands on Sunday, the storm should weaken quickly, as wind shear is expected to rise to a very high 50 knots.

Tomas the second most damaging hurricane in St. Lucia history
Prime Minister Stephenson King announced yesterday that damage on the island of St.Lucia was $185 million--five times higher than earlier estimates. This sum is 19% of St. Lucia's GDP, and is the second most expensive hurricane ever for the island. Tomas damaged 10,000 homes and killed 14 people during its rampage over the island last Saturday. St. Lucia received the full brunt of the northern eyewall of Tomas as it intensified, and the St. Lucia weather service reported that sustained winds of 90 - 95 mph affected the island. Power has been restored to 90% of the island and most of the tourist facilities have reopened, however.

Tomas is the strongest hurricane to affect St. Lucia since Category 1 Hurricane Dean of 2007 brought 90 mph winds to the island. Dean killed one person and did $6.4 million in damage--0.5% of the nation's GDP. The island's strongest hurricane since accurate records began in 1851 was Hurricane Allen of 1980, which struck as a Category 3 hurricane with 130 mph winds. Allen killed 18 people on St.Lucia, and caused catastrophic damage of $235 million dollars ($613 million 2010 dollars.) This was 177% of the nation's GDP that year. The deadliest hurricane in St. Lucia history was the Category 5 Great Hurricane of 1780, which killed approximately 700 people. The Great Hurricane of 1780 was the Atlantic's deadliest hurricane of all-time, with 22,000 fatalities, mostly in the Lesser Antilles Islands.

Figure 3. Damage on St. Lucia from Hurricane Tomas. Image credit: St. Lucia Star.

Organizations Active in Haitian Relief Efforts:
Portlight disaster relief has shipped their mobile kitchen to Quisqueya, Haiti, and the kitchen will be ready to feed 500 people per day.
Lambi Fund of Haiti
Haiti Hope Fund
Catholic Relief Services of Haiti

Next update
I'll have an update Saturday morning.

My post on Haiti's hurricane history is now a permanent link in the "Articles of interest" section on our Tropical & Hurricane web page.

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.