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Hurricane Tomas lashing Haiti with torrential rains

By: Dr. Jeff Masters, 1:57 PM GMT on November 05, 2010

Deadly Hurricane Tomas has intensified into a dangerous Category 1 hurricane with 85 mph winds this morning, and is lashing Haiti, eastern Cuba, and the southwestern coast of the Dominican Republic with torrential rains. Observations from the Gran Piedra, Cuba radar show that the eye of Tomas is skirting the tip of the southwestern Peninsula of Haiti, and the winds of the powerful eastern eyewall of the storm are pounding the western end of the peninsula. An Air Force hurricane hunter aircraft just left Tomas, and measured top surface winds of 86 mph at 7:13am EDT. Satellite loops of Tomas show an impressive Central Dense Overcast (CDO) of high cirrus clouds with very cold tops has pushed into the lower stratosphere above Tomas and has flattened out, hiding the surface center from view. An eye is not yet visible on satellite imagery. The latest center fix at 7:08am EDT found that the pressure had risen slightly to 988 mb, which may be a sign that interaction with the mountainous terrain of southwestern Haiti may have caused some disruption of Tomas. However, Tomas should resume intensifying this afternoon now that the center has moved past the southwestern tip of Haiti, as wind shear is a moderate 10 - 20 knots, and SSTs are a very warm 29.5°C.

Figure 1. Rainfall rate for Tomas as observed by the F-17 polar orbiting satellite at 6:42am EDT Friday, November 5, 2010. Heaviest rainfall rates in excess of 1.4 inches per hour (pink colors) were in the west eyewall, and are likely to miss Haiti. However, a long band of intense rain (1/2" - 3/4" per hour) extended to the southwest of Port-au-Prince, and these rains will impact the cities in Haiti most vulnerable to catastrophic flooding, Port-au-Prince and Gonaives. Image credit: Navy Research Lab, Monterey.

Impact on Hispaniola and Cuba
A trough of low pressure over the Eastern U.S. is drawing Tomas northeastward at 9 mph, and this forward speed will gradually increase to 15 mph by early Saturday morning. Hurricane force winds extend outwards only 15 miles to the east of Tomas' center, and only the extreme tips of Haiti's southwest and northwest peninsulas will receive hurricane force winds. Tropical storm force winds of 39+ mph extend out about 140 miles to the east, and Tomas will pass far enough from the Port-au-Prince earthquake zone that winds there will not exceed 30 - 35 mph. However, the northern Haitian city of Gonaives will receive 40 - 45 mph winds this afternoon and this evening, as will the eastern tip of Cuba. Rainfall is the primary concern from Tomas, though, not wind. Satellite estimates (Figure 1) indicate that Tomas has already dumped up to 6 inches of rain on Haiti's southwest peninsula, and 3 inches in the Port-au-Prince earthquake zone. Recent microwave imagery (Figure 2) shows that while the heaviest rains from Tomas lie in the west eyewall and will miss Haiti, a long band of heavy rain with rainfall rates of 1/2" - 3/4" per hour lies to the southwest of Port-au-Prince and Gonaives, the two most vulnerable cities in Haiti to catastrophic flooding. The rain band is lined up to bring the earthquake zone of Haiti an additional 3" - 6" of rain today and tonight, bringing the storm total for Port-au-Prince and the surrounding mountains to 6" - 9". Rains of this magnitude are likely to cause extremely dangerous flooding for the 1.3 million Haitians living in makeshift refugee camps, and may cause heavy loss of life. Also of concern is the rains that will fall in northwestern Haiti, particularly in the highly vulnerable city of Gonaives, where rains from Tropical Storm Jeanne in 2004 killed 3,000 people. A band of heavy rain will also affect the southern Dominican Republic today, and total rainfall amounts approaching ten inches in the mountains near the southwestern coast will likely cause dangerous flooding and mudslides.

Figure 2. Satellite-estimated rain amounts for the 24-hour period ending at 2am EDT Friday, November 5, 2010. Rainfall amounts of up to 6 inches (dark green colors) occurred over Costa Rica and the extreme southwestern tip of Haiti. Image credit: Navy Research Lab, Monterey.

Impact on the Southeast Bahamas and Turks and Caicos Islands
Tomas appears likely to thread the narrow gap of water between Cuba and Haiti, and will likely emerge into the Southeast Bahamas and Turks and Caicos Islands as a Category 1 hurricane. According to the 5am EDT NHC wind radius forecast (Figure 3), tropical storm force winds of 39+ mph should begin in the Inagua Islands by noon today, then spread to the Turks and Caicos Islands by 3pm EDT. A 30-mile wide swath along the center of Tomas' path will receive hurricane force winds of 74+ mph. 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.

Figure 3. Predicted position and location of Tomas' tropical storm force winds (dark green colors) and hurricane force winds (yellow colors) as predicted in the 5am EDT NHC advisory.

Costa Rica mudslides kill 20
Mudslides killed at least 20 people in Costa Rica yesterday, after heavy rains sent mud rushing over at least five homes in San Antonio de Escazu, a suburb of the nation's capital. A very moist flow of Pacific air been drawn eastwards over Central America over the past three days by Hurricane Tomas, triggering the heavy rains in Costa Rica. This moisture has also been drawn into Hurricane Tomas, and is helping fuel the heavy rains over Haiti. Satellite observations (Figure 2) suggest that up to 6 inches of rain fell over Costa Rica during the 24 hours ending at 2am EDT this morning. Earlier in the week, an additional 2 - 6 inches of rain had fallen over the nation.

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 this afternoon.

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.