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Noel dumping torrential rains on the Dominican Republic

By: Dr. Jeff Masters, 2:28 PM GMT on October 29, 2007

Tropical Storm Noel hit Haiti this morning just south of the capital of Port-Au-Prince, dumping prodigious rains of over one inch per hour over some regions of the island of Hispaniola. The storm's slow forward speed means that heavy rains will affect the island for several more days. Long range radar out of Puerto Rico shows heavy rains affecting the Dominican Republic. These rains have already exceeded eight inches over a wide area of ocean to the east of Noel's center, according to rainfall estimates from the Puerto Rico radar. Rainfall amounts of 4-7 inches over southern Puerto Rico have triggered numerous flash floods and landslides.

This morning's QuikSCAT pass showed top winds of about 50 mph over a small region north of Hispaniola. Wind and storm surge damage should be minimal on Hispaniola from Noel.

The Dominican Republic
The worst of the rains for Puerto Rico are now over, but the flooding situation on Hispaniola today will be extremely serious, particularly in the Dominican Republic. Satellite loops show very vigorous thunderstorms reaching high into the atmosphere roiling over Hispaniola. Early this morning, these thunderstorms dumped about 150 mm (6 inches) of rain in just six hours in a region southwest of the capital of the Dominican Republic, Santo Domingo (Figure 1). Santo Domingo reported a visibility of zero at 2am local time during this heavy rain. Rainfall amount of about 12 inches have fallen over the Dominican Republic's southernmost point, the Barahona Peninsula, according to satellite estimates. The region's only airport weather station stopped transmitting data at 8pm last night.

So far, Haiti has escaped the worst of Noel's heavy rains, giving hope that a repeat of the floods triggered by Hurricane Jeanne in 2004 might be avoided. Jeanne passed just north of Haiti as a tropical storm, and dumped about 13 inches of rain over the northern mountains. The resulting floods killed over 3,000 people. However, satellite images show that a large region of disturbed weather to the southeast of Hispaniola associated with Noel, and Noel's counter-clockwise circulation will pull heavy rains over Hispaniola for the next two days. I still expect that some regions of Haiti will receive over 12 inches of rain from Noel.

Figure 1. Satellite estimates of rain for the 6-hour period ending at 5 am EDT Monday, 10/29/07. Note the red "bulls-eye" at upper right of the image over Hispaniola, indicating heavy rain of about 150 mm (6 inches) fell in just six hours. Image credit: Navy Research Lab, Monterey.

The track forecast
Passage over the rugged terrain of Haiti has severely disrupted Noel, and satellite imagery suggests that the center of the storm is now trying to reform just north of Hispaniola. The latest computer model runs from 00Z and 06Z this morning continue to show a wide range of solutions for Noel's path. All of the models forecast that Noel's current north-northwest motion will continue today, in response to the counter-clockwise flow of air around an upper level low to the west of Noel. This upper low is forecast to weaken over the next few days, allowing a ridge of high pressure to build in, which will force Noel to the northwest or west-northwest. The GFS, NOGAPS, GFDL, and HWRF models all take Noel through the Bahamas, to the north of Cuba. The UKMET and ECMWF take Noel to the south of Cuba, close to its coast. This is unlikely, since Noel's center is trying to reform to the north of Hispaniola. The key question is the timing and strength of a trough of low pressure forecast to move off the U.S. East Coast Thursday. A slower arrival of this trough will allow Noel to penetrate farther west into the western Bahamas. The NOGAPS and GFS models foresee that Noel will reach a point between 100-300 miles east of South Florida before recurving out to sea. The HWRF and GFDL recurve Noel much further to the east. The GFDL doesn't take Noel very far west at all, predicting that the storm will graze the eastern Bahamas, then accelerate to the northeast and threaten Bermuda as a strong tropical storm on Friday. Given that Noel appears to be taking a big jump to the north and reforming north of Haiti this morning, I would expect that the official NHC forecast is the correct one, and Noel will recurve before reaching the western Bahamas.

The intensity forecast
Noel's intensity will be controlled by its interaction with the land masses of Hispaniola and Cuba over the next day. Passage over the mountainous terrain of Haiti has severely disrupted Noel, and any intensification over the next day should be slow. Wind shear is about 10-20 knots today, and is expected to remain in that range over the next two days. This will allow some slow strengthening of Noel if its center can remain over water. I give Noel a 40% chance of reaching hurricane strength at some point. After two days, wind shear is expected to increase above 20 knots, and Noel should weaken.

I'll have an update late this afternoon.

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.