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Puerto Rico and Hispaniola will get heavy rains from 98L

By: Dr. Jeff Masters, 4:53 PM GMT on October 12, 2008

A large region of low pressure (98L) has developed over the eastern Caribbean, a few hundred miles south of Puerto Rico. Wind shear is a high 20-25 knots over the disturbance, but waters are warm, about 29° C. This morning's QuikSCAT pass showed no closed surface circulation. Top winds seen by QuikSCAT were about 30 mph. The amount of heavy thunderstorm activity is moderate and increasing. At 3 pm EDT, visible satellite loops showed signs that a low level surface circulation may be starting to form near 15N 67.5W, about 200 miles south of the Mona Passage between Puerto Rico and the Dominican Republic.

Figure 1. Current satellite image of 98L.

The forecast for 98L
Wind shear is expected to fall to the moderate 15-20 knot range the next three days, and waters will remain warm, 29°C. This should allow 98L to slowly organize and approach tropical depression status 1-2 days from now. The UKMET, NOGAPS, and ECMWF models all indicate the 98L will come close to developing into a tropical depression by Wednesday, when it is expected to be near or over Hispaniola or Puerto Rico. The HWRF forecasts that 98L will organize into a tropical storm that will hit Puerto Rico Tuesday morning. Puerto Rico, the Dominican Republic, and the Virgin Islands are likely to receive heavy rains of 4-8 inches, with isolated amounts of 12 inches, during the period Monday through Thursday.

An upper-level low pressure system is expected to separate from the jet stream and park itself to the north of Puerto Rico by Tuesday. The counter-clockwise flow of air around this low should draw 98L to the north across Puerto Rico and Hispaniola by Wednesday. NHC is giving 97L a medium (20-50% chance) of developing into a tropical depression by Tuesday.

An area of disturbed weather (97L) midway between Africa and the Lesser Antilles Islands has developed a well-organized closed circulation. However, wind shear of 30 knots is allowing just a small amount of heavy thunderstorm activity to cling to the east side of the storm. This morning's QuikSCAT pass saw winds of 40-45 mph in these heavy thunderstorms. Satellite loops show the classic signature of a tropical cyclone under high wind shear--a low level circulation center exposed to view, with a clump of heavy thunderstorms on the side away from where strong upper-level winds are blowing.

Figure 2. Current satellite image of 97L.

The forecast for 97L
There is a chance shear may relax a little this afternoon, which may allow enough heavy thunderstorm activity to build and convince NHC to call this system Tropical Storm Nana. Wind shear is expected to rise to the high 35-40 knot range Monday and Tuesday, which should prevent any further development. NHC is giving 97L a high (>50% chance) of developing into a tropical depression by Tuesday.

Elsewhere in the Atlantic
Most of the models continue to forecast the possible development of a tropical depression in the south central Caribbean, off the coast of Nicaragua, 5-7 days from now.

Figure 3. Hurricane Norbert over the Gulf of California at 23:45 GMT Saturday October 11, 2008. At the time, Norbert was a Category 1 hurricane with 85 mph winds. Tropical Storm Odile is visible at lower right. Image credit: NASA Goddard.

Hurricane Norbert made landfall on the west coast of Mexico's Baja Peninsula Saturday afternoon as a Category 2 hurricane with 105 mph winds. Norbert crossed Baja and the Gulf of California, making a second landfall on mainland Mexico as a Category 1 hurricane with 85 mph winds. Norbert made landfall along a sparsely populated stretch of the coast about 145 miles northwest of the resort town of Cabo San Lucas. The storm tore off roofs and flooded homes knee-deep in the town of Puerto San Carlos, near where the eye came ashore. The remains of Norbert are expected to slosh into the Midwestern U.S. on Monday and combine with an area of low pressure over Kansas. The resulting storm could trigger rains in excess of seven inches, according to the latest forecast from NOAA's Hydrometeorological Prediction Center (Figure 4).

Figure 4. Forecast rain amounts for the five-day period ending Friday, October 17, 2008. Image credit: NOAA/HPC.

Saturday's update on Hurricane Ike relief efforts
I got this very nice email yesterday, giving appreciation for all those who helped out through the portlight.org Hurricane Ike charity effort:

I just wanted to express my sincere gratitude, on behalf of the City of Houston, the Mayor, and our community partners over at TIRR/Memorial Hermann, for all of your involvement in bringing medical supplies and equipment together to help Texans with disabilities affected by Hurricane Ike. I can't tell you how much we all appreciate the fact that you so quickly mobilized and leveraged such a tremendous amount of support to bring these needed items to Houston and other Texas cities.

An email simply doesn't do justice to the generous spirit and initiative that you, Paul Timmons, and your partners took to make this happen, nor to our gratitude. However, I just want you to know that we think about you all in appreciation every single day over here, and there are many who are directly benefiting from your generosity.

By the way, Paul Timmons mentioned that it looks like another shipment of 30-50 wheelchairs can be sent over here. All I can say is wow! Thank you for not forgetting about us, and for realizing that we still have a lot of needs here that we are trying to meet - even 4 weeks after the hurricane.

Again, please accept my sincere thanks. I hope that you have a wonderful weekend!

Michelle Colvard, MPH
Executive Director
Mayor's Office for People with Disabilities

Contributions to this highly worthy portlight.org charity fund are fully tax-deductible, and will go to provide relief supplies for those smaller communities typically bypassed by the traditional relief efforts. More details can be found at StormJunkie's blog.

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.