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TD 16 near tropical storm strength

By: Dr. Jeff Masters, 4:39 PM GMT on October 28, 2007

Tropical Depression 16 continues to get more organized today as it chugs slowly west-northwest at 6 mph. Long range radar out of Puerto Rico shows heavy rains affecting Puerto Rico and the Dominican Republic, and these rains are expected to spread over Haiti today. Satellite loops show very vigorous thunderstorms reaching high into the atmosphere have developed on the storm's northeast side. A recent microwave satellite image (Figure 1) shows rain rates of up to 1 inch per hour in these thunderstorms. Wind shear has fallen to 15-20 knots this morning, and is expected to fall below 15 knots later today. This should allow TD 16 to continue to develop, and it is probably already Tropical Storm Noel. The Hurricane Hunters are in the storm now, and will let us know more later this afternoon. The first flight of the NOAA jet is Monday night.

Figure 1. Microwave satellite image of TD 16 taken at 6:12 am EDT Sunday , 10/28/07. Rainfall rates over 1" per hour (orange colors) were observed to the northeast of the center of TD 16's circulation. Image credit: Navy Research Lab, Monterey.

This is a slow moving system that will dump very dangerous amounts of rain along its path. Of particular concern is the 8 to 12 inches of rain, with possible accumulations of up to 20 inches, forecast to fall over Haiti. Rains of this magnitude have killed thousands of people on Haiti in the recent past. Most recently, Hurricane Jeanne passed just north of Haiti as a tropical depression in 2004, and dumped about 13 inches of rain over the northern mountains. The resulting floods killed over 3,000 people. Heavy rains of up to 18 inches associated with a tropical disturbance in May 2004 also killed thousands.

The latest 00Z and 06Z models runs are similar to previous runs, and do not give us a lot of confidence that we know where TD 16 will go or how strong it will get. The key feature controlling TD 16's path is a trough of low pressure forecast to move off the U.S. East Coast four days from now. If this trough is strong enough, and TD 16 is large enough and far enough north, the trough will force TD 16 across Cuba, into the Bahamas, then northeastward out to sea. Exactly where this recurvature will occur is problematic, with the GFDL and HWRF predicting this will occur over the western Bahamas, and the GFS predicting a path close to Miami in the Eastern Bahamas. In either scenario, it is unlikely that TD 16 would affect South Florida as anything stronger than a Category 1 hurricane, since the storm must get through Cuba first, and deal with higher wind shear to the north of Cuba. If the storm makes a direct hit on South Florida this week, it would likely be as a tropical storm.

Another possibility, preferred by the NOGAPS and ECMWF models, is that TD 16 will stay south of Cuba and make it all the way to the extreme Western Caribbean near Mexico's Yucatan. The trough of low pressure forecast to move off the U.S. East Coast four days from now might not be strong enough to turn TD 16 northeastward in this case, and the storm could stay trapped in the Western Caribbean for many days. This scenario might allow TD 16 to intensify into a hurricane, and possibly a major hurricane, since wind shear is predicted to be light over the area, and the ocean heat content is high. This is the scenario I have been favoring, but this is a low-confidence forecast.

I'll have an update Monday morning, and perhaps late tonight.

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.