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Disturbance 90L continues towards the Western Caribbean

By: Dr. Jeff Masters, 12:31 PM GMT on October 27, 2007

A surface low pressure system (90L) moved over Puerto Rico Friday, and is now centered about 175 miles south of Santo Domingo in the Dominican Republic. The system has maintained its spin and some respectable heavy thunderstorm activity in the face of some hostile wind shear of 30-35 over the past day. This wind shear has fallen to 20-30 knots this morning, which is still too high to allow development today. Long range radar of of Puerto Rico shows isolated bands of heavy rain that are not well-organized continue to affect the region. Satellite loops show most of the heavy thunderstorm activity is to the east of the low's center of circulation, and the high wind shear is keeping this thunderstorm activity disorganized. This morning's QuikSCAT pass showed a well-formed circulation with top winds of about 30 mph to the north of the center.

Figure 1. Lastest satellite rainfall estimate of 90L.

The system is headed west at about 10 mph, and will continue to bring heavy rains and the threat of flash flooding and mudslides to Puerto Rico today. Heavy rains of up to 4 inches have already fallen in southest Puerto Rico and the Virgin Islands so far from this storm. (Figure 1). Heavy rains may also affect the Dominican Republic and Haiti today and Sunday.

The computer models forecasts this morning are similar to yesterday's runs, although some of the guidance has shifted further northwards, implying more of threat to Cuba, the Bahamas, and South Florida. It is possible 90L could intensify into a tropical depression as early as Sunday, since wind shear will fall below 20 knots by then. The Hurricane Hunters are on call to fly Sunday afternoon, if necessary. The UKMET, ECMWF, and NOGAPS models predict that 90L will develop into a tropical storm by Monday as it moves slowly into the Western Caribbean, just south of Cuba. This track would favor 90L developing into a hurricane late next week. NOGAPS indicates 90L might turn northwards over South Florida late next week, but the other two models keep 90L trapped in the Western Caribbean. The GFS model keeps wind shear 15-25 knots through the period, and does not develop 90L. The HWRF and GFDL models suggest 90L may move down the length of Cuba then into the Bahamas and recurve to the northeast, missing South Florida. This sort of significant interaction with land would keep 90L from developing into a hurricane, and these models predict just a weak tropical storm will form.

One possible wild card is the disturbed area of weather that has formed in the extreme Western Caribbean, just east of the Yucatan Peninsula. This disturbance is currently very disorganized, but is under only 10 knots of wind shear. If it starts to develop early next week, it could alter the path and development of 90L.

Residents and visitors to the Western Caribbean should continue to anticipate the possibility of a hurricane forming in the Western Caribbean by late next week.

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.