Torrential rains from 93L batter Puerto Rico

Tropical disturbance 93L is lashing Puerto Rico with torrential rains of up to four inches per hour. Flash floods and mudslides have been reported across the east, southeast, and southeastern interior Puerto Rico. Radar estimated rainfall (Figure 1) shows more than eight inches of rain has fallen in some regions. The winds are beginning to pick up on the island, with a personal weather station in Carolina, just southeast of San Juan, reporting sustained winds of 30 mph, gusting to 34 mph at 6:58 pm AST.

Infrared satellite loops show that heavy thunderstorm activity continues to increase in intensity, and upper-level outflow is now established on the north and east sides of 93L. Puerto Rico radar shows a large area of heavy rain advancing on the island, but there is no evidence of rotation or spiral bands beginning to form yet. Wind shear has fallen to the low level, about 5-10 knots.


Figure 1. Radar-estimated rainfall from 93L.

Expect heavy rains of up to 15 inches to affect Puerto Rico and the Virgin Islands through Monday from this slow moving storm. Heavy rains will also spread over eastern portions of the Dominican Republic Monday, potentially causing life-threatening flash floods and mudslides in mountainous regions. Since most of 93L's heavy thunderstorm activity is on its east side, it currently appears that Haiti and the Bahamas will escape dangerous heavy rains from this storm.

The intensity forecast
Wind shear is forecast to remain 10-20 knots over the next five days, and most of the reliable forecast models predict that 93L will develop into a tropical storm by Tuesday. The GFDL and HWRF models predict 93L will strengthen into a Category 1 or 2 hurricane by Friday. However, there will be high wind shear very close to 93L for the next five days, and the storm may struggle at times with this high shear. Water temperatures are a warm 29.5°C and ocean heat content will be moderate to high over the next five days. The NHC is giving 93L a high (>50% chance) of developing into a tropical depression by Tuesday. A Hurricane Hunter aircraft will investigate 93L Monday afternoon.

The track forecast
The models agree on a slow north-northwesterly motion for 93L over the next 3-4 days, which would bring the storm to a point between Bermuda and South Carolina. A major complicating factor in the long-range track forecast is the expected development of an extratropical Nor'easter storm off the coast of South Carolina on Wednesday or Thursday. The Nor'easter could bring hostile wind shear over 93L, weakening it, and potentially converting it into a subtropical storm. The two storms may rotate cyclonically around a common center (the Fujiwhara effect), sending the Nor'easter west-southwestward into the Southeast U.S., and 93L northwestwards towards North Carolina. This is the solution of the 18Z (2 pm EDT) GFDL and HWRF model. The NOGAPS model predicts that the Nor'easter will not develop at all, and instead 93L will absorb the energy that would have gone into creating the Nor'easter. This might convert 93L into a hybrid subtropical storm that would affect the coast of North and South Carolina late this week with sustained winds in the 50-60 mph range. I don't have a good feel for what will happen in this complicated situation, but it currently appears that coastal North Carolina may get tropical storm force winds from the extratropical storm beginning as early as Wednesday night. It is possible that 93L may impact the mid-Atlantic or New England regions early next week as a strong tropical storm.

Links to follow
Puerto Rico radar
San Juan, Puerto Rico weather

Portugul's storm
An extratropical low pressure system off the coast of Portugal has gradually warmed its core over the past 2-3 days, as it has wandered over waters of 22-23°C. This storm has developed some heavy thunderstorm activity near the center, and has winds of 40 mph, according to this evening's QuikSCAT pass. However, in NHC's subjective judgment, it does not yet have enough tropical characteristics to be named subtropical storm Kyle. This system should make landfall in southern Portugal Monday afternoon, bringing heavy rain and tropical storm force winds of 40 mph to the coast.

Hurricane Ike relief efforts
A group of wunderground bloggers have done some amazing work to gather, purchase, and deliver relief supplies to victims of Hurricane Ike. So far, the group (spearheaded by Presslord, StormJunkie, and Patrap) have raised over $12,000 and sent three truckloads of supplies, with another truck on the way, plus several air freight shipments. For photos of the effort, plus links to donate to the cause, visit stormjunkie's blog.

Jeff Masters