Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 9:53 PM GMT on September 22, 2008
Tropical disturbance 93L continues to dump torrential rains on Puerto Rico, the Virgin Islands, and the eastern Dominican Republic. The storm is being blamed for four deaths in Puerto Rico--two from drowning, and two from heart attacks. The southeastern county of Patillas recorded 24 inches of rain in 24 hours. The Rio Gurabo River rose 25 feet in just 12 hours today, peaking at just over 30 feet high--12 feet over flood stage. This broke the record flood set in 1998 during Hurricane Georges at this station (Figure 1).
Figure 1. Height of the Rio Gurabo River in southeast Puerto Rico during the passage of 93L on September 22, 2008. The river rose from a height of five feet to 30 feet in just 12 hours. Image credit: U.S. Geological Survey. To see an interactive map of stream flow data, use the wundermap for Puerto Rico, and turn on the "USGS River Height" layer.
Data from the Hurricane Hunters, Dominican Republic radar, and visible satellite loops indicate that the center of 93L has tracked west-northwest along the north coast of the Dominican Republic today, just inland. The storm does appear to have a closed low-level circulation, and a limited (but increasing) amount of heavy thunderstorm activity near the center. Wind shear of 15-20 knots due to strong upper-level westerly winds is keeping most of 93L's heavy thunderstorm activity well south and east of the storm. These thunderstorms will continue to bring up to eight inches of rain to Puerto Rico and the Virgin Islands through Tuesday night. The Hurricane Hunters found a large area of winds in the 30-35 mph range, and one could argue that this is already a tropical depression. However, unless the center pops off the coast in the next 12 hours, the storm could get significantly disrupted by Hispaniola, and NHC is waiting to see how this land interaction goes before naming it a tropical depression.
Here's NHC's latest take on 93L:
special tropical disturbance statement
445 PM EDT Mon Sep 22 2008
Reports from an Air Force Reserve hurricane hunter aircraft and surface observations indicate that the broad low pressure area...currently located over the eastern Dominican Republic...is becoming better defined. However...the associated showers and thunderstorms are poorly organized at this time due to upper-level westerly winds. Conditions are expected to become more favorable for development... and the center of the low is expected to move into the Atlantic north of the Dominican Republic during the next 24 hours. Therefore...this system could become a tropical depression at any time as it moves slowly northwestward over the next couple of days. Regardless of whether or not this system becomes a tropical depression...it will continue to produce very heavy rainfall over Puerto Rico...the U.S. And British Virgin Islands...and the Dominican Republic through Monday. These rains could cause life-threatening flash floods and mudslides.
Interests in Puerto Rico...the U.S. And British Virgin Islands...the Dominican Republic...Haiti...the Turks and Caicos Islands...and the southeastern Bahamas should monitor the progress of this system and any products issued by their respective weather forecast offices.
Expect heavy rains of up to 10-15 inches to affect the eastern Dominican Republic today through Wednesday from this slow moving storm. Since most of 93L's heavy thunderstorm activity is on its east side, it currently appears that Haiti and the southeastern Bahamas will see less rain, perhaps 3-6 inches.
The intensity forecast
Wind shear is marginal for development, about 15-20 knots. Shear is forecast to drop to 5-10 knots Tuesday and Wednesday which should allow 93L to intensify into a 50-60 mph tropical storm. There is a window of opportunity for it to reach Category 1 hurricane strength before Friday, when it crosses north of Virginia (assuming it doesn't make landfall in North or South Carolina). Wind shear is forecast to increase to 15-20 knots and water temperatures will cool below 26°C on Friday, which should induce weakening.
The track forecast
The models agree on a slow west-northwesterly motion for 93L today, with a turn to the northwest or north-northwest on Tuesday. An extratropical storm is expected to develop off the coast of South Carolina by Wednesday, and five of our six reliable models predict that 93L and the extratropical storm will rotate cyclonically around a common center (the Fujiwhara effect), sending 93L hurtling into the U.S. East Coast on Friday somewhere between North Carolina and Massachusetts. The outlier is the UKMET model, which predicts that 93L will absorb the energy that would have gone into creating the extratropical low. 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. Considering that we are trying to forecast a complicated interaction between two storms that have yet to form, the current model forecasts for 93L are highly uncertain. Residents along the entire U.S. East Coast from Georgia to Maine should anticipate the possibility of a strong tropical storm affecting them by Friday.
Links to follow
Dominican Republic radar
Puerto Rico radar
San Juan, Puerto Rico weather
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