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Tomas significantly weaker; damage very heavy on St. Lucia and neighboring islands

By: Dr. Jeff Masters, 6:38 PM GMT on October 31, 2010

Hurricane Tomas dealt a punishing blow to the Caribbean island of St. Lucia, with the neighboring islands of St. Vincent, Dominica, and Barbados also suffering heavy damage. St. Lucia received the full brunt of the northern eyewall of Tomas as it intensified into a Category 2 hurricane with 100 mph winds early this morning. The St. Lucia weather service reported that sustained winds of 90 - 95 mph affected the island. A state of emergency has been declared on the island, and there are island-wide power outages on both St. Lucia and Dominica. Heavy flooding affected St. Lucia, washing out many bridges, and the airport is closed due to flooding. Damage to structures is considerable, with many roofs gone, and damage reported to hospitals, schools, and businesses.

Figure 1. Torrential rains from Tomas triggered massive flooding on St. Lucia that destroyed several bridges and severely damaged roads. Image credit: Caribbean Hurricane Network.

Tomas significantly weakens
An Air Force hurricane hunter aircraft arrived at Tomas at 2pm this afternoon, and found a much weaker storm. The 2pm EDT center fix found that the pressure has risen to 994 mb, and the strongest surface winds were barely Category 1 hurricane strength, 74 mph. The aircraft found the the eyewall had mostly collapsed. Satellite loops of Tomas also show a significant degradation in the appearance of the storm in recent hours. The storm is highly asymmetric with very little heavy thunderstorm activity or upper level outflow on the west side, and the hurricane has only one prominent spiral band, on the east side. Wind shear is a high 20 knots due to strong upper level west-southwest winds, and these winds are driving dry air at mid-levels of the atmosphere into Tomas' west side, as seen on water vapor satellite imagery.

Figure 2. MODIS satellite image of Tropical Storm Tomas taken at 10:30am EDT Saturday October 30, as the storm began lashing the Lesser Antilles. At the time, Tomas was a Category 1 hurricane with 75 mph winds. Image credit: NASA.

Track forecast for Tomas
The ridge of high pressure pushing Tomas to the west-northwest will weaken by Tuesday, as a trough of low pressure approaches the eastern U.S. and breaks down the ridge. This will result in Tomas slowing from its current 9 mph forward speed to 5 mph by Tuesday. By Thursday, the trough to Tomas' north should be able to pull the storm to the north. The exact timing and location of this turn is still very uncertain. The computer model solutions from the latest set of 8am EDT (12Z) runs include a strike on Haiti on Friday (GFS and GFDL models), a strike on the Dominican Republic on Friday (NOGAPS model), a strike on Haiti on Saturday (UKMET model), a strike on Jamaica and eastern Cuba on Thursday (Canadian), or a strike on Puerto Rico on Friday (HWRF).

Intensity forecast for Tomas
Wind shear is forecast to remain in the high range, 20 - 25 knots, through Monday night, then decline to the moderate range, 10 - 20 knots, for the remainder of the week. Tomas will struggle with the shear and the dry air to its west through Tuesday, and I expect it will weaken to a tropical storm tonight, and remain a tropical storm until Tuesday, when the shear finally relents. At that point, re-intensification is likely, though with the storm's inner core gone, I expect it will take Tomas two days before it can re-establish a complete eyewall. Hindering that process will be the slow motion of the storm, which will allow cooler waters from the depths upwell to the surface and cool the SSTs. Still, the waters are very warm in the Caribbean and these waters extend to great depth, so the upwelling cool water may not impede intensification as much as might ordinarily be expected. The intensity Tomas might have as landfall in Hispaniola or Jamaica is highly uncertain, and a strength anywhere between a tropical storm and Category 3 hurricane would not be surprising. The HWRF model predicts Tomas will be a borderline tropical storm/Category 1 hurricane on Friday, while the GFDL foresees Tomas will be a strengthening Category 3 hurricane as it bears down on Haiti Friday afternoon. I predict Tomas will have trouble reorganizing, and will be a strengthening Category 1 hurricane on Friday as it makes landfall in Haiti or the Dominican Republic.

Figure 3. Hurricane specialists Robbie Berg (background) and Dan Brown (foreground) discuss the latest data on Tomas Friday night at the National Hurricane Center.

Next update
I'll have an update Monday morning.

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.