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Omar steadily strengthening

By: Dr. Jeff Masters, 7:45 PM GMT on October 15, 2008

Hurricane Omar is steadily intensifying as it heads northeast towards an encounter with the Virgin Islands and northern Lesser Antilles early Thursday morning. The latest center fix from the Hurricane Hunters at 3:23 pm EDT put Omar's pressure at 973 mb, a 12 mb drop in six hours, and a drop of 5 mb in just the past two hours. The surface winds measured by the SFMR instrument were in the 85-90 mph range. Omar's current rapid pressure fall will lead to an increase in winds to Category 2 strength late tonight. The Hurricane Hunters noted that the eyewall was open to the southwest, and this is also apparent by examining Puerto Rico radar (Figure 1). Omar is still having trouble with wind shear of 15 knots from the west, and the eye has been visible only intermittently today. It appears that Omar is trying to build a new eyewall inside the current eyewall. It is unlikely Omar will be able to reach Category 3 strength until after this new eyewall is built, a process that will probably not be complete until after the hurricane passes through the islands.

Figure 1. Current radar image of Omar.

The forecast for Omar
There is no change to the forecast track, with the models tightly clustered along a path that would take Omar through the Virgin Islands early Thursday morning. Wind shear is about 15 knots, and is forecast to remain in the moderate 10-20 knot range until landfall. This should allow steady strengthening for the remainder of today. Some dry continental air has arrived on the northwest side of Omar, and I expect that this dry air will begin to penetrate into the vortex by early Thursday morning, slowing down intensification. The latest 12Z (8 am EDT) intensity forecasts from the various models have quite a spread, with the HWRF forecasting a 70 mph tropical storm at landfall; the SHIPS model, a Category 2 hurricane with 100 mph winds; and the GFDL model, a borderline Category 2 or 3 hurricane with winds of 110-115 mph. The official NHC forecast of a Category 2 hurricane at landfall seems like the best compromise. There is about a 20% chance Omar will be a Category 3 hurricane at landfall.

Links to follow
Puerto Rico radar
Eastern Caribbean buoy 42059
San Juan, Puerto Rico weather
St. Croix, Virgin Islands weather
Martinique radar

Tropical Depression 16 off the coast of Honduras
There has been little change to Tropical Depression 16, near the Honduras/Nicaragua border. Satellite loops show that TD 16 is a very large but poorly organized storm, with several far-flung spiral bands that are spreading heavy thunderstorms over a wide area of the Western Caribbean and Central America. The center of circulation is broad and difficult to pin down, but appears to be over the water, within 50 miles of the coast of Honduras.

The forecast for TD 16
The system is expected to track very close to the coast of Honduras, and this proximity to land should limit intensification potential. None of the models are calling for TD 16 to become any stronger than a 40 mph tropical storm. Given the storm's current disorganization, I doubt that it will ever become a tropical storm. However, the depression is going to bring potentially dangerous amounts of rainfall capable of causing flash flooding and mudslides.

Hurricane Ike relief efforts
There continues to be an urgent need for relief supplies in the wake of Hurricane Ike. I recommend contributions to the portlight.org charity fund, formed by wunderground memebrs to serve the needs of those often bypassed by traditional relief efforts. Contributions are fully tax-deductible, and more details can be found at StormJunkie's blog.

Jeff Masters
ts omar aruba
ts omar aruba

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.