Weather Nerd

Omar now a hurricane, heading for Virgin Islands

Tropical Storm Omar became a hurricane at 11:00 PM EDT last night, and at that time, it appeared likely to continue strengthening overnight. But wind shear disrupted the storm somewhat this morning, slowing its intensification. If not for the shear, we could be looking at a Category 2 or even 3 hurricane by now.

Now, however, as of 11:00 AM EDT, it appears Hurricane Omar is strengthening again. Top sustained winds are up to 85 mph, and are forecast to reach 105 mph — enough for Category 2 status — as the storm passes through the Virgin Islands tomorrow morning.

Omar is actually expected to make its initial landfall (or near-landfall) at St. Croix very late tonight or very early tomorrow — around midnight, give or take a few hours — and then continue northeastward toward the rest of the Virgin Islands. It will be exiting the islands by around 8:00 AM EDT, which is when the NHC forecast calls for 105 mph winds.

Here’s what the NHC’s 11am discussion says about the potential for further strengthening:

NOW THAT A DISTINCT EYE AND EYEWALL HAVE DEVELOPED…A GOOD CHIMNEY EFFECT CAN BE ESTABLISHED AND OMAR COULD GO THROUGH A BRIEF PERIOD OF RAPID INTENSIFICATION AGAIN.  ONLY THE GFDL MODEL IS CALLING FOR OMAR TO STRENGTHEN TO AT LEAST 90 KT.  THE REMAINDER OF THE INTENSITY GUIDANCE HOLDS OMAR BELOW 80 KT.  BASED ON THE BETTER DEFINED EYE FEATURE…AND THE FACT THAT OMAR IS A RELATIVELY LOW SHEAR ENVIRONMENT AND OVER 29C AND WARMER SSTS…ADDITIONAL INTENSIFICATION SIMILAR TO THE GFDL MODEL SEEMS QUITE REASONABLE.  IT ALSO ISN’T OUT OF THE QUESTION THAT OMAR COULD ACHIEVE MAJOR HURRICANE STATUS JUST BEFORE THE CYCLONE REACHES THE NORTHERN LEEWARD ISLANDS.  HOWEVER…THE RAPID ENCROACHMENT OF DRY MID-LEVEL AIR FROM THE NORTHWEST AS NOTED IN WATER VAPOR SATELLITE IMAGERY PRECLUDES EXPLICITLY FORECASTING THAT INTENSITY AT THIS TIME SINCE THAT DRY AIR COULD MAKE IT INTO THE INNER CORE REGION IN 12-18 HOURS AND WEAKEN THE HURRICANE.

Dr. Jeff Masters, in a post published shortly before the 11am advisory came out, writes:

The models are tightly clustered along a path that would take Omar through the Virgin Islands late tonight. However, the east coast of Puerto Rico and the islands farther east, such as St. Martin/St. Maartin and Anguilla, are still in the cone of uncertainty, and could get a direct hit. Our main intensity models–the GFDL, HWRF, and SHIPS–all forecast that Omar will be a Category 1 hurricane with winds of 75-85 mph as it passes through the islands. Wind shear is expected to be in the moderate to high range, 15-25 knots, over the next two days, which should allow some modest intensification. I give Omar a 30% chance of reaching Category 2 strength before landfall early Thursday morning, and a 10% chance of being a major Category 3 hurricane.

You can follow the storm’s progress on long-range San Juan radar.

Meanwhile, it now appears less likely that Tropical Depression 16 will become Tropical Storm Paloma. The system’s ill-defined center has moved ashore, or nearly so, in Honduras. There is still a chance it could become a minimal tropical storm as it meanders westward, but that is mostly a technicality. This will be a rain-maker but nothing more.