TD 27 still battling strong shear

Wind shear from strong upper-level westerly winds has disrupted Tropical Depression 27 this afternoon. The depression was probably near tropical storm strength for a few hours late this morning, but since that time, the center of circulation has become more exposed, and the deep convection has retreated to the southeast side. The spiral band that had formed to the south is gone now. Wind shear is continuing to drop, and is now in the 15 - 20 knot range. This shear is still high enough that there remains a 10% the depression will dissipate within the next 48 hours. If the storm can survive until past then, the shear will decrease enough to allow TD 27 to strenghen into a tropical storm and remain in a threat to the Caribbean for the rest of the week.

The eventual intensity of TD 27 is highly uncertain, and will be highly dependent on the track of the storm. If TD 27 can position itself under an upper-level anticyclone that is expected to develop by Wednesday over the central Carribean, the storm has a chance to attain hurricane status. Ocean temperatures are 28-29C--plenty warm enough to allow a hurricane to form. The GFDL model still predicts TD 27 will intensify into a major Category 3 hurricane by the end of the week. However, the other major intensity model, the SHIPS model, forecasts a strong tropical storm by the end of the week. There is no way to tell now which model is more likely to be correct.

The computer models agree on the basic idea that TD 27 will track westward over the Caribbean for the next five days, under the steering of a strong ridge of high pressure. By the end of the week, the models begin to diverge.
The GFDL and NOGAPS depict a stronger system and show a threat to Jamaica, while the GFS and UKMET have a weaker system farther south that is more of a threat to Honduras and Nicaragua. None of the models show the storm moving far enough north to get caught in the westerly winds prevailing over Cuba and getting recurved out to sea. It appears that the ridge of high pressure steering TD 27 westwards will continue to hold in place for at least seven days, making Honduras the most at-risk area for a strike. Remember, a lot can change with forecasts for the large-scale weather patterns five to seven days from now, and the future track that far in advance will depend heaviy on how intense the storm becomes.

The Hurricane Hunters are scheduled to make their first flight into TD 27 Tuesday afternoon.

I'll be back with an update in the morning, unless TD 27 gets a name tonight. Incidently, TD 27 is only the 3rd tropical depression in history to form in November in the eastern Caribbean.

Jeff Masters