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Tomas a Potential Threat to Haiti & Jamaica

Posted by Andy Johnson under Daily updates

The areal extent of heavy convection associated with Tropical Storm Tomas has continued to increase today as the overall environment surrounding the storm becomes more moist. The appearance of the convection is not circular or banded so there does not appear to be more organization taking place. A hurricane reconnaissance plane is investigating the storm Tuesday afternoon and as of 2:30 PM had not found a strengthening system yet. However, with less shear, a very moist environment and near record warm water temperatures, all indications are that Tomas will re-strengthen and will likely become a hurricane once more.

Haiti has the highest probability of a direct strike at this point in time, followed by Jamaica and the Dominican Republic. All of the the large scale models have been showing a deep trough moving eastward towards the U.S. East Coast and then continuing out to sea, which would turn Tomas to the northeast. In the longer time range period, the deep trough begins to lift out by this weekend. As a result, Tomas will be left in an area of weaker steering currents. In addition, by the weekend a ridge of high pressure in the upper atmosphere will begin building over the U.S. East Coast replacing the trough. The end result it that Tomas could slow down by the weekend and cause torrential rains wherever it slows down. This could occur west of Haiti or north of Haiti near the Turks and Caicos or even out at sea. The worst case scenario would be for Tomas to slow down in forward speed just to the west of Port-au-Prince, Haiti. Remember that there are still thousands of people displaced from the January earthquake which devastated the region. In addition, many of the mountains to the east of  Port-au-Prince have been deforested. As a result, even if hurricane force winds do not occur, the potential for mudslides and flooding is of great concern. If hurricane force winds occur where many people are living in tents and makeshift structures, there could be great loss of life.

The radar image below is from the Curacao radar taken Tuesday afternoon. The rain areas do not appear very organized on radar. There is a large separate area of rain each of the A,B, C Islands (Aruba, Bonaire and Curacao) that is not near the center of circulation. This pattern has existed with Tomas for several days with a separate area of convection that trails to the east of the storm. This phenomenon is likely due to the southwesterly shear which has existed for a few days causing some moisture to be displaced east of the center.

The enhanced satellite image belows shows a much larger overall cloud cover with Tomas but it does not have a classical circular or comma shaped appearance. The clouds in the western Gulf are part of the trough which is moving east and expected to turn Tomas towards the northeast. A tropical wave in the eastern Atlantic shows no signs of intensifying at the present time.

A close-up satellite view of Tomas (shown below) indicates a ragged appearance to the convection associated with the tropical storm.

Wave height in the eastern Caribbean have decreased to 7.5 feet as Tomas has moved farther away in the southern part of the Central Caribbean.

 Some of the models such as the BAMS and NOGAPS (shown below) forecast Tomas to greatly slow down in speed by the weekend which could produce a long period of heavy rain over Haiti.

The GFS model forecast valid at 8:00 PM Thursday shown below indicates an East Coast trough picking up Tomas and turning him to the northeast.

However, note that by Monday at 7:00 AM, the trough has lifted out leaving Tomas in its wake and a strong ridge over the East Coast has replaced the trough. That scenario could slow the forward speed of Tomas or turn him south or even west.