Caribbean disturbance a threat to Puerto Rico; Hawaii needs to keep an eye on the tropics

An area of disturbed weather (90L) over the northern Lesser Antilles Islands expanded significantly in size overnight, but has lost most of its heavy thunderstorm activity this morning. Wind shear is 10 knots over the disturbance, and is expected to remain below 10 knots for the next two or three days. Water temperatures are about 29 degrees C, which is plenty warm for a tropical cyclone. There is quite a bit of dry air to the west, which may distrupt any heavy thunderstorm activity that tries to form. Martinique radar shows considerable thunderstorm activity, but the activity is pretty disorganized at present. Winds in the northern Lesser Antilles Islands have been unspectacular so far today--no more than 15 mph at St. Kitts, St. Maartin, and Antigua. The morning pass of the QuikSCAT satellite missed 90L; we'll have to wait until about 9pm EDT tonight for the next pass. It is difficult to tell from satellite imagery or surface reports if 90L has a surface circulation. Due to the collapse of heavy thunderstorm activity this morning, it now appears unlikely 90L will become a tropical depression in the next two days.

Most of the computer models forecast a track over the northern Lesser Antilles Islands the next two days, with the disturbance moving over Puerto Rico Saturday morning and the Dominican Republic on Saturday night. The system is being drawn northwest by a strong trough of low pressure passing to the north of the islands. However, it appears that this trough is not strong enough to pull 90L out to sea, and high pressure should build in and force the storm westward by Sunday. The storm still has a chance to become a tropical depression early next week if it can avoid Hispaniola. However, wind shear is expected to rise over the Caribbean beginning on Sunday, and this may put an end to the threat.


Figure 1. Preliminary model tracks for disturbance "90L".

Hawaii
Residents of Hawaii should continue to watch an area of disturbed weather (97C) near 9N, 166W, about 1000 miles southwest of the Hawaiian Islands. A QuikSCAT satellite pass from 12:56am EDT this morning showed a closed surface circulation, and some wind barbs of 40-45 mph to the south of the center. The thunderstorm activity has gotten more intense over the past day, but is still disorganized. Wind shear has increased to about 15 knots today, but this is still low enough to allow some slow development. Sea Surface Temperatures (SSTs) are about 29C, and there is a very deep pool of warm water underneath to fuel intensification. Both the GFDL and NOGAPS models forecast that 97C will become a strong tropical storm or Category 1 hurricane that will threaten the Hawaiian Islands on Monday night or Tuesday.


Figure 2. Preliminary model tracks for disturbance "97C".

Elsewhere in the tropics
The models continue to show the possibility of a low pressure system forming in the Gulf of Mexico near the Texas coast early next week. This low will probably be non-tropical, though. Several models are calling for a tropical storm to develop along the Pacific coast of Mexico by Monday and move northwest towards Baja. Baja does not need to worry about Tropical Depression Olivia, which is expected to dissipate Friday before reaching Baja.

I'll have an update later today if 90L or 97C show significant change.

Jeff Masters