Gabrielle Getting Ripped Apart, Now a Tropical Depression

After a brief 12-hour life as a tropical storm, Gabrielle has weakened to a tropical depression as it moves northwest at 9 mph. Wind shear, dry air, and interaction with the rough terrain of Puerto Rico and a strong tropical disturbance to its northeast have significantly disrupted Gabrielle. The surface center of circulation is near the Mona Passage between Puerto Rico and the Dominican Republic, and is displaced about 150 miles to the west-southwest of the main area of heavy thunderstorms over the Virgin Islands, as seen on satellite loops. A strong tropical disturbance located about 300 miles to the northeast of Gabrielle pulled the mid-level circulation of Gabrielle into it, leaving the surface circulation behind. This tropical disturbance that helped pull Gabrielle apart is a threat to become a tropical depression on its own--NHC gave it a 20% chance of development in their 8 am EDT Thursday Tropical Weather Outlook. The disturbance is headed to the northwest into an area with high wind shear of 20 - 30 knots, so development is unlikely.

Heavy thunderstorms from Gabrielle dumped over two inches of rain over portions of the Virgin Islands and Southeast Puerto Rico as of 10 am AST Thursday. Heavy rains will continue today across Puerto Rico and the Virgin Islands, as seen on radar out of San Juan, Puerto Rico. Gabrielle did not generate any sustained winds of tropical storm force (39 mph) at any land stations.


Figure 1. Morning satellite image of Gabrielle showing the surface center displaced 150 miles to the west-southwest of the main heavy thunderstorms over the Virgin Islands.

Forecast for Gabrielle
Wind shear is expected to steadily increase as Gabrielle heads northwest over the next few days. The storm will also be encountering the high mountains of Puerto Rico and Hispaniola, which should act to further disrupt the circulation. The tropical disturbance to the northeast of Gabrielle will also act to pull it apart, and it appears likely that Gabrielle will dissipate by Friday morning, unless the surface center can reform underneath the heaviest thunderstorms 150 miles to the east-northeast of the surface center. Gabrielle or its remnants should begin heading to the north over the weekend, and may pass close to Bermuda next week.


Figure 2. Radar-estimated precipitation from Gabrielle as of 10:32 am AST September 5, 2013.

Elsewhere in the Atlantic
A tropical wave over the extreme Southwestern Gulf of Mexico's Bay of Campeche (Invest 99L) will move ashore on the Mexican coast near Tampico on Friday. Satellite images show that 99L has a moderate area of heavy thunderstorms that are slowly increasing in size and intensity. Wind shear is moderate and water temperatures are a warm 30°C, so 99L will likely show steady development until landfall on Friday. In their 8 am EDT Thursday Tropical Weather Outlook, NHC put the 5-day and 2-day odds of development at 30%. A hurricane hunter aircraft is scheduled to check out the disturbance Thursday afternoon.

A tropical wave in the Eastern Atlantic about 450 miles west-southwest of the Cape Verde Islands (Invest 98L) is headed west-northwest at about 10 mph. Satellite images show that 98L has a decent amount of spin, but a very limited amount of heavy thunderstorms. Wind shear is moderate and water temperatures are a warm 28°C, so 98L may show some slow development today and Friday. By Saturday, 98L will encounter drier and more stable air, and be over waters barely warm enough to support a tropical cyclone--26.5°C. In their 8 am EDT Thursday Tropical Weather Outlook, NHC put the 5-day and 2-day odds of development at 10%.

A strong tropical wave is predicted to emerge from the coast of Africa on Saturday, and the GFS model develops this wave into a tropical depression near the Cape Verde Islands by Monday. The storm is expected to track to the northwest into a region of ocean where very few tropical cyclones ever make the long crossing of the Atlantic Ocean to threaten North America. Both the GFS and European models predict that this system will develop into a hurricane next week. In their 8 am EDT Thursday Tropical Weather Outlook, NHC put the 5-day odds of development at 30%.

Jeff Masters