Tropical Storm Chantal could impact Florida, Southeast U.S.

July 9, 2013

Tropical Storm Chantal’s satellite appearance is decidedly less organized today, but she is still a significant threat to the Caribbean over the next few days, and must be watched for potential impact on the Southeast U.S. late this week into early next week.


Enhanced satellite image of Chantal at 8:15 a.m. EDT today, just about to enter the Caribbean Sea. (NOAA)

At 11 a.m. EDT, Chantal’s maximum sustained winds are estimated at 60 mph, and she is still moving very quickly to the west-northwest at 29 mph. Hurricane Watches, Tropical Storm Watches or Tropical Storm Warnings are posted for the majority of islands bordering the eastern Caribbean, and you should consult the National Hurricane Center website for the latest advisories, watches and warnings. Another aircraft reconnaissance mission is investigating the storm this morning, so we’ll get additional accurate intensity fixes from that.

I have also created long radar loops from Barbados and Martinique to facilitate tracking the storm as it crosses the Lesser Antilles. When available, others will be added as Chantal comes into their range, so please check back later too.

Radar image from Barbados (in the center) showing Chantal's center passing about 40 miles north of the island and heading toward St. Lucia and Martinique in the Windward Islands.
Radar image from Barbados (in the center) showing Chantal’s center passing about 40 miles north of the island and heading toward St. Lucia and Martinique in the Windward Islands. (barbadosweather.org)

As Chantal continues to race forward she is running into stronger vertical shear (measured as the difference between the wind speed and direction at 5,000 feet versus about 38,000 feet). A tropical cyclone can thrive in shear below about 18 mph. Although Chantal is over very warm ocean waters, the shear is up to approximately 25 mph (largely due to its own motion) and is forecast to reach 30-35 mph by Friday before decreasing somewhat after that. Another substantial obstacle in its way is the mountainous island of Hispaniola, home to the countries of Dominican Republic and Haiti.

Chantal has until about midday Wednesday to strengthen, then it will pass over or very near Hispaniola, which is historically not very gentle to tropical cyclones with its extensive mountain ranges above 6,000 feet and some reaching to 10,000 feet (although due to its rapid forward speed, it won’t spend too long over the island). After that encounter, the low-level circulation often has to reform, but the Bahamas don’t offer any resistance to that, and it could begin to re-intensify by Thursday afternoon.

Then, the official forecast as well as many models agree that it will turn northwest in response to a trough over the eastern U.S. In the U.S., the first area to experience effects from the storm would be Miami and the southeast Florida peninsula, which at this point is forecast to be on the western periphery of the wind field, with just a slight chance of tropical storm force winds from Friday night into Saturday.

Beyond that, a subtropical ridge is forecast to build back in and gradually steer the storm more toward the west or west-northwest. That brings northern Florida up into South Carolina into play, with deteriorating conditions on Sunday and a possible landfall on Monday. At this point, it doesn’t look like it will be too strong, possibly a tropical storm or Category 1 hurricane. A lot rests on what the storm does after crossing Hispaniola and how quickly it can reorganize.

Five-day track forecasts from a variety of models. (It's worth noting that CLP5, BAMS, BAMM, BAMD, XTRP, and LBAR are not real dynamical models. (NCAR)
Five-day track forecasts from a variety of models. (It’s worth noting that CLP5, BAMS, BAMM, BAMD, XTRP, and LBAR are not real dynamical models.) (NCAR)

As a side note, Chantal is another one of the original names in the modern era of naming storms that began in 1979. Since there are six annual lists, and its first appearance was in 1983, this is the sixth reincarnation of Chantal. The collective tracks are shown below for reference.


Tracks for all six tropical systems named Chantal. (Brian McNoldy)

Elsewhere across the Atlantic basin, another noteworthy easterly wave is exiting the African coast today and is centered near 17W, or just off the coast of Senegal. Several global models favor the development of this, and it could possibly be our next tropical cyclone by the weekend. It is way too early for any in-depth discussion, but I’m watching it very closely! The next name on the list is Dorian — a new name this year that replaces Dean which got retired in 2007.

* Brian McNoldy is a senior researcher at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science.

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Ian Livingston · July 9, 2013