Tropical Storm Chantal (2013)

Storm Active: July 7-10

During the first days of July, a tropical wave moved off of the coast of Africa and tracked rapidly westward. By July 5, concentrated thunderstorms had appeared in a association with a low pressure area at the southern tip of the tropical wave as it moved through the central Atlantic. Initially, development was not anticipated due to the timing: in early July, the central Atlantic does not often support tropical development, partially due to Saharan dry air dominating the region. However, the system remained exceptionally far south, between 5° and 10°N latitude, and it was isolated from the strong shear to its north.

On July 7, satellite data indicated the imminent development of a closed circulation in association with the wave as the low pressure system gained definition. Late that evening, the low was designated Tropical Storm Chantal, as it was observed to have tropical storm force winds. At the time, Chantal was tracking rapidly westward, at speeds in excess of 25 mph, embedded as it was in strong steering winds. During the day of July 8, Chantal's winds steadily increased and its circulation became better defined, but the convective organization remained quite ragged as strong subtropical ridges continued to steer the storm west to west-northwest.

On July 9, showers and thunderstorms began to impact the Windward Islands as the cyclone passed through. Bursts of thunderstorm activity flared up periodically throughout the day, and Chantal continued its trend of modest strengthening, managing to maintain its circulation despite its forward velocity. The system reached its peak intensity of 65 mph winds and a pressure of 1005 mb. However, that evening, increasing westerly shear finally began to take its toll, decoupling the tropical storm's circulation from the surrounding shower activity. By late that evening, nearly all convection had vanished, and the center was nearly impossible to identify.

While it appeared as though Chantal had lost its circulation entirely and degenerated into a tropical wave, rapid development of thunderstorm activity occurred during the morning of July 10 and a poorly defined circulation was found. The system also had made a turn back to the west, indicating a shallow circulation. Indeed, the pressure had risen and Chantal had weakened to a low-end tropical storm. However, heavy rain, mostly displaced to the north and east of the center, swept over much of Hispaniola that afternoon as the storm passed to the south. Finally, additional evidence emerged during the evening of the same day that the circulation had indeed disappeared, and advisories were discontinued as Chantal degenerated into a tropical wave.

A low pressure trough associated with the remnants of Chantal was still producing a large area of thunderstorms on July 11 as it drifted northwestward over eastern Cuba and into the Bahamas. Over the following two days, the disturbance continued to cause rainfall in the Bahamas, and eventually in parts of the U.S. southeast coast, but it did not show any signs of development, and on July 13 merged with a larger system to its north.

The above image shows Chantal, not at peak intensity, but perhaps at peak convective organization before it entered the Caribbean.

Chantal moved at a blistering pace before dissipating in the Caribbean. The final points on the track (triangles) show its progress as a disturbance over Hispaniola and Cuba, where it caused widespread flooding.