Wednesday, August 11, 2021

Tropical Storm Fred (2021)

Storm Active: August 10-14, 15-18

Around August 1, a tropical wave left Africa and entered the Atlantic. The wave did not develop much over the following 6 days, as conditions were not favorable and there was another wave closeby to the east. A few hundred miles east of the Windward Islands, the disturbance won out over its neighbor and developed a broad low-pressure center. By August 9, the system was located just north of Barbados. It moved west-northwestward into the Caribbean soon after. The circulation was quite impressive on satellite imagery: it had well-defined banding features and a clear spin. Nevertheless, it wasn't until that night that a center of circulation formed and it was upgraded to Tropical Storm Fred south of Puerto Rico.

Fred was dealing with dry air to its west, but its immediate problem was land interaction. After missing Puerto Rico to the south, the storm hit Hispaniola directly on the 11th, passing directly over the center of the island by that evening. The circulation was significantly disrupted and Fred weakened to a tropical depression. Though the cyclone was back over water overnight, there was some wind shear out of the west and it left most of its thunderstorm activity behind. It took most of the day on August 12 for Fred to slowly recover as it paralleled the northern coast of Cuba.

More land soon interrupted this reorganization, as Fred moved over central Cuba the next day. In fact, the low-level circulation became impossible to locate by that evening. Sometime soon after, Fred degenerated into a trough of low pressure and ceased to be a tropical cyclone temprorarily. However, heavy rains were still widespread across the region, so this changed the overall imapcts little. The system's remnants moved west-northwestward into the Gulf of Mexico on August 14 and began to organize again. The wind shear was a bit more favorable and ocean temperatures were warm as ex-Fred rounded the edge of the subtropical ridge and moved north-northwestward well west of Florida. On August 15, the circulation closed off and the system regained tropical storm status.

At first, the center was exposed on the western edge of the convection, but a semicircular core blossomed that evening and Fred began to strengthen. This trend continued through the morning of August 16 and Fred turned just east of north. By that time, the storm had a classic "comma" appearance, with a large curved band on the east side and a dry slot just southeast of the center. Some dry air intrusion via this slot capped Fred's intensity, but it still managed to become a strong tropical storm with top sustained winds of 65 mph before its final landfall in the Florida panhandle that afternoon. After landfall, the cyclone weakened steadily but brought a wide swath of heavy rain to the U.S. southeast and up the Appalachians. On August 17, Fred weakened to a tropical depression as it accelerated north-northeastward.

The storm continued to bring severe weather northward and eventually transitioned into a post-tropical storm over West Virginia the next day. Even after becoming post-tropical, ex-Fred brought severe weather into New England. It finally dissipated around August 19.



The above image shows Fred at peak intensity just before landfall in the Florida panhandle.


Fred's intensity was kept in check by land interaction for most of its lifetime.

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