Tropical Storm Isaias - August 1-2, 2020

Summary

Tropical Storm Isaias formed in the eastern Caribbean Sea on Wednesday evening, July 29th, and moved NW across Hispaniola on Thursday, July 30th. Isaias continued on a NW track and became a hurricane at Midnight on July 31st near Great Inagua Island, then moved over Andros Island on Saturday, August 1st when it was then downgraded to a Tropical Storm with maximum sustained winds of 70 mph. TS Isaias then made a gradual turn to the N-NW as the center passed about 30-40 miles east of the Palm Beach County coast (its closest approach to the SE Florida coast) on Sunday, August 2nd.

Isaias did not regain hurricane strength as it passed just east of the SE Florida coast for what appeared to be two main reasons: 1) strong W upper level winds which caused the thunderstorms near the center of the storm to be sheared off to the east and not around the surface circulation, and 2) relative dry tropospheric air over Florida to the west of the storm. This caused Isaias to have a highly asymmetrical structure with the strongest winds and heaviest rainfall well to the east over the Bahamas, with limited extent of tropical storm force winds and rainfall on the west side. Isaias eventually regained hurricane strength just before landfall near Wilmington, NC on August 3rd, then continued NE over the U.S. eastern seaboard as a fast-moving tropical storm. 

                                                         Track image courtesy of Hurrevac

                                                     Satellite image from Sunday, August 2nd at 7:30 AM EDT. Courtesy RAMMB/CIRA

South Florida Watches and Warnings

A Tropical Storm Watch was issued for SE Florida at 5 PM Thursday, July 30th. At 11 PM on the 30th, it was expanded westward to include Lake Okeechobee. A Tropical Storm Warning was issued for SE Florida at 11 AM on Friday, July 31st, and a Hurricane Watch was also issued for Broward and Palm Beach counties at that time. The Hurricane Watch was upgraded to a Hurricane Warning at 5 PM, Friday July 31st for the Palm Beach County coast and northward to the Volusia/Brevard County line. 

The Hurricane Watch for Broward County was discontinued at 5 PM Saturday, August 1st, with the Tropical Storm Warning remaining in effect. The Hurricane Warning for Palm Beach County was downgraded to a Tropical Storm Warning at 5 AM Sunday, August 2nd, and the Tropical Storm Warning was discontinued for Miami-Dade County. As of 5 AM Sunday, August 2nd, only a Tropical Storm Warning remained for Broward and Palm Beach counties. At 11 AM Sunday, August 2nd, all tropical storm warnings were discontinued from Palm Beach County south. 

Data

The westernmost extent of sustained tropical storm force winds reached the SE Florida coast during the early morning hours of Sunday, August 2nd, as evidenced by a sustained wind reading of 36 knots/41 mph at Lake Worth Pier at 6:36 AM. Sustained tropical storm force were likely limited to the coastline, with very little inland extent. Gusts to tropical storm force began affecting the SE Florida coast during the mid afternoon hours on Saturday, August 1st, and this is when the highest wind gust associated with Isaias in South Florida was recorded (58 mph at Dania Pier at 2:22 PM) in association with a heavy squall moving onshore well ahead of Isaias. 

Rainfall was similarly limited on the west side of Isaias. The highest recorded rainfall total for the 72-hour period ending at 8 AM Monday, August 3rd was 2.60 inches by a WeatherBug station on Miami Beach. Most locations recorded less than 2 inches for the entire event.

Highest wind gusts and rainfall totals for select locations are listed below. A full summary of data can be found via the Isaias Post Storm Report for South Florida. 

Impacts

Wind and flooding impacts were minor across South Florida. Almost 3,000 customers lost power during the event, almost all of them in Palm Beach County. Beach erosion was most notable along the northern Palm Beach County coast, with minor beach erosion as far south as northern Broward County.