16B.1 Comparing the Path, Structure, and Intensity Associated with Hurricanes Matthew and Irma to the Local Impacts across Northeast Florida and Southeast Georgia

Friday, 20 April 2018: 11:00 AM
Masters ABCD (Sawgrass Marriott)
Nathaniel McGinnis, NWSFO, Jacksonville, FL; and B. Nelson

Over the course of two tropical seasons, northeast Florida and southeast Georgia experienced considerable impacts associated with Hurricane Matthew in October of 2016 and Hurricane Irma in September of 2017. After exiting the Bahamas as a category 4, 130 mph hurricane, Matthew gradually weakened as it moved up the east coast of the Florida Peninsula. The center remained 30 to 50 miles off the Florida-Georgia coast before making landfall in South Carolina as a category 1, 75 mph hurricane. Eleven months later, Hurricane Irma entered the Florida Straits as a category 4, 130 mph hurricane, before making landfall in the Florida Keys. Irma then made landfall in Naples, Florida as a category 2, 110 mph hurricane, and continued up the peninsula, weakening to a tropical storm 35 miles southwest of Gainesville.

Despite avoiding direct landfalls in northeast Florida and southeast Georgia, both Matthew and Irma brought substantial tropical cyclone conditions to the area. However, the severity of the hazards experienced were directly associated with the path and structure of the hurricanes, not the category as derived from the sustained wind speeds. For reference, at the closest path of approach, Matthew was a 120 mph hurricane positioned 50 miles east of Jacksonville, much stronger and closer to Jacksonville than Irma, which passed 85 miles west of Jacksonville as a 65 mph tropical storm. With Matthew’s track east of the Florida peninsula, the majority of impacts, such as storm surge, strong winds, and inland flooding, were located primarily along and near the coast. The larger size and western track of Irma equaled or exceeded the hazards experienced during Matthew and over a broader area.

The impacts from Irma were surprisingly substantial for a system that reached northern Florida as a strong tropical storm. Flooding rains between 5-15+ inches pushed inland rivers over the record levels from Hurricane Dora in 1964. Combined with rainfall run-off, many of the river gauges along the St. Johns River peaked near or above the previous records set by Dora and Matthew. Even the coast witnessed water levels associated with storm surge near or above Matthew. Matthew and Irma both produced storm surge not associated with a hurricane landfall in northeast FL, confirming the importance of separating the storm surge watch/warning product from the hurricane watch/warning product. With the western track of Irma, six tornadoes occurred, while zero were verified with Matthew. Lastly, with the broad wind field accompanying Irma, a more expansive area experienced tropical storm force winds with hurricane force wind gusts. By comparing Matthew and Irma, it will be shown that the impacts over the local area were unique to the structure and the path despite the vast intensity differences.

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