October Hurricanes in the Florida Keys

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True hurricane-force winds are rare, even in the Florida Keys, an especially hurricane-prone region, historically. An examination of hurricane tracks over the last century and a half indicates that the center of a hurricane passes within 125 nautical miles of the Keys, on average about once every two and a half years. Since the mid-1800s, hurricanes have affected the Florida Keys in each of the six months that make up the hurricane season. However, truth be told, over 70% of all hurricanes that have swept through or near the Keys have occurred during the two months of September and October. In fact, more hurricanes have traveled through the Florida Keys or adjoining coastal waters during October than in any other month! This may not seem readily apparent to those born during the latter half of the 20th Century or early part of the 21st Century because recent decades have been mostly free of October hurricanes. In fact, only three October hurricanes have affected the Florida Keys since 1970: Floyd (1987); Irene (1999); and Wilma (2005). However, five October hurricanes affected the Keys during the 1870s, with another five recorded in the 1940s. The decades of the 1900s, 1950s, and 1960s each tallied three October hurricanes. Between the end of the Civil War and 2005, a total of 27 October hurricane tracks have come within 125 nautical miles of Key West.

Further analysis of the historical hurricane data indicates that most of these October hurricanes (over 90%) formed over the Caribbean Sea, with a large majority (about 74%) forming over the southwestern or western Caribbean. A typical October hurricane scenario involves a mass of disorganized thunderstorms festering for several days over the southwestern Caribbean Sea before abruptly making the transition to tropical cyclone. Subsequent intensification into a hurricane may require one or more additional days over the deep, warm waters of the western Caribbean. Thereafter, the large, violent, oceanic whirlwind travels generally northward, often threatening the Cayman Islands, Cuba, or the Caribbean coasts of Honduras, Belize, or Mexico. It is over the northwestern Caribbean where October hurricanes are most likely to stall, loop, or make otherwise abrupt changes in forward motion. Here the atmospheric steering currents of the Tropics and the mid-latitudes meet and interact. Invariably, the stronger, undulating mid-latitude steering winds, powered by the increasing autumnal thermal contrasts between the Tropics and the Poles, win out over the weaker steering winds to the south. The hurricane in our scenario then is drawn northward, followed by a turn and acceleration toward the northeast, with the Florida Keys in its path. Both research and experience suggest that many October hurricane paths near the Keys evolve in a way indicated in the scenario described. All recorded October hurricanes affecting the Florida Keys traveled through the Keys during the first 25 days of the month. Therefore, it seems that a hurricane impact is less likely in the Keys during the last week in October, at least based on past observations. Indeed, a “Halloween hurricane” has yet to be observed in the Keys. Hurricanes threaten Florida Keys island communities with a variety of hazards, including violent winds and treacherous seas, storm-surge flooding, tornadoes, and torrential rains. Impacts from all such hazards have occurred in the Keys as a result of visits by October hurricanes, with corresponding loss of life, property, and infrastructure resulting in devastation to families and livelihoods. We cannot prevent occasional encounters with hurricanes in the Florida Keys. However, we can make our communities safer, and lessen the hurricane impact through mitigation, planning, and preparation. The time to think, plan, and act is now, before the next festering October tropical disturbance over the Caribbean Sea begins to organize, intensify, and move north. If you live or work in the Florida Keys, time spent planning and preparing for hurricanes is time well invested. As always, be weather-ready, and stay safe!