Fall is not only enjoyable in South Florida as it sees the humidity begin to break, but it is also when the tropics begin shutting down and the threat from hurricanes gets lower and lower.
Of course, fall weather arrives at different times on different years. Some years, storms are ripping well into November (as we saw just two years ago with 2020′s record season). Other years, the switch gets thrown a little sooner. The National Weather Service chose Oct. 15 as the fixed date for the end of rainy season in South Florida, as it has been shown as roughly the average date that fronts from the north have ushered in cooler, less humid air from the continental US. This air is also much more stable, and it offers much lower octane fuel that limits the ability for tropical disturbances to develop. Once this air begins regularly sweeping across South Florida, it often signals the threat from the tropics is wrapping up for the year.
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Though the threat is lower, it is not an “all clear.” Sometimes the fronts can get hung up over the still-warm waters, where clumps of storms can fester, find small pockets of favorable conditions, and develop into tropical systems. We watch those in Florida, because they tend to cruise along the fronts and can move in our direction.
Something else that comes along with the fronts to help neutralize the tropics is a shift to unfavorable upper level winds. Tropical systems are very sensitive to changes in wind speed and direction through the atmosphere, and a fall pattern has plenty of this as the jet stream dips further south. We certainly see that happening now.
Looking back over the past 100 years, the frequency of storms drops sharply after mid-October. The National Hurricane Center is not expecting any tropical formation through the next week, at least. Long range computer models are also quiet. It’s too early to call it, but for now at least, hurricane season is on break.
