Fiona (the sixth Atlantic tropical cyclone of the 2016 season) recently passed. In her wake, Gaston briefly reached hurricane strength far out in the Atlantic. Another tropical system (99L) near the Bahamas is still showing signs of intensifying this weekend as it approaches the Florida Straits. And, more African waves seem ready to exit the west African coast and join this Atlantic train of tropical weather systems. All this as the peak of hurricane season (Sept. 10) looms.
For obvious reasons, the potential system nearing the Bahamas brings the greatest concern. During the past two days, National Hurricane Center (NHC) forecasters have begun to downplay chances for tropical storm or tropical depression formation (although, anytime a system like this is near the U.S., it warrants close scrutiny).
However, the bigger threat seems to be heavy rainfall and rip currents. The persistent strong easterly wind flow (and the expected elevated wind speeds as the system approaches later this weekend) will allow for rip currents to develop along east-facing beaches across much of the so-called Sunshine State. I say, “so-called,” because extensive cloud cover and widespread precipitation areas (filled with heavy showers and thunderstorms) will make folks wonder if the sun even exists. The Naples area forecast, for example, keeps mostly cloudy skies as the main sky condition until next Thursday. If the sun does peak out of thick, multi-layered clouds, it will likely be for very short periods, at best.
NOAA’s Weather Prediction Center (WPC) has issued its latest quantitative precipitation forecast (QPF) for the seven-day period ending next Friday. This places much of Florida in a five to seven inch rainfall zone (Fig. 1). As always, local amounts can often be double the expected general rainfall numbers.
Much of the southern half of Florida is already reporting above average yearly rainfall (Fig. 2). Some places are as much as fifty percent or more above average. Fort Myers, for example, is already nearly 12 inches above its yearly average rainfall of 36 inches through Aug. 25. Additional rainfall will only add to water management issues across the southern part of the state, including increased agricultural and fertilizer runoff (which contribute to the development of algal blooms in near-shore Gulf waters).
Since sand is the dominant ground material in south Florida’s (not clay soil like Louisiana), any localized heavy rainfall will not likely generate massive flooding. However, normally poor drainage areas, places with storm sewer gratings filled with leave sand twigs and even some urban areas can expect ponding of water on roadways and in low-lying areas. Coastal urban flooding will be exaggerated if heavy rain falls during the time of high tides.
The best advice for now is to keep up-to-date on the tropical activity near Florida, and be very cautious of any heavy rainfall and localized ponding water, especially while driving.
© 2016 H. Michael Mogil
Originally posted 8/26/16