At 10:21 Thursday morning, the sun gave itself equally to the Earth’s northern and southern hemispheres, marking the astronomical milestone of autumn.
Everything after is the downslope to winter — later sunrises, earlier twilights and cooler temperatures.
But not so fast on the thermostat plunge for South Florida.
The climatological clock runs four to six weeks late in the Sunshine State when it comes to welcoming the finer points of fall, namely its brisker temperatures.
“We are still in a summertime pattern, which is normal for us,” said Robert Molleda, warning coordination meteorologist for the National Weather Service in Miami. “The month of September in South Florida is still temperatures in the upper 80s and some days getting to 90.”
Wednesday’s high temperature in West Palm Beach was 91 degrees – three degrees above normal, with a heat index of 99 just after midday.
Noticeable temperature changes for Palm Beach, Broward and Miami-Dade counties don’t typically occur until mid-October, with the first occurrence of a 60-degree overnight low not arriving until Nov. 2 in West Palm Beach.
Belle Glade’s average first 60-degree temperature is Oct. 24, while Miami Beach has to wait until Nov. 17.
Rain, dew point temperatures and daily minimum temperatures all play a role in determining when summer officially ends, according to a National Weather Service study that analyzed 41 years of monthly climatological reports from Miami International Airport to understand better the seasonal shift in South Florida.
The study found the earliest end to summer — and beginning of autumn — was Sept. 24. The latest summertime end was Nov. 1. The median date was Oct. 17.
Brian McManus, a lieutenant with Palm Beach County Ocean Rescue and a 30-year veteran lifeguard, said he’s noticed a subtle change in the atmosphere with slightly drier air and sea breeze-cooled temperatures in the high-80s at the shore.
“We can tell out here, and we’ll take anything we can get because it’s so flipping hot,” McManus said. “It does seem like the fall pattern has gotten pushed back a little bit, and it’s staying warmer a little longer.”
That’s what Florida State University professor emeritus Morton Winsburg found at some official temperature measurement sites in Florida during a study co-authored with Melanie Simmons on the state’s “hot season.”
The study, an “Analysis of the beginning, end, length, and strength of Florida’s hot season,” found that the duration of Florida summers has grown longer in some urban areas, including West Palm Beach, which tacked on 23 days to its hot season between 1950 and 2007. Miami saw a whopping 45-day increase.
“For most Floridians, the end of the hot season is the most eagerly anticipated date,” Winsburg and Simmons noted in the analysis. “After a long and exhausting hot season, many Floridians long for the first few days when a cold front reaches them, lowering the temperature as well as the humidity to a more comfortable level.”
Molleda said weak cold fronts can push through the peninsula in October, but the stronger ones don’t make it down to South Florida until late October and early November.
But even North Florida isn’t expecting a big temperature dip in the near future with highs reaching into the upper 80s through at least next week.
“Fall is definitely around the corner, but it’s not here yet,” said Phil Peterson, a meteorologist with the NWS in Jacksonville. “It’s been a long hot summer.”
WHEN DOES FALL START?
Average dates of “fall arrival” in South Florida (based on average first date of temperature below 60 F):
LaBelle: Oct. 20
Belle Glade: Oct. 24
Moore Haven: Oct. 26
Naples: Oct. 29
Homestead/Redland: Oct. 30
West Palm Beach: Nov. 2
Fort Lauderdale: Nov. 4
Miami: Nov. 8
Miami Beach: Nov. 17
Source: National Weather Service
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