It’s hot enough for a heat advisory in Collier County, but step across the county line into Lee and you’ll be cooler. Right?
Not exactly.
While the heat advisory in Naples, Immokalee and other points in Collier and eastward has been in effect for the past week, Lee, Charlotte, and Sarasota have been relatively advisory-free. But, it’s still been hot. Actually, close to advisory hot.
So, what’s the difference?
The big difference is sustainability of the heat index plus humidity levels.
For today, the National Weather Service continued a daily heat advisory until 8 p.m. for parts of southeast, southern and southwest Florida –- coastal and inland Collier County, as well as Hendry and Glades counties and other points east. The advisory is also to be in effect until 8 p.m. on Saturday and Sunday.
But, further north, into Lee, Charlotteand Sarasotacounties, heat index values could reach from 102 to 106 today and into Saturday. However, no heat advisory has been issued for this area.
The reason for that, a National Weather Service forecaster in Tampa said, is that the area from Naples to West Palm to Miami is under the Miami National Weather Service office, while the Fort Myers to Sarasota area is covered by the Tampa Bay Area NWS office. The criteria for calling a heat advisory is different for each office, the NWS forecaster said.
The Tampa office is working under current advisory criteria requiring heat indices over 108 remain at that level for two hours for an advisory to be called. That has not yet occurred along the western coast from Fort Myers northward, the NWS forecaster said.
Additionally, the Tampa forecaster said moisture levels were slightly different in the Fort Myers to Sarasota area.
Will Redman, a forecaster at the Miami office, said that an experimental advisory criteria was recently put into place there.
"It was changed this year; it's experimental," Redman said. That office’s new temperature level for calling a heat advisory was lowered to 105. He added that the new criteria only affected the Miami-Dade area.
Redman said that the Naples area and inland Collier and other areas outside Miami-Dade remained under the former 108-degree criteria and that two-hour mark has been met there.
So, while it might feel just as hot in Lee County as it does a quarter-mile down U.S. 41 into Collier, the heat advisory situation is slighty different.
The weather service also said that while heat index values will fall below advisory criteria during the night hours, heat indices in the 90s will be common during each overnight period into the upcoming weekend.
The continuing higher heat index numbers should extend into the weekend, the NWS forecasted. A little extra moisture will lift over the area from a tropical wave, then merge with the moisture from the stalled frontal boundary and allow for the chance of rain rising from 40 to 60 percent into the weekend and early next week.
The heat index, also known as the apparent temperature, is what the temperature feels like to the human body when relative humidity is combined with the air temperature. There is direct relationship between the air temperature and relative humidity and the heat index, meaning as the air temperature and relative humidity increase (decrease), the heat index increases (decreases).
Scattered to numerous showers and thunderstorms will develop across portions of South Florida this afternoon and evening. Biggest hazards with these will be heavy downpours, gusty winds and frequent lightning. A few winds gusts in excess of 50 mph will be possible with stronger storms especially over the interior areas.
Heat index values will remain high into the upcoming weekend, ranging between 105 and 110 each afternoon and early evening with some localized areas having heat indices exceed 110 degrees.
Areas impacted include Gladesand Hendrycounties,coastal and inland Collier County and most points directly east and south, including the cities of Muse, Ortona, Palmdale, Lakeport, Moore Haven, Brighton Seminole, Buckhead Ridge, Felda, Hendry Correctional, Clewiston, Lion Country Safari Park, Wellington, Belle Glade, East Naples, Naples, Marco Island, Marco Island Airport, Royal Palm Hammock, North Naples, Golden Gate, Orange Tree, Bunker Hill, Immokalee, Miles City, Sunniland, and the Miccosukee Indian Reservation.
In the west coastal and inland areas of Lee, Charlotteand Sarasotacounties, some tropical moisture will move over the area Saturday, then moisture from a stalled front will move in Sunday and linger into early next week. This will allow for scattered to numerous showers and storms through the period, with the best chances continuing to be inland with the westerly flow dominating.
Highs will also continue in the lower to mid 90s, with some isolated pockets of upper 90s possible. Afternoon heat indices will also top out around 105. Lows remain in the mid 70s to around 80 near the coast.
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