All of South Florida under excessive heat warning, breaking even more records

All of South Florida was placed under an excessive heat warning Wednesday, breaking yet another record in 24 hours.

Wednesday was the first day that the National Weather Service Miami had to issue such a warning for its entire coverage area, which extends from Key Largo up to Lake Okeechobee. The warning expires at 7 p.m.

Tuesday had previously broken another record, with nearly all of the coverage under a warning, a first for Palm Beach, Glades and Hendry counties. Only mainland Monroe County was spared.

Wednesday is looking to be “almost a carbon copy” of Tuesday, said George Rizzuto, a meteorologist for the National Weather Service Miami. If anything, it will be a little bit hotter, he said, by one or two degrees.

Maximum heat indices, or "feels-like temperatures" could be as high as 116 degrees in some areas Wednesday. (National Weather Service)
Maximum heat indices, or “feels-like temperatures” could be as high as 116 degrees in some areas Wednesday. (National Weather Service)

By 9 a.m., temperatures were already in the upper 80s to lower 90s, the weather service said, with heat indices or “feels-like” temperatures between 100 and 110 degrees. Temperatures will continue to rise through the day, reaching the mid 90s along the coast and the upper 90s farther inland, with heat indices as high as 116 degrees in some areas.

To meet the criteria for an excessive heat warning in Broward and Palm Beach counties, the feels-like temperature has to reach at least 113 degrees for at least two hours, while in Miami-Dade, it has to exceed 110 degrees.

The stifling heat is due to a combination of high sea surface temperatures and low-level moisture largely brought by the Bermuda High, a “semi-permanent high pressure feature” over the Atlantic that has remained stationary for a prolonged period of time, Rizzuto said.

Nightfall has provided little relief. Temperatures didn’t even dip below 80 in most coastal areas Tuesday night.

“Really there hasn’t been much break at all from this heat,” Rizzuto said. “Usually you cool off overnight and ramp up again during day.”

The same pattern is in store for Thursday, he added, though possibly a “touch cooler.”

Coastal Broward may see heat indices between 105 and 110 degrees, while Palm Beach County may be even hotter, with heat indices between 110 and 115 degrees, similar to Wednesday.

Forecasters will issue updates on the heat later Wednesday afternoon.