Excessive heat and some severe storms expected Saturday, first May heat advisory for Broward in 15 years

Excessive heat and some severe storms are expected Saturday — with the forecast calling for “feels-like” temperatures as high as 110 degrees throughout South Florida, the National Weather Service says.

The National Weather Service’s Miami office issued a heat advisory on Friday for Miami-Dade — marking the first heat advisory in May in the past 15 years or more. Another heat advisory was issued Saturday for the entire South Florida region, including both Broward and Palm Beach Counties, which marks the first May heat advisories for those areas as well.

“This is definitely abnormal for May,” said Chris Fisher, a weather service meteorologist. “We’re seeing heat indices that we typically would see in July and August. It’s certainly abnormal. We may get some relief from scattered showers, but regardless of that, it’s going to be very warm and very humid.”

Heat indices are calculated by combining air temperature and relative humidity.

Miami-Dade, Palm Beach and Broward counties are all under a “significant excessive heat risk” warning Saturday, meaning a heat index of 108-112 degrees, where dangerous and potentially deadly heat stroke is likely with prolonged exposure.

“Anyone sensitive to heat should plan to avoid extended time outside, and if you are required to be outside, take cooling breaks and stay hydrated,” meteorologists wrote in the local weather forecast Saturday morning.

Palm Beach County will feel the brunt of the heat because it is under the northern edge of a southwest wind flow pattern that is driving the heat, Will Redman, a weather service meteorologist, said Saturday.

Saturday is likely to be the hottest day of the heat wave, forecasters say. Excessive heat risk Sunday will dwindle slightly to “elevated,” meaning maximum heat indices in the 103-107 range. By Monday, those temperatures will lower again to a “limited” risk at 98-102 degrees.

A normal overnight low temperature for May 18 is 74 degrees, according to weather service records, but lows Friday night remained around 80 degrees, giving Saturday’s heat a head start. Temperatures will likely remain in the 80s Saturday night in most places, Redman said.

A normal maximum temperature in Fort Lauderdale for May 18 is 86 degrees F, but temperatures will reach the mid to upper-90s Saturday — hotter than normal maximum temperatures in August (90 degrees).

If the excessive heat isn’t enough to keep people inside, some severe weather is also in store for South Florida Saturday. Eastern cities like Fort Lauderdale and Boca Raton are at a “marginal risk” for storms between 2 and 8 p.m., forecasters say. That threat will spread to the rest of the region on Sunday.

Sunday will be slightly less hot, with the region experiencing “elevated” heat risk, with potential heat indices of 103 to 107 degrees.

Some mild relief is in store going into next week. Temperatures are expected to decrease gradually each day after Sunday with highs hitting the mid-80s on Wednesday, before increasing again by next weekend.

What’s contributing to the hotter temperatures?

“It’s mainly because we’ve had a prolonged southerly flow (of wind). Anytime we have a south or southwest flow, it’s typically when we get our hottest temperatures here in South Florida,” Fisher said. “Unlike an easterly flow, where wind is coming directly off the water, if you get a south or southwest flow, the air is across a land mass and giving it time to heat up as it’s going across the peninsula.”