Palm Beach County left out of new heat advisory triggers from National Weather Service

As South Florida staggers into another molten hot summer, the National Weather Service has lowered the temperature thresholds on heat alerts in Palm Beach County’s two southern neighbors but maintained current rates for the northern reaches of the Gold Coast.

The reduced temperature triggers on heat advisories and excessive heat warnings were announced Thursday and went into effect for Broward County this summer to match what was put in place in Miami-Dade County last summer.

It means heat advisories will be issued in Broward and Miami-Dade when a heat index, or “feels like” temperature, of 105 or higher is expected for at least two hours. An excessive heat warning will be issued if the heat index is expected to reach 110 or higher for at least two hours.

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In Palm Beach County, and the five other counties overseen by the NWS Miami office, including Collier County, the thresholds will remain 108 or higher for at least two hours for a heat advisory and 113 or higher for at least two hours for an excessive heat warning.

Robert Molleda, meteorologist in charge at the NWS Miami office, said the changes were made at the request of the counties and align better with “local climatology” as well as recent health data that shows people get sick from temperatures lower than the current thresholds.

He said Palm Beach County may be included in the lower thresholds if it requests it and after an assessment this summer of how the alerts are issued in Broward and Miami-Dade.

“The bottom line in all of this is every part of our forecast area will still get alerted at the appropriate times,” Molleda said. “The changes aren’t permanent yet. We want to see how it’s applied, and last year was a good start to evaluate it.”

Why did Broward County request the lower threshold?

Molleda said the changes in Broward and Miami-Dade are based on current health data, not necessarily climate change. He said the thresholds can be readjusted if rising temperatures or longer bouts of extreme heat warrant it.

Jennifer Jurado, deputy environmental director and chief resilience officer for Broward County, said county commissioners approved a resolution in October requesting the threshold change after several presentations on extreme heat.

"The lower threshold will help ensure we maintain a proactive approach, especially under conditions of rising temperatures with climate change, and the risk this generates," Jurado said.

The change comes as the country is grappling with a heat wave

The change for Broward County comes as summer is heating up across the country and the National Weather Service is considering an experimental heat risk index that it hopes will better translate health complications that occur at temperatures rise.

On Friday, about 8 million people nationwide were under an excessive heat warning — the highest concern level — as a stubborn area of high pressure remained parked over areas from Michigan and Indiana to southern New England.

An additional 74 million people nationwide were under a heat advisory, the tier below an excessive watch or warning.

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“It’s a little early for some of these areas to see these temperatures, but it’s not unprecedented,” said Marc Chenard, a meteorologist with the Weather Prediction Center. “We’ve had heat waves lasting this long before.”

Generally, a heat advisory is issued when the heat index temperature is expected to be 100 or higher for at least two days and overnight temperatures won’t drop below 75.

That’s obviously different for South Florida, where people are more accustomed to warm, muggy conditions. But that higher tolerance was tested last summer when a flamethrower of western winds and record warm sea-surface temperatures led to prolonged periods of very high heat index values “rarely if ever observed on record in South Florida,” the NWS said.

Palm Beach County Mayor Maria Sachs said she supports considering a temperature threshold change for heat alerts to align with Broward and Miami-Dade counties and will bring it up with the board of county commissioners.

"It's not just hurricanes that we deal with. It's also extreme heat and the impacts of climate change," she said. "We're going to face it again this summer."

Last summer, West Palm Beach had heat index values of 105 degrees or greater for more than 130 hours. That broke the previous record of 50 in 2011.

Heat index values of 110 degrees or greater were measured in West Palm Beach for 10 hours, surpassing the previous record of four hours in 2009.

What exactly is the heat index temperature?

The heat index temperature is calculated through an equation that considers ambient temperature and the amount of moisture in the air, using the dew point or relative humidity. Dew point is the amount of water vapor in the air. Relative humidity is a percentage describing the amount of saturation of air.

A higher dew point makes the body's natural cooling mechanism — sweat — less efficient.

There were 39 days under a heat advisory in Palm Beach County and three excessive heat warnings. Both alerts are based on heat index temperatures, and both set records.

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Molleda said in his 2023 year-end weather summary that the summer heat contributed to a death in Homestead in July, and the hospitalization of 26 people at an outdoor festival in Lauderhill in October.

Miami-Dade County advocated for the heat thresholds to be lowered because data showed that severe health impacts were occurring at lower temperatures and that all people are at risk of heat-related illnesses when exposed to heat indices of 105 or more, said Miami-Dade County Resilience Coordinator Sandra St. Hilaire in an email.

She said it is hard to gauge how the lower thresholds affected Miami-Dade last summer but that they did increase public awareness.

"While we did have an increase in heat-related emergency department visits, the increases were not as dramatic as they could have been," said Hilaire, who noted that Miami-Dade has a list of public libraries and parks that it considers cooling centers on its website.

Already this year, a heat advisory was issued for Palm Beach County in May — the first for that month in at least two decades.

"We don't deal much with heat-related health concerns presently, but I anticipate that these concerns will likely increase, unfortunately," said Patrick McNamara, president and CEO of the Palm Health Foundation in West Palm Beach.

The Climate Prediction Center says there’s up to a 70% chance that temperatures in all of Florida will be above normal through September.

Molleda said counties can contact the National Weather Service if they are interested in changing the thresholds for their heat alerts.

“Any county will have to have internal discussions if they want to be part of it. Then we can take that into consideration,” Molleda said. “These decisions are based, at least from the National Weather Service’s perspective, on making sure we are meeting the current needs of our populations.”

Kimberly Miller is a journalist for The Palm Beach Post, part of the USA Today Network of Florida. She covers real estate and how growth affects South Florida's environment. Subscribe to The Dirt for a weekly real estate roundup. If you have news tips, please send them to kmiller@pbpost.com. Help support our local journalism: Subscribe today.

This article originally appeared on Palm Beach Post: Heat advisories changed for Broward, Miami-Dade but not Palm Beach