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It’s heat season. Expect more health warnings this summer in Miami-Dade

 Miami-Dade County Mayor Daniella Levine Cava speaks during a press conference outside of Government Center on Monday, May 15, 2023, in downtown Miami, Fla.
The Miami Herald
Miami-Dade County Mayor Daniella Levine Cava speaks during a press conference outside of Government Center on Monday, May 15, 2023, in downtown Miami.

The county will serve as a test case for the new heat warning levels. If they work well, the weather service may make them permanent and export them to other Florida counties.

At the urging of Miami-Dade County leaders, the National Weather Service has lowered the bar for extreme heat warnings and advisories in the county. The hope is that the new standards will better protect residents from the rising risks of heat, which the county estimates kills about 34 people and hospitalizes hundreds more each year.

NWS meteorologist Robert Molleda announced the change Monday at a county event marking the start of Miami-Dade County’s heat season, which officially runs from May 1 to Oct. 31 each year.

The decision has implications beyond Miami-Dade. The county will serve as a test case for the new warning levels, Molleda said. If they work well, the weather service may make them permanent and export them to other South Florida counties.

“The most important thing is that advisories and warnings go out when there is an increased threat to the general population,” said Molleda, the warning coordination meteorologist at the NWS Miami office. “It’s about making sure people have the information they need and are receiving weather alerts and notifications that can enable them to take action.”

Jane Gilbert, the county’s chief heat officer, said the change will help shape the response of emergency managers and public health agencies.

“We’ll be able to galvanize our emergency response resources when we get to those truly excessive heat temperatures and address the needs of our homeless population and those who can’t afford to keep their homes cool,” she said.

At the Monday heat season kickoff event, Miami-Dade County Mayor Daniela Levine Cava stressed that South Florida’s hottest days are becoming more common. The average number of days over 90 degrees has increased from 85 days a year in 1960 to 133 days a year, according to an extreme heat report the county released last year.

“In recent years, our summers are definitely getting hotter and longer due to climate change and to increasing urban development,” Levine Cava said. “We all feel it and it’s going to get worse. The heating will only increase.”

Lowering the threshold

Under the new system, the NWS will lower the threshold for heat warnings and advisories by 3 degrees. The weather service will now issue a heat advisory when the heat index reaches 105 degrees, and it will issue a heat warning when the heat index reaches 110 degrees.

The heat index is a measurement that combines temperature and humidity readings to give a sense of how hot it feels in the shade on a particular day.

That means that Miami-Dade residents can expect to see around five to 10 heat advisories a year, based on averages from recent years, according to Molleda.

County officials and local climate advocates have been urging the weather service to lower the heat warning threshold for more than a year. Last year, the county funded a heat vulnerability study that cataloged local heat deaths and the temperatures that caused them.

“Most heat related deaths are happening below [the old warning] thresholds,” Gilbert said.

The NWS decided to test out lower heat warning thresholds in Miami-Dade because of that advocacy, said Molleda, who sits on the county’s Climate and Heat Health Task Force along with Gilbert and a dozen other public officials, researchers and local advocates.

“The task force was a big driver behind this,” Molleda said. He also credited data shared from studies like the county’s heat vulnerability assessment with convincing the NWS to make the change.

Heat warnings save lives

When the NWS issues a heat advisory or warning, Miami-Dade residents may receive an alert on their smartphones — or see the announcement shared by local governments or news organizations on social media.

Meanwhile, the county will extend hours at parks facilities and libraries to give people an air conditioned place to cool off, according to Gilbert. The warning will also go to county officials at the Department of Emergency Management and the Homeless Trust to make sure they get the word out to vulnerable residents.

Weather service officials recommend drinking plenty of water and resting under the shade or inside an air conditioned room on extremely hot days to avoid heat stroke, heat exhaustion and other illnesses that can lead to hospitalization or death.

“The good news is, heat-related illnesses and death can be prevented,” Levine Cava said.

For Miami-Dade’s most vulnerable residents — people who work outside, can’t afford air conditioning or are pregnant, homeless or have a disability — a well-timed warning can be life-saving.

But county officials and the weather service are trying to strike a balance between sending out alerts every time heat becomes dangerous and making sure residents don’t get so many notifications that they start to tune them out.

“We need to be aware and careful every day,” Gilbert said. “But it would be too much of a resource constraint on the county and exhaust the messaging if we had lowered the threshold further.”

“We’ll test it and see,” she added. “We’ll have an actual chance to test our heat advisory and warning thresholds, which we haven’t had the opportunity to do. So we’re excited.”

This climate report is funded by Florida International University, the Knight Foundation and the David and Christina Martin Family Foundation in partnership with Journalism Funding Partners. The Miami Herald retains editorial control of all content.

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Nicolas Rivero