Weather alert: Miami-Dade issues heat advisory for a ‘feels like’ of 108. What it means

South Florida is under a heat advisory from noon until 7 p.m. Friday, the first time the National Weather Service in Miami is using a new lower threshold that forecasters and Miami-Dade officials approved in May.

Wednesday’s high will be near 90 degrees — but the heat index is expected to reach 105 to 108 degrees.

The weather service extended the initial advisory from Wednesday evening out to Friday given the stretch of hot days ahead.

“The combination of lower rain chances and ample humidity will once again result in apparent temperatures — heat indices — reaching the heat advisory criteria each afternoon through Friday,” the service said early Wednesday afternoon.

What counties are in the alert area?

If you live in Southeast Florida and portions of Southwest Florida, such as Miami-Dade, Broward, Palm Beach counties, and Fort Myers, Immokalee, Naples, Everglades City and Arcadia, you’re in the advisory zone where the heat index will be at least 105 and could go up to 108.

The at-least 105 “feels-like” locales include Miami, Homestead, Hialeah, Kendall, Carol City, Hollywood, Fort Lauderdale, Pembroke Pines, Coral Springs, Sunrise, Davie, Miramar, Pompano Beach, Deerfield Beach, West Palm Beach, Boca Raton, Jupiter and Riviera Beach.

The closer to the coastline you get, like Miami Beach, the slightly cooler it will be from breezes off the water compared to inland cities.

Orlando expects a high of 95 on Wednesday and Thursday and will remain hot through the week. As of Wednesday, the expected heat index is 102 to 107, which is under the threshold to trigger a heat advisory in Central Florida. The index has to hit and sustain 108.

What is the heat index?

The heat index is a measure of how hot it really feels when relative humidity is factored in with the actual air temperature, according to the weather service. This is how hot it “feels like” on your skin on steamy days.

The weather service will initiate alert procedures when the heat index is expected to exceed 105 to 110 degrees depending on local climate for at least two consecutive days.

The new standards

Earlier in June, Miami-Dade County Mayor Daniella Levine Cava and weather service officials announced plans for raising awareness of environmental extreme heat hazards and presented changes in county and weather service protocols.

Among the initiatives: the declaration of a Miami heat season that runs from May 1 to Oct. 31. Miami-Dade will serve as a test case for new warning levels that trigger a heat advisory.

Previously, the weather service issued a heat advisory when the heat index hit 108 degrees. Now, the local weather service in Miami will issue a heat advisory if the index is 105 degrees for at least a couple of hours, Miami weather service meteorologist Chris Fisher told the Miami Herald before the strategy got its first test with Wednesday’s alert.

The goal is to spread awareness so that people protect themselves from extreme heat that leads to about 34 deaths and hundreds of hospitalizations every year, according to county estimates.

Tips to prevent heat exhaustion and heat stroke

Miami-Dade County issued several hot weather survival tips, based on U.S. Centers for Disease Control and Prevention advice, and noted who is most at risk in recent postings.

Who is most at risk of heat-related illnesses: Older adults 65 and older, young children, people with chronic health conditions or mental illness, athletes who exercise outdoors, outdoor workers, people living unsheltered or with limited access to air conditioning, pregnant people, and pets.

What you should do:

▪ Stay cool by spending time in air-conditioned buildings.

▪ Avoid direct contact with the sun.

▪ Reduce physical activity and move to shaded areas.

▪ Do outdoor activities in the cooler morning or evening hours, and dampening your shirt or wrapping a wet scarf or bandana around your neck or forehead could also help.

▪ Stay hydrated and drink plenty of water or drinks with electrolytes if you’re sweating. Don’t wait until you’re thirsty to drink more. Use sunscreen, too, to protect against skin damage.

▪ Limit or avoid dehydrating caffeine and alcohol.

▪ Never leave infants, children or pets in a parked car, even if the windows are cracked open.

▪ Watch for signs of heat exhaustion or heat stroke. Seek medical care immediately if you know someone who experiences symptoms that could include high body temperature, headache, dizziness or nausea and confusion.

What about thunderstorms?

Afternoon and evening thunderstorms are still in the South Florida forecast, at 20% Wednesday and increasing as the weekend approaches. Saturday and Sunday chances are 60%.

Key West’s low of 84 degrees Tuesday set the daily warm minimum temperature record, breaking the previous record of 83 set in 2001. Wednesday morning’s low was also 84° and if it stands will tie this date’s warm minimum record, the weather service said.

Highs are expected in the low 90s in the Keys.

Rain chances in the Keys are 10% and rise to 30% by Saturday night.