Inland Hillsborough under rare ‘excessive heat warning.’ Here’s what to know.

The National Weather Service on Wednesday issued an “excessive heat warning” for parts of west Central Florida, including portions of Hillsborough County — which might be a first for the Tampa Bay area, forecasters said.

An excessive heat warning is issued when the heat index could reach 113 degrees. Wednesday’s warning began at 11 a.m. and will run until 7 p.m., for Polk, Hardee, Highlands, DeSoto, inland Hillsborough, inland Manatee and inland Sarasota counties, along with other eastern parts of the state. The heat index could reach a staggering 115 degrees in those areas, the warning said.

Those not in an excessive heat warning are under a heat advisory in Florida, and heat indices there could reach 112 degrees.

The heat index refers to how the temperature feels to the human body when combined with the air temperature and humidity.

“Extreme heat and humidity will significantly increase the potential for heat related illnesses, particularly for those working or participating in outdoor activities,” the warning stated.

An excessive heat warning is rare, so much so that it may be the first ever issued for the Tampa Bay area, according to Nicole Carlisle, a meteorologist with the weather service’s Tampa Bay office.

Last year, the weather service issued an excessive heat warning for Levy County, Carlisle said, but there’s no record of one being issued for parts of Tampa Bay. Carlisle added a caveat: it is possible the records are incomplete or that the criteria for the warnings have changed over the decades.

The Tampa Bay office looks for heat indices to reach up 113 when issuing one of these warnings, but it’s up to the forecasters discretion to issue the warning, Carlisle said. How widespread the heat will be and how the day’s temperatures will shake out are factors in the decision, Carlisle said.

On Wednesday, the actual temperature will range from the mid-to-upper 90s across the area, with high humidity. Forecasters are not anticipating much rain, which could cool the area, leading forecasters to issue the warning, Carlisle said.

Forecasters warned those who work or spend time outside to take extra precautions on Wednesday, and to take frequent rest breaks in shaded or air-conditioned areas. The weather service suggests wearing loose-fitting, lightweight clothing when possible.

For information on heat-related illnesses and their symptoms, click here.