The heat took hold Friday, the clamp so humid two carriage ride companies voluntarily pulled their horses off the streets downtown. Saturday will be more of the same.

Upper 90s have been forecast for Saturday after downtown Charleston hit an official high of 96 degrees Friday. Humidity is expected to push the heat index, or real feel, as high as 107. A cooler weather front is expected to blow in Saturday night, and temperatures Sunday drop closer to 90, said meteorologist Doug Berry, National Weather Service, Charleston.

There's a chance showers and thunderstorms will accompany the cold front, he said. By Monday high temperatures should fall to the upper 80s.

Meanwhile, a storm system closing in on the Bahamas Friday was expected to turn into a tropical storm. Computer forecast models suggested the storm will turn out to sea and not threaten the Southeast coast, but forecasters cautioned the models are less reliable until a tropical cyclone actually forms.

"Significant uncertainty in the ultimate track and intensity remains," said the Weather Underground's Jeff Masters.

Temperatures on Friday pressed against triple digits throughout the Lowcountry. The official high at the weather service's Charleston International Airport station was 99 degrees.

Carriage horses and mules are taken off the Charleston streets when downtown thermometers record two 98 degree readings within 15 minutes. It came close enough that city Animal Control staff were down on Market Street by 3 p.m. actively watching the readings, and the swelter was so oppressive that Palmetto Carriage and Classic Carriage Works both pulled back their animals without waiting for the call.

People who attended an outdoor concert at Tanger Outlets from 6 to 7 p.m. Friday reported that children were passing out and throwing up because of the heat. Charleston County EMS stabilized one person having difficulties at the concert and took the person to a hospital for treatment, Director Don Lundy said.

Singer, actress and Disney star Bridgit Mendler was performing at part of the KidSTYLE fashion camp, which continues Saturday.

Four other people sought treatment at Medical University Hospital this week due to the heat, officials said. Two of those patients were children. Summerville Medical Center reported having one heat-related patient, a hospital official said. Calls to Trident Health System were not returned.

A smoldering mulch fire that started Thursday afternoon at Ladson Wood Recycling was finally extinguished about 5 p.m. Friday. Four firefighters were treated for heat-related injuries.

Dressed in long pants and sweat-stained T-shirts, crews crowded around a mist fan with bottles of water and Gatorade to seek relief from Friday's sweltering temperatures. The group took turns tending the mulch, allowing crew members to rest and rehydrate.

The mulch fire started when a piece of wood-chipping equipment went up in flames. Firefighters managed to contain the fire before it could reach a neighboring treeline, said North Charleston Fire Department spokeswoman Bianca Bourbeau.

Crews from St. John's, Charleston and James Island assisted in the effort.

When it comes to heat, the rules that firefighters live by are the same as those advised to the general public, Bourbeau said.

"We're hydrating often, taking frequent breaks, getting out of the sun and into the shade often," she said.

In Charleston on Friday, construction worker Hassan Robinson took a break from the heat and his day's work by grabbing an ice pop and a bottle of soda on Beaufain Street.

Nearby, a crew of workers hurried to refurbish a sidewalk as the beating sun hastened the rate at which the cement solidified.

"We take breaks every 15 to 20 minutes," said Earl Thorson, his head down, intent on smoothing the sidewalk's surface as sweat dripped from his nose.

Conley Bryan, an O'Dell Landscaping employee, said a drop in his workload helped ease the struggles of working in the day's heat.

His work Friday brought him to a shady stretch of Logan Street on peninsular Charleston.

"It's not so bad in the shade. Yesterday I was out in Mount Pleasant. There are a lot of sunny yards around there," he said. "It's hot, but you kind of get used to it after a while."

To safeguard against the heat, the National Weather Service suggested wearing light-weight clothing and staying indoors when possible, and warned not to leave children or pets in vehicles, especially with windows rolled up. Children and the elderly are most susceptible to heat-related illnesses.

Reach Bo Petersen at 937-5744, @bopete on twitter or Bo Petersen Reporting on Facebook.

Reach Christina Elmore at 937-5908 or at Twitter.com/celmorePC.