During a heat wave the body has to work harder to maintain a normal body temperature. Here are five facts to keep in mind when dealing with intense heat. (Claritza Jimenez/The Washington Post)

The most stifling weather of the year is expected to start moving into the Washington region Friday, building through the weekend with temperatures nearing 100, and peaking early next week with heat indexes even higher.

Forecasters are calling for readings to soar into the upper 90s, and beyond, through late next week, flirting with records and posting temperatures 10 degrees above the average highs in the upper 80s.

The record high for Friday’s date at Reagan National Airport is 103, set in 1926. It doesn’t appear likely that temperatures there will break the record Friday or either of the next two days. The record for Saturday is 102, set in 2011, and for Sunday is 101, set in 2010.

But one weather model has Monday’s high around Washington at 104. The record high for that date in Washington is 100, set in 1930.

“The National Weather Service issues heat advisories when the heat index has the potential to reach 105 degrees,” Jason Samenow, chief meteorologist with The Washington Post’s Capital Weather Gang wrote Thursday.

“And we expect such advisories will be issued on most if not all of the days between Friday and Monday,” he wrote.

“On multiple occasions, we may match or best the summer’s highest temperature registered so far of 98 degrees” on July 14, he wrote. “And for the first time this summer, we should string together consecutive days above 95 degrees.”

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The mercury around Washington has not reached 100 since July 26, 2012.

Hot weather was expected to overspread much of the country by Monday, from the Midwest to New England.

Local officials warned people to take precautions, and said they were taking emergency measures.

“Stay safe as it heats up,” President Obama tweeted Wednesday. “Drink water, stay out of the sun, and check on your neighbors.”

The D.C. Fire and Emergency Medical Services Department said it will add five ambulances to its fleet to help with calls that officials says they anticipate will increase over the weekend.

On a typical day, the department has 25 basic life support ambulances and 14 advanced life support vehicles staffed by paramedics who can administer IVs and drugs. In addition, there are 25 private ambulances helping the city run routine calls from 7 a.m. to 1 a.m.

Fire officials are adding five more transport vehicles — a mix of basic and advanced life support from Friday morning through 11 p.m. Monday, said Doug Buchanan, the fire department’s chief spokesman.

“Our up-staffing is directly related to the extreme weather we are anticipating,” Buchanan said.



Water drips off Hermon Getu after he poured water over his head following a soccer game earlier this month in Washington. Some of the hottest weather of the summer is in the region through the weekend. (Matt McClain/For The Washington Post)

Buchanan also said that officials will do all they can to persuade people not to open fire hydrants to get water to stay cool. The practice is illegal and depletes water needed to fight fires.

D.C. Police Chief Cathy L. Lanier said officers in neighborhoods, particularly officers on walking tours, will check in on elderly people living in their patrol areas. She said supervisors will be out to ensure officers have enough water.

The District opened a hyperthermia hotline at 800-535-7252 for people in dire need of relief. And the city urged people to cool off at cooling centers, public swimming pools and “spray parks.”

[Here’s a map of Washington’s cooling centers, spray parks and swimming pools]

Officials in the surrounding counties also are issuing advisories and setting up cooling centers. In Fairfax County, cooling centers have been set up in libraries and community centers. Montgomery County is telling residents without air conditioning who are unable to get to a cool place to call the crisis center at 240-777-4000.

“Humidity throughout the heat wave will be moderate to high but probably not off-the-charts,” Samenow reported. “Still, moderate to high humidity will frequently make air temperatures feel at least 5-10 degrees hotter than they actually are.

“Saturday and Monday are likely to be the most humid days,” he wrote. “Humidity may ease slightly on Sunday.”

Of dubious comfort may be the outlook for Phoenix, where it was 110 Thursday, with forecast highs of 113 Friday and Saturday.

Or, as Andy Woodcock, a lead forecaster at the Weather Service, points out: Exactly six months ago — Jan. 22 through 24 — Washington was getting buried under 30 inches of snow.

[Remember the blizzard? Cool off with these images.]