File photo. (Pixabay)

Thursday will be the longest day of the year, which means Chicago area residents have even more time to enjoy the day’s hot and humid conditions.

Astronomical summer officially begins at 3:50 p.m. on Thursday, when the sun shines directly on the Tropic of Cancer, according to the National Weather Association. Thursday will see nearly 15 hours and 14 minutes of daylight.

Isolated storms are possible along the I-80 corridor in the afternoon and evening, according to NWS forecasts. Downpours, gusty winds and lightning strikes are possible in some areas, mainly to the west of the city.

As far as the heat goes, temperatures have dipped from the record-highs experienced earlier this week with Thursday expected to reach 87 degrees.

That temporary relief may be short lived.

Sweltering temperatures will return in the next few days, with Friday’s forecasted high at 90 degrees and a toasty 96 degrees predicted for Saturday.

The Chicago area is not alone when it comes to warm weather.

Heat index readings combining temperature and humidity were expected to surpass 100 degrees across the Great Lakes and New England on Thursday and into the Ohio Valley and Mid-Atlantic over the weekend.

Last year, the U.S. saw the greatest number of heat waves — abnormally hot weather lasting more than two days — since 1936.

This year, ocean waters are warmer, particularly in the Gulf of Mexico. It’s made for an unusually early start to extreme high temperatures.

Chicago set a record-high on Monday when the mercury hit 97 degrees at O’Hare Airport.

The city has multiple cooling centers open, and people can also escape the heat at public libraries and Park District fieldhouses. 

Cooling centers are open from 9 a.m. to 5 p.m. at the following locations:

— Englewood Center, 1140 W. 79th St.
— Garfield Center, 10 S. Kedzie Ave.
— King Center, 4314 S. Cottage Grove
— North Area, 845 W. Wilson Ave.
— South Chicago, 8650 S. Commercial Ave.
— Trina Davila, 4312 W. North Ave.

The Associated Press contributed.