Temperatures will top 90 and the heat index will feel about 100 degrees.

Chicago could be in for the hottest day of the summer Tuesday, with temperatures in the 90s to go with higher humidity.

The National Weather Service is predicting heat indexes – which combine temperature and humidity into one uncomfortable number -- in the 95-to-100-degree range.

It could be only the third 90-degree day of what’s been an unsuually cool summer in Chicago. That contrasts with a yearly average in recent decades of 14 such days, said Jamie Enderlen, a meteorologist with the National Weather Service.

"Right now we're below, well below the usual," she said. "But we still have plenty of summer left."

The average temperature for July so far has been 78.7 degrees, which is five degrees lower than the average monthly temperature of 84.1 degrees. The average monthly temperature for August is usually lower than July, at 81.9 degrees, Enderlen said.

The weather service’s one-month outlook for August temperatures is also below normal, as is the three-month forecast for August, September and October, she said.

The steamy combination of heat and humidity on Tuesday also sets the table for afternoon thunderstorms, some of which could become severe, the weather service said. High winds, hail and locally heavy rain are all possible from the storms, which are expected about 4 p.m. in parts of northeast Illinois.

The Weather Service’s Storm Prediction Center says the Chicago-area is at slight risk for severe thunderstorms today and tonight.

WGN-TV meteorologist Tom Skilling says temperatures will drop back down into the high 70s on Wednesday and Thursday before moving back into the 80s on the weekend. Rain is back in the forecast for Saturday.

Tribune reporter Marwa Eltagouri contributed.

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