(Bloomberg) -- The season’s first potent heat wave stretching from the Great Lakes to the Atlantic Ocean is set to raise electricity demand and slow transportation networks while threatening health risks.

Manhattan is set to reach 91F (33C) on Tuesday and steadily get hotter through the week with humidity making it feel closer to 100F, the National Weather Service said. Residents will find little relief at night because temperatures won’t fall that far, Allison Santorelli, a forecaster with the US Weather Prediction Center, said Sunday. 

“We’re looking at widespread record-breaking temperatures starting tomorrow across the Midwest into the Northeast and Mid-Atlantic,” Santorelli said. “This should last at least through this week and possibly into next weekend as well.” 

Electric grids and wholesale prices will be stressed as demand rises with the temperatures. Trains may have to run slower, tying up freight and passenger traffic, if tracks warp from getting too warm. Heat illnesses also may spike, with the elderly, children and outdoor workers particularly vulnerable. 

New Yorkers should prepare and remember heat is the top killer among extreme weather events, Governor Kathy Hochul said in a post on X. The coming “heat wave is no joke,” she said.

Chicago is forecast to reach 91F on Sunday and peak at 94F on Monday, the National Weather Service said. Washington will have highs above 93F throughout the week, with Boston, Cleveland, Philadelphia and Trenton, New Jersey, all among the cities wilting. 

Montreal is forecast to reach 95F Tuesday and Toronto may peak at 91F Thursday, according to Environment and Climate Change Canada. 

A large ridge of high pressure is trapping heat across the region and will let temperatures build throughout the week, Santorelli said. Excessive-heat watches have been posted across parts of Michigan, Ohio, Indiana, West Virginia and Pennsylvania and reach to Connecticut, Massachusetts and New Hampshire in the east.

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A severe thunderstorm watch is in place through late Sunday across the Midwest, including Chicago. These storms may bring high winds, downpours and hail.

(Updates with thunderstorms in final paragraph.)

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