DETROIT, United States (AP) — The heatwave that has been roasting much of the US in recent days is just getting warmed up, with temperatures expected to soar to dangerous levels through the weekend.

Communities are preparing by offering buildings as cooling centres and asking residents to check in on relatives and neighbours. Officials also are concerned about smog, which is exacerbated by the heat and makes it more difficult for certain people to breathe, including the very young, the elderly, and people with asthma or lung diseases.

More than 100 local heat records are expected to fall Saturday, according to the National Weather Service. Most won’t be record-daily highs but record-high night-time lows, and that lack of cooling can be dangerous, meteorologists say. Temperatures in parts of the east won’t drop below the mid- to upper-70s or even 80 ° Farenheit (26.7° Celsius) at night, he said.

The heatwave will likely be “short and searing”, said Greg Carbin, forecast branch chief for the weather service’s Weather Prediction Center.

A high-pressure system stretching from coast to coast is keeping the heat turned on. The heat and humidity are worsened by the large amount of moisture in the air coming from the Gulf of Mexico, much of it left over from Hurricane Barry.

The heat index, which is what the temperature feels like, should hit 110° Farenheit (43.3° Celsius) in Washington, DC, on Saturday and was expected to hit 109° Farenheit (42.8° Celsius) in Chicago and Detroit yesterday, said Jeff Masters, meteorology director of Weather Underground. Wednesday marked Washington’s seventh-straight day with temperatures of at least 90° Farenheit (32.2° Celsius), and that streak was expected to last for another five days.

An experimental weather service forecast projects that today, 101 records could fall in an area stretching from Texas to Iowa and east to Maine and Florida.