Further to the northwest, however, thermometers will have a hard time, as thunderstorms and torrential rain may develop.

The rising temperatures show no signs of slowing in the fall, even reaching New England and New York.

Jim Dale, US meteorologist for British Weather Services, said: “The heat is developing into heatwave conditions in the east of the country, coming from the Gulf of Mexico.

“It’s colder in the west and in the north, but there’s a chance this heat will spread to the western states.

“The storm may miss the far north of the region and not reach as far as Washington and surrounding areas.”

He warned that atmospheric instability will create violent storms where warm and cold air masses meet.

“The risk of storms is still there,” he said.

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“Where warm and cold air meet, there will always be instability, and that will bring torrential rain, thunderstorms and the threat of tornadoes.

“However, in parts of the country we are seeing temperatures above 30 degrees Celsius, which is unusual for this late in the season, thanks to this plume coming from the south.”

The US National Weather Service (NOAA) has issued high wind and flood warnings in Kansas, Wyoming, North Dakota and Montana.

Isolated storms are moving in off the Pacific coast, putting the northwestern states on alert for thunderstorms, the agency warned.

A spokesman said: “Another system approaching the Pacific Coast will bring some scattered showers and storms to the Pacific Northwest coast, spreading southward into Northern California and the central Great Basin.

“In terms of temperatures, much of the northern central and eastern US, as well as the Plains, will remain well above average.

“Highs will reach between 80 and 95 degrees Fahrenheit across parts of northern New England and the Upper Midwest on Wednesday, and a handful of near-record highs near 100 degrees Fahrenheit will be possible across parts of the southern Plains on Thursday.”