PHOENIX — More than 75 million people in the United States were under extreme heat alerts on Monday as a heat wave moved eastward, and the mid-Atlantic and New England were likely to see highs reaching 37 C as the week progresses. Excessive humidity will make it feel even more oppressive and officials warned residents to take precautions.

The US last year saw the most-ever heat waves, consisting of abnormally hot weather lasting more than two days, since 1936.

Much of the Midwest and Northeast were under heat warnings or watches.

The heat has been especially dangerous in recent years in Phoenix, where 645 people died from heat-related causes last year, which was a record. Temperatures there hit 44.4 C on Saturday. Weather service forecasters said the first two weeks of June in Phoenix have been the hottest start to the month on record there.

Ted Whittock, a meteorologist with the National Weather Service in Phoenix, advised reducing time outdoors between 10 am and 6 pm, staying hydrated and wearing light, looser fitting clothing. More than 100 cooling centers were open in the city and surrounding county, including two new overnight ones.

In neighboring New Mexico, the high in Roswell was expected to hit 41.7 C on Monday, while temperatures in southern Colorado were expected to surpass 37.8 C.

Containing wildfire

In Southern California, firefighters increased their containment of a large wildfire in mountains north of Los Angeles on Monday after a weekend of explosive, wind-driven growth along Interstate 5.

The warming temperatures come amid growing concern about the effects of extreme heat and wildfire smoke. The nonprofit Center for Biological Diversity sent a petition on Monday to the Federal Emergency Management Agency, or FEMA, asking it to recognize extreme heat and wildfire smoke as major disasters.

The agency did not immediately issue a specific response to the petition. A FEMA spokesperson for the western US states said there was nothing that would preclude an emergency declaration for extreme heat, but noted that there would need to be an immediate threat to life and safety that local authorities could not respond to.

While much of the US swelters, late-season snow was forecast for the northern Rockies on Monday and Tuesday.

Parts of Montana and north-central Idaho were under a winter storm warning. As much as 51 centimeters was predicted for higher elevations around Glacier National Park.

Meanwhile, a fresh batch of tropical moisture was bringing an increasing threat of heavy rain and flash flooding to the central Gulf Coast.

Hurricane season this year is forecast to be among the most active in recent memory.

Agencies via Xinhua