September is keeping summer going strong with heat warnings expected to cover 26 million people, mostly in the Southwest, by Wednesday.
Temperatures in cities such as Los Angeles, Las Vegas and Phoenix could be 10 to 20 degrees above normal starting Tuesday and peaking Thursday, according to federal and NBC News forecasters.
A mass of warm air pushing down on the Earth’s surface, known as an upper-level ridge, is strengthening over the Southwest and blocking cool air from the Pacific Ocean, setting up conditions for dangerous heat from California’s Central Valley east of San Francisco to the U.S.-Mexico border at Arizona.
“Above average temperatures are forecast to span much of the West Coast, including the potential for a few daily records,” the National Weather Service said Sunday in a special message about the heat wave.
The weather service office for Los Angeles said Monday that high temperatures of 98 to 113 degrees are possible starting Wednesday, with the hottest communities likely to be in the western San Fernando Valley.
Los Angeles Mayor Karen Bass said Monday she’s deploying city resources, including “augmented cooling centers” and emergency operations personnel, to prepare. The extra cooling centers will open Tuesday morning, her office said in a statement.
Public libraries, parks facilities, recreation centers, senior centers, community pools and splash pads, and hydration stations and shade structures will be made available, her office said. A dedicated cooling center, ReFresh Spot, with access to drinking water and showers, is open 24 hours in Skid Row, it said.
An excessive heat warning was expected Wednesday through Friday for most of Southern California’s most-populous counties: San Diego, Orange, Los Angeles, Ventura and Santa Barbara, as well as for the Inland Empire of desert and mountain communities that extends nearly to Las Vegas.
The warnings start at the U.S.-Mexico border and extend up the coast to the ragged coastline near San Simeon, California, federal forecasters said. They extend eastward into Arizona and cover Southern Nevada.The National Weather Service office for Las Vegas, where this summer was declared the hottest in recorded history, scheduled a lower-level excessive heat watch for the same time. It called for temperatures as high as 108 midweek.
“Drink plenty of fluids, stay in an air-conditioned room, stay out of the sun, and check up on relatives and neighbors,” the weather service office said in an urgent weather message about the heat wave.
The office covering Phoenix similarly issued a heat watch for the latter three days of the week, saying in its urgent weather message Monday that “dangerously hot conditions [are] possible.”
An excessive heat warning describes impending heat that is a certainty and is a “significant” threat to life, according to the National Weather Service. A watch is issued when such heat is likely but there’s a day or two to prepare, the weather service said.
The East Coast, meanwhile, was expected to continue experiencing normal to below-normal temperatures, while the Gulf Coast of Texas could welcome thunderstorms.
Heat in the West was not likely to help dry, windy conditions in northern Plains states, which include Iowa, Nebraska, North Dakota, South Dakota, Kansas and Oklahoma. The region was covered by a federal “critical fire weather” forecast for the workweek.
Christine Rapp contributed.