More than 55 million people are currently being warned of heat from Southern California through the San Joaquin Valley and in parts of the Northwest, including 20 of the most populous cities along the West Coast.
“Tempers can exceed 110F in parts of the Southwest where an excessive heat warning is currently in effect,” the Weather Prediction Center wrote.
The most foreboding areas will be in the Southwest, where the heat will be the most intense.
“Some records can be broken, but record max temps are very high at this time of year,” the NWS Los Angeles office said. “Record breaking or not, this prolonged heat wave is going to be very dangerous.”
In the West, more than 100 records could fall.
Prolonged heat wave for the Southwest
The kind of heat that will be felt from San Diego to Los Angeles to even Phoenix will be hard for even locals to tolerate.
“This heat could be record-breaking and will cause a very high risk of heat illness,” the NWS Los Angeles office said. “Three-digit heat is expected for many valley and mountain locations. Even warmer conditions are expected over the Labor Day weekend through early next week.”
The heat will begin on Tuesday, with a gradual warming through the week, and will peak towards the end of the week.
The reason for the extreme conditions is a persistent high pressure area overlying the region, creating what meteorologists call a “heat dome.”
This intense heat dome ensures that high pressure acts like a lid on the atmosphere. As hot air tries to escape, the lid forces it back down, heating it up even more as it sinks.
The result will be intense summer heat, with 10-15 degrees above normal.
“Excessive heat warnings are in effect for nearly the entire forecast area as of Wednesday and will continue through next Monday,” noted the NWS Los Angeles office.
The forecast shows temperatures of 110-115 degrees in the deserts and San Fernando Valley, with temperatures of 90-100 along the coast. That’s hot enough to potentially break records there too.
In Phoenix, the “dry heat” will give way to more humid weather on Thursday and Friday.
This will cause the actual temperature to drop slightly, but the NWS in Phoenix warns that the humidity can make it feel hotter.
In Southern California, a few morning clouds may roll in Friday morning, giving a brief reprieve from the heat — but it will be short-lived.
“There will be renewed warming leading to an oven-like day on Sunday,” the NWS Los Angeles office said.
Even downtown Los Angeles could hit 100 degrees on Sunday, with Death Valley potentially hitting 125.
This heat extends all the way into the San Joaquin Valley, where record-breaking temperatures are possible.
“Confidence is building that these are the highest temperatures yet this year,” said the NWS office in Hanford, California.
“Record high temperatures are possible from Thursday with the best chances of record highs on Sunday and Monday when the heat peak is expected.”
The Labor Day holiday will be one of the hottest days of the event, with heat potentially lasting for much of next week — making heat-related illness a major concern amid the oppressive heat.
Record heat for the Pacific Northwest
Maximum heat for inner parts of the Pacific Northwest will be felt for much of this week as high temperatures rise, including in Seattle, Portland and Boise.
“Daytime highs between 10-20F above normal and nighttime lows between 15-20F above normal are likely,” the Weather Prediction Center said.
The heat is expected to peak Wednesday with peaks in the 1990s and possibly reach triple digits for parts of the western basin, near Spokane, Washington – even breaking records.
“High temperatures are planned to be 10-15 degrees above average as several locations could test daily maximum temperature records,” the National Weather Service said in Seattle.
Near Boise, Idaho, temperatures could reach 20 degrees above normal, with record heat through Tuesday.
And in Seattle, the high temperatures are expected to top out in the upper 80s to 90s.
The extreme heat should break through by the end of the week, resulting in 70s temperatures for Labor Day weekend.
A Tropical Labor Day System Could Appear on the Horizon
The tropics are also warming up for the holiday weekend.
The National Hurricane Center is actively monitoring two areas in the Atlantic for tropical development, as we will most likely have our next tropical system before Labor Day.
A low pressure area a few hundred kilometers east of the Lesser Antilles has the greatest potential to become ‘Danielle’.
“While environmental conditions are only marginally favorable, gradual development of this system is expected in the coming days and a tropical depression is likely to form later this week,” the NHC said.
According to the NHC, there is an 80% chance that this area will become a tropical system within five days.
Forecast models take this system west, staying north of the Caribbean islands, and bending north, avoiding the Bahamas.
The storm should remain at sea as of now, but that could change between now and next week.
While the storm should stay out at sea, there will still be impacts on the East Coast over Labor Day weekend.
The storm could bring windy conditions and even strong rip currents off the east coast. How close the storm gets to the US will determine how strong the winds and rip currents will be. Closer to the coast they will be stronger, further from the coast they will be weaker.
The NHC is no longer tracking the western Caribbean area for development. However, that region still produces clouds and rain that will pump tropical moisture to the Texas coast. That will increase the chances of rain in South Texas over the Labor Day weekend.
Another area to watch is a tropical wave just off the coast of Africa. This area could also become a tropical depression in the coming days, although its lifespan may be short-lived.
“By the end of this week, the disturbance is expected to pass over cooler waters and further development is not expected,” the NHC said.
CNN meteorologist Judson Jones contributed to this article.