How Houston's Deluge Is Connected to L.A.'s Record Heat

Oppressive heat in Southern California will stick around for at least the rest of the work week, forecasters say. The record-breaking warmth is the backside of the same system that's helping to facilitate what one Texas official called  "800-year flood level" rain in Greater Houston, post–Hurricane Harvey, forecasters say.

"Basically we're under the influence of a high-pressure system that covers most of the western states," says National Weather Service (NWS) meteorologist Stuart Seto. "The influence on Tropical Storm Harvey is that it's not allowing it to push further inland. It's expected to move offshore, regain more strength and move back inland."

The high-pressure system over Nevada and Utah is putting up an atmospheric wall that extends into West Texas, holding incoming southern moisture in place, he explained. Over the weekend, UCLA climate scientist Daniel Swain predicted on his California Weather Blog that this is what would happen:

"Hurricane Harvey is already moving slowly but will continue to decelerate and eventually stall over land within 100 miles of the Gulf of Mexico over the weekend — potentially remaining within 150 miles of the Houston area for the next 5- to 6-plus days," he writes. "This extremely sluggish movement will occur due to the combined influence of the powerful Western ridge (which will prevent westward movement and rapid dissipation over relatively arid West Texas) and the lack of a deep trough over the central U.S. (which will prevent Harvey’s circulation from being 'picked up' by a larger passing storm). Thus, as the West Coast bakes amidst yet another prolonged heatwave, parts of the Gulf Coast may simultaneously experience an astonishing — and potentially devastating — tropical deluge."

While Houston is experiencing what some are describing as the worst flood-producing storm in U.S. history, Los Angeles will be dealing with much less dangerous but still serious weather, including a high temperature downtown expected to reach near 100 (about 97, to be precise) today, Seto says.

That represents peak heat for this wave so far, he says, but that doesn't mean it's not possible it will get hotter after a cool-down of 3 to 5 degrees next weekend, forecasters say. "The combination of strong high pressure and weak onshore flow will continue to produce dangerously hot temperatures across the region through at least the end of the week and possibly into the Labor Day weekend," according to an NWS "excessive heat warning."

Indeed, the Los Angeles County Department of Public Health has extended its "heat emergency" declaration through Friday.

"When temperatures are as high as they will be in the next few days, even a few hours of exertion may cause severe dehydration, heat cramps, heat exhaustion and heat stroke," the county's interim health chief, Jeffrey Gunzenhauser, said in a statement. "Others who are frail or have chronic health conditions may develop serious health problems leading to death if they are exposed to high temperatures over several days."

City Councilman Mitch O'Farrell reminded constituents that libraries, senior centers and other select parks buildings were doubling as cooling centers during the heat.

Records already started to fall Monday, according to the NWS. Palmdale and Lancaster tied their all-time highs for the date, both with readings of 107. Sandberg surpassed its record high for the date, 97 in 2008, with a reading of 103.

Seto said near-triple-digit highs would be the norm all week in the local valleys. Woodland Hills was looking at forecast highs of 110 today and 108 Wednesday, he said. Downtown will likely see highs in the mid-90s for most of the week, he said.

Lows downtown would be in the lower 70s; other inland areas, including valleys, would likely see lows in the mid-70s, Seto said. Slight offshore winds would keep ocean breezes at bay for much of the region, preserving warmer-than-normal readings, he said.

Swain of UCLA also wrote about the possibility that subtropical moisture and thundershowers could be drawn northward from Mexico, which isn't unusual for late summer.


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