As National Weather Service forecasters gauged a heat wave that has moved across the Bay Area, they initially thought the high-pressure system would be strong enough to keep the temperatures excessively high for a couple days. Then they gauged it would do so for a third.
Now, a fourth day of temperatures that will exceed 100 degrees in the hottest areas and threaten it in others is likely on tap, according to forecasters.
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“Remember how we had that wide high pressure in July that was so strong that it was hard to move?” NWS meteorologist Brayden Murdock said Friday morning of a month that hit triple digits a dozen times. “Well, this one is not quite that. But it has been stronger than we thought it would be, and it’s progressively slowed down. So that’s why the heat has maintained this week as long as it has.”
Temperatures that were expected to be 3-4 degrees cooler on Friday instead now are expected to be just as high as they were the previous two days. The hottest spots in the region are expected to top out at about 101 degrees, according to the weather service, and a heat advisory remained in effect for most of the region until 8 p.m. Friday.
This time, the heat is coming with an added element.
“It’s gonna be muggy,” Murdock said. “We’ve got a little bit of moisture coming up from the south, and the other big part of it is that the marine layer is very compressed and is containing a lot of moisture. We have clouds that are starting to form at 300 feet.”
Humidity levels throughout the region were expected to exceed 50%. In the South Bay, it could rise above 80%, according to forecasters.
“It’s a wet heat,” Murdock said. “There’s no getting around it.”
There also is no getting around the fact that the blistering temperatures are expected to drop significantly in most areas of the region by Sunday. A low-pressure trough continues to migrate toward the region from the Gulf of Alaska, and forecasters said it is stronger than the current high-pressure ridge.
The cooldown will begin Saturday, as temperatures fall from the 100s and high 90s in the hottest spots to the lower to mid-90s.
“That trough will be moving this out of the way, as we head into the weekend,” Murdock said. “That ridge has held on about as long as it can.”
Seasonal temperatures are expected to take hold as the next work week begins, and Murdock said they may lock in without a lot of increase in the days after that.