Steamy Bay Area heat wave expected to peak at mid-week

A steamy hot wave that has been building steadily and gaining some of its strength from monsoonal moisture more common to the desert climate is expected to peak in the Bay Area by mid-week, and the National Weather Service said a few drops of rain may fall during the process.

Any rain that may fall is expected to be miniscule and is likely to be limited to areas near the coastline, according to the weather service. As it is, that chance for rain is “about 10% or less,” NWS meterologiste Karleisa Rogacheski said.

Still, that small percentage speaks to the nature of the heat in the region — namely that there is more than a hint of moisture mixed in with the heat. Unlike most Bay Area heat waves, the temperatures are expected to be mixed with a humidity level that will be threaten 40% on Monday and closer to 30% Tuesday and Wednesday in the far interior places.

By then, the temperatures there are expected to be in the upper 90s in the hottest interior places, and in the upper 80s and low 90s in the South Bay.

The region got a glimpse of that heat over the weekend. In Salinas, the hot temperature of 82 degrees came matched the same mark previously reached in 1999, 1979 and 1954 and came mixed with a humidity that was higher than 70%, according to the weather service.

All of it is being caused by a massive heat dome centered near the Great Basin that is causing southern monsoonal moisture to be redirected toward the region. That dome is fueling a dangerous heat wave in much of the western part of the United States.

Closer to the South Bay and near the water, the humidity is also expected to be high. San Jose was expected to reach 88 degrees on Monday, with the humidity topping 60%. The humidity is expected to be the same in Oakland and San Mateo, where the thermometer is expected to reach the upper 70s.

In San Francisco, the humidity is expected to hover between 80% and 90% as the temperatures creep into the low 70s.

“The chances are small,” Rogaceski said. “But we might see some fast-moving, very light showers. A couple-hundredths of inches at the most.”

More likely, the ground is likely to stay dry and any rain that is generated will disintegrate by the time it hits the ground, she said. Those conditions also could create more potential for dry lightning, though Rogacheski said those chances also are likely to be 10% or less.

The weather service said it did record lightning strikes on Sunday but that all of them were over the Pacific Ocean.

Coastal flooding also will remain a threat through the early part of the week, as king tides continue to pound the Bay Area coast, and the Pacific Ocean swells stay high because of storm activity in the Southern Hemisphere. A coastal flood advisory remains in effect through Thursday along the Bayshore locations and through Saturday along the Pacific Coast.