Autumn is on hand but summer heat hanging out

As expected, the commencement of autumn is set to bring with it an ever-so-brief rendezvous with some intense summer heat — at least during the daylight hours.

“It will cool off quite nicely at night,” National Weather Service meteorologist Roger Gass said Tuesday. “We’re going to get some moderate heat across the interior, but the overnight lows will allow it to cool off. So once the sun goes down, it will be nice.”

The sun will be going down a little more than two minutes earlier each day now that autumn has arrived, the weather service said. The season officially begins at 5:05 p.m. Tuesday.

Temperatures were expected to be about 3-5 degrees warmer Tuesday than they were on Monday, but the real spike in the heat is expected Wednesday. High pressure is expected to build significantly on Wednesday and a bit more on Thursday, lifting the temperatures with it.

The hottest temperatures Wednesday are likely to be in the upper 80s in the far interior areas such as Concord, Livermore and Dublin. In the South Bay, San Jose is expected to reach the mid-to-low 80s. Oakland and San Mateo are likely to get into the mid-70s.

Those temperatures are expected to maintain through Thursday. On Friday comes another big dip into temperatures similar to what the region experienced over the past weekend.

“We’re expecting the high pressure over the Eastern Pacific Ocean to build into the region over the next couple of days,” Gass said. “Then it starts to flatten out as we get to the weekend. It’s not a very strong ridge.”

As a result, it is not expected to compress much of the marine layer. The layer of fog is expected to reach into the interior by Friday. It remained thick enough that coastal drizzle may continue to fall near the coast overnight and in the mornings even as the thermometer briefly climbs.