LOS ANGELES — Temperatures continued soaring Tuesday across much of Southern California as a mini-heat wave brought triple-digit highs to some areas, but a major cool-down is expected to arrive by later in the week.

National Weather Service forecasters noted that Tuesday’s temperatures were actually running between 1 and 3 degrees cooler than Monday, thanks to a slight increase in onshore flow.

“Still very hot though and excessive heat warnings and heat advisories remain in effect across all the valleys and mountains as well as the interior coastal plain,” according to the NWS. “Onshore flow is expected to increase again Wednesday, cooling things off another 5 or so degrees on average across coast/valleys. No so much farther inland though.”

An excessive heat warning will be in effect until 8 p.m. in the San Fernando and San Gabriel valleys, along with Calabasas and Agoura Hills, where temperatures could reach as high as 108 degrees, with overnight lows falling only into the 70s or 80s.

A less severe heat advisory was extended through 8 p.m. Wednesday in the San Gabriel Mountains and Antelope Valley (14) Freeway corridor, with highs ranging up to 105 degrees.

Most of Orange County will also be under a heat advisory until Wednesday night.

But a heat advisory in the Santa Clarita Valley, Palos Verdes Hills, L.A. County inland area including downtown, and the Santa Monica Mountains Recreational Area will expire at 8 p.m. Tuesday. Highs in those areas could reach 105 degrees.

Long Beach Airport reported a record high temperature of 97 degrees on Monday, breaking the mark set for that date in 1995, when the high was 96.

But while temperatures are running as much as 10 degrees above normal Tuesday, things will start too slowly cool down Wednesday. By Thursday and Friday, a trough of low pressure is expected to move in, bringing more onshore flow and below-normal temperatures.

“Temperatures in most areas will drop below normal levels by Thursday and as much as 5-15 degrees below normal by Friday, with valley areas only in the upper 70s and 80s, a good 20 degrees cooler than today,” according to the NWS.

The cooler conditions are expected to last into the Labor Day weekend. Forecasters said the deepening marine layer could also increase the chance of some morning drizzle in select locations. The low-pressure trough is expected to move out of the area starting Sunday, beginning a warming trend, but temperatures will “remain below normal at least through Monday.”

But the heat remains on, cooling centers will be available across the area for those looking to escape the high temperatures. The city of Los Angeles was operating six cooling centers Tuesday, open from 10 a.m. to 9 p.m. at:

— Lake View Terrace Recreation Center, 11075 Foothill Blvd.

— Mid Valley Senior Center, 8825 Kester Ave.

— Sherman Oaks East Valley Adult Center, 5056 Van Nuys Blvd.

— Lincoln Heights Senior Center, 2323 Workman St.

— Fred Roberts Recreation Center, 4700 Honduras St.

— Jim Gilliam Recreation Center, 4000 S. La Brea Ave.

Angelenos can find respite from the heat at all Recreation and Parks facilities and library branches during their normal business hours, Mayor Karen Bass said. For location and hours, see laparks.org/reccenter and www.lapl.org/branches.

Climate stations were operating in Skid Row as free, designated areas for residents there to stay cool. Urban Alchemy staff will offer cold beverages, seating and activities, she said. They are on Towne Street (between Fifth and Sixth streets), across the street from the ReFresh Spot and San Pedro Street between Sixth and Seventh streets.

Bass added that the Mayor’s Office of Public Safety was working to coordinate with the Emergency Management Department, Los Angeles police and fire departments, Recreation and Parks, Los Angeles Department of Water and Power and other city Departments to ensure all departments are ready to respond to the heat wave.

The NWS advised people to drink plenty of fluids, stay indoors if possible in an air-conditioned room, and check up on relatives and neighbors.

Children and pets should never be left inside vehicles without air conditioning for any length of time, as death could occur in minutes when temperatures are this high.

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