With triple-digit temperatures forecast in both L.A. and Orange counties today, a heat advisory indicating temperatures may be hot enough to make some people ill will be in force in much of the Southland from this morning until Thursday evening.

The heat advisory will be in effect from 10 this morning until 8 p.m. Thursday in the Santa Monica Mountains and the San Fernando, Santa Clarita and San Gabriel valleys, beach cities, metropolitan Los Angeles and the Hollywood Hills, and inland Orange County, with the National Weather Service forecasting highs of between 100 and 106 in those areas, with the hottest temperatures occurring on Wednesday.

The forecast for Long Beach is 90 degrees today, 97 degrees on Wednesday, 90 degrees on Thursday and 86 degrees on Friday.

“Hot temperatures may cause heat illnesses to occur,” warned the NWS. “Drink plenty of fluids, stay in an air-conditioned room, stay out of the sun, and check up on relatives and neighbors. Young children and pets should never be left unattended in vehicles under any circumstances.”

No red flag warnings were in effect today—a red flag warning in the San Gabriel Mountains and the Santa Clarita Valley expired around 5 p.m. Monday—but the weather service warned of near-critical fire conditions through Friday amid Santa Ana winds gusting at 35-40 miles per hour and single-digit humidity levels.