Temperatures will reach well into the triple digits again Thursday in the San Diego County deserts, according to the National Weather Service.
Conditions in the rest of the county will also remain warm, but will be slightly cooler than Wednesday.
A cooling trend will continue throughout the region until early next week, forecasters said.
A heat advisory is in effect until 9 p.m. Friday in the western valleys and an excessive heat watch will also last until 9 p.m. Friday in the deserts.
Temperature records for a May 6 were set in Borrego Springs and tied in Campo on Wednesday, during what was expected to be the hottest day of the week.
The 109-degree high in Borrego Springs broke the previous record for that date of 105, set in 1989, according to the National Weather Service. Records date back to 1965.
The mercury reached 95 in Campo, tying the record set in 1989. Records date back to 1943.
High temperatures Tursday are forecast to reach 80 degrees near the coast, 87 inland, 93 in the western valleys, 93 in the mountains and 110 in the deserts.
Nighttime lows are expected to remain in the low- to mid-70s through Saturday in the county deserts, meaning the minimal cooling at night could pose a health risk to those who don't have access to air conditioning because the body needs time to cool down from the day's heat, according to the NWS.
The combination of hot days and warm nights is expected to increase the threat of heat-related illness, and NWS officials urged residents to drink plenty of fluids, stay out of the sun and check up on relatives and neighbors.
Also, young children and pets should be never be left unattended in a vehicle, with car interiors able to "reach lethal temperatures in a matter of minutes," according to the NWS.
