An Extreme Heat Warning is in effect for inland San Diego County from 10 a.m. Wednesday through 8 p.m. Thursday, according to the National Weather Service in San Diego.

The warning covers the San Diego County valleys and mountains, along with inland Orange County, the Inland Empire, the Santa Ana Mountains and nearby foothill areas. The weather service said temperatures are expected to reach the 90s to near 100 in the San Diego County valleys, with Wednesday expected to be the hottest day.

For Santee, the NWS forecast calls for a high near 98 degrees Wednesday and about 94 degrees Thursday. Overnight lows are expected to stay warm, with Santee forecast near 73 degrees Wednesday night.

The weather service said heat-related illnesses increase significantly during extreme heat events, especially for people spending long periods outdoors. Residents are advised to drink plenty of fluids, stay in air-conditioned spaces when possible, avoid direct sun and check on relatives and neighbors.

Daytime outdoor recreation is discouraged during the warning period. Residents should also keep pets out of the heat and avoid leaving people or animals in parked vehicles, where temperatures can rise quickly.