The National Weather Service in San Diego issued an extreme heat watch early Wednesday for San Diego County valleys, with dangerously hot conditions possible from Friday morning through Wednesday evening. Forecasters said highs on the hottest days could range from around 90 near the coast to the upper 90s and 108 degrees in the valleys.

The watch also points to warm overnight conditions, with coastal areas into the western valleys expected to stay in the lower to mid-70s over the weekend and into next week. The weather service said heat-related illnesses increase significantly during extreme heat events.

For Santee residents, the alert covers the weekend and the first part of next week. The National Weather Service says the long-duration heat wave could continue through much of next week, with moderate or greater HeatRisk for the coast and valleys and major to extreme HeatRisk for inland coastal areas into the western valleys.

The National Weather Service advises residents to drink plenty of fluids, stay in an air-conditioned room, stay out of the sun and check up on relatives and neighbors.