The National Weather Service in San Diego upgraded inland San Diego County valleys to an Extreme Heat Warning early Thursday, warning of dangerously hot conditions from 10 a.m. Friday through 8 p.m. Thursday, Oct. 8.

Forecasters said high temperatures in the warning area are expected to reach the upper 90s to 106, with very warm nights mostly in the upper 60s to mid-70s. The warning covers San Diego County Inland Valleys, which includes Santee.

The weather service said heat-related illnesses increase significantly during extreme heat events.

For Santee residents, the warning means the hottest stretch is expected to include the weekend and several weekdays. The National Weather Service advises people to drink plenty of fluids, stay in air-conditioned rooms when possible, stay out of the sun and check on relatives and neighbors.

The agency also warned that young children and pets should not be left in unattended vehicles because car interiors can become lethal within minutes.