The heat wave Santee residents have been warned about is no longer a forecast — it is here. The National Weather Service San Diego office confirmed Sunday that warming has begun, with high temperatures running 15-20 degrees above normal today and expected to increase further through the week.

A Heat Advisory will be in effect for coastal areas and inland valleys from 10 a.m. Monday through 8 p.m. Friday. An Extreme Heat Watch is in effect for the mountains and low deserts beginning Thursday at 10 a.m. through Friday at 8 p.m. By Thursday and Friday, forecasters are calling for highs near 100 to 101 degrees in Santee and surrounding East County communities — an especially notable feat for mid-March with potential to break monthly high temperature records.

Overnight lows will offer some relief, dropping into the mid-to-upper 50s most nights. That said, the persistent warmth can still be dangerous for those without adequate cooling during the day.

Health officials are warning of a high risk for heat-related illnesses affecting people, pets, and livestock. Residents are urged to stay well hydrated, limit outdoor activity during the hottest parts of the day (typically noon to 6 p.m.), and check on elderly neighbors and family members. Those without air conditioning can visit a San Diego County library, community center, or indoor shopping mall.

For updates and cooling center locations, visit the San Diego County Office of Emergency Services or call 2-1-1. The NWS San Diego office will issue updated advisories as conditions evolve throughout the week.