SAN FRANCISCO (CBS SF) — The first day of summer brought warm weather to the Bay Area and triple-digit numbers across the Southwest.

In the East Bay, temperatures will be in the 90s Monday, and are expected to hit 100 degrees on Tuesday. Meantime, Southern California and much of the Southwest will continue to experience extreme heat.

The National Weather Service forecasts temperatures as high as 120 degrees in Phoenix and issued heat warnings for Tuscon, Yuma, the Grand Canyon and Lake Havasu.