LOS ANGELES — August is about to go out in a blaze of heat through much of California.

The National Weather Service says the heat wave will build Saturday and by Sunday excessive-heat watches or warnings will be in effect across Southern California and northward past San Francisco, excluding immediate coastal areas.

The Eastern Sierra and Central Valley will also feel the heat, with San Joaquin Valley counties also enduring poor air quality due to smoke from a wildfire.

Southern California valleys may reach triple digits Saturday, 105 Sunday and 110 Monday.

Los Angeles County Health Officer Dr. Jeffrey Gunzenhauser has declared a heat emergency for the San Fernando Valley effective Sunday through Wednesday, and a heat alert for downtown LA and the Antelope, San Gabriel and Santa Clarita valleys.