The alert, issued by the Bay Area Air Quality Management District, means that air quality is expected to be poor and residents are advised to reduce driving and avoid outdoor activities during the hottest parts of the day.
An alert is already in effect today. Sunday's smog alert is the ninth of 2012.
Residents in the East, North and South bay regions are advised to be particularly mindful of ozone pollution, officials said.
The alert often coincides with warm weather but other factors contribute to poor air quality, officials said.
Ozone can cause throat irritation, congestion, chest pain and inflammation of the lining of the lungs. Those with asthma, bronchitis and emphysema are especially vulnerable, as are young children, seniors and those with respiratory and heart conditions.
Residents are asked to avoid driving on Spare the Air days and find alternate transit options, including biking, carpooling or taking public transit.
There is no free transit offered, and a no wood-burning ban is in place.
Sunday's forecast includes temperatures reaching into the upper 90s and lower 100s inland and into the 70s and lower 80s along the coast as part of a rapid warm-up expected in the area through Tuesday, according to the National Weather Service.
In anticipation of the heat wave, Morgan Hill police posted an online notice about a cooling center open today and through the next few days at the Centennial Recreation Senior Center at 171 W. Edmundson Ave. in Morgan Hill.
The center will be open today until 8 p.m.
On Sunday the center will be open between 8 a.m. and 6 p.m. for residents to take a break from the heat and during weekdays between 5 a.m. and 10 p.m.