"The most extreme heat should be through by Friday evening," National Weather Service meteorologist Brian Tentinger said.
Heat watches are issued to highlight the risk of hot weather, especially for the elderly and others who might be more sensitive to heat.
Cities throughout the Bay Area are expected to have high temperatures, but Tentinger said some of the "hotspots" will be in the Salinas Valley, North Bay valleys and some East Bay areas such as Livermore and Pleasanton.
"Some areas today could reach record highs," said Tentinger, who pointed out that Oakland is forecasted to hit 90 degrees today, one degree over its record high for the day.
San Jose, where an excessive heat warning has been issued, is forecasted to tie its record high for the day of 94 degrees.
"It seems like most of the records that get up this high occur in the summer or in the fall," Tentinger said.
A heat advisory has been issued for San Francisco, where temperatures in parts of the city are expected to reach 91 degrees Thursday, according to Tentinger.
In Mountain View, an excessive heat warning is in effect today between noon and 8 p.m., the city announced.
The weather service issues excessive heat watches, excessive warnings and heat advisories when a prolonged period of dangerously hot temperatures is expected. Weather service officials are warning residents to drink plenty of fluids, stay in air-conditioned rooms, stay out of the sun and check up on relatives and neighbors.
In addition to the national weather service, county officials are advising residents to take precautions against the extreme heat.
The San Mateo County Health Department announced that local temperatures are expected to climb into the 90s and is reminding residents that a heat wave in the summer of 2000 caused several deaths.
The county's health department recommends residents stay indoors in the coolest part of the house, especially between noon and 6 p.m., and wear lightweight, light-colored, loose-fitting clothing.
Contra Costa Health Services officials issued a list of warnings to residents, recommending they curtail outdoor activity and avoid hot cars, where temperatures can reach 150 degrees after 20 minutes. Temperatures in parts of the county are expected to exceed 100 degrees.
In Santa Cruz, health officials are reminding residents that while electric fans may provide comfort, they will not prevent heat-related diseases.
According to the county's health services agency, heat stroke is the most common heat-related illness and some symptoms include red, hot dry skin, a strong pulse, throbbing headache, dizziness and nausea.
Tentinger said the heat wave has not prompted officials to issue a red flag warning for the Bay Area, which is made when strong winds and dry weather conditions create a threat of fire.