The Bay Area is in for a scorching start to autumn, with the National Weather Service forecasting temperatures to soar into the triple digits this week.

The heat wave is set to begin on Monday, with temperatures expected to reach the mid-to-high 90s in the hottest spots. The mercury is expected to continue to climb, peaking on Wednesday when inland areas are forecast to reach at least 105 degrees. Temperatures will remain extremely hot until at least Thursday, with the heat expected to stay inland and in upper elevations all week.

The Bay Area won't be spared from the heat either. San Jose and Morgan Hill are expected to reach at least 96 degrees on Monday and will likely surpass 100 degrees on Tuesday and Wednesday. San Mateo and Oakland are forecast to be in the upper 80s on Monday and will reach the mid-90s by mid-week. San Francisco is expected to reach the 90s on Tuesday.

The heat is expected to be 15-25 degrees higher than average, and a heat advisory has been issued for the entire region and Central Coast from Monday to Wednesday. A Spare the Air Alert has also been issued.

The heat wave is being caused by high pressure aloft and an upper low that cooled the area off over the weekend moving out. This is also causing off-shore winds to blow Monday morning, which is enhancing the heat and temperatures, especially along the coast.

The off-shore winds can also contribute to dangerous fire conditions, and PG&E has warned customers that it may shut off power in parts of Alameda and Contra Costa counties due to the heat wave. The utility is part of the Public Safety Shutoff Program, which preemptively shuts down power in areas that reach a certain threshold of fire risk.

However, the good news is that the surface high pressure that is creating the off-shore winds is expected to move out of the area on Wednesday, bringing cooler temperatures to the Bay and coast on Thursday and Friday.

Red hot start to October expected

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