SAN FRANCISCO (AP) — California's siege of wildfires has significantly quieted but forecasters warned Tuesday that a fall heat wave will bring back high fire danger this week.

Red Flag warnings were to go into effect in much of Northern California before dawn Wednesday due to high pressure producing hot and dry conditions with offshore gusts, the National Weather Service said.

The foremost concern was "the likely development of critical fire weather conditions by Wednesday morning, and then becoming even more extreme Wednesday night into Thursday," the service's San Francisco Bay Area office wrote.

Pacific Gas & Electric said it is likely some circuits will be turned off starting Wednesday evening to try to prevent fires from being started by damaged power lines. An estimated 50,000 customers in parts of 21 northern counties would be affected, the utility said.

Southern California, which started the week with triple-digit high temperatures, is predicted to see particularly strong northeast winds Friday.

More than 8,500 wildfires have burned well over 6,406 square miles (16,591.4 square kilometers) in California since the start of the year, but mostly since mid-August. Thirty-one people have died and more than 9,200 structures have been destroyed.

Most of the huge fires have been fully or substantially contained over the past eight weeks but 11,500 firefighters remain on the lines.

Numerous studies have linked bigger wildfires in America to climate change from the burning of coal, oil and gas. Scientists say climate change has made California much drier, meaning trees and other plants are more flammable.