(KRON) -- A fire watch issued for much of the Bay Area on Monday has been upgraded to a red flag warning, according to the National Weather Service. The warning will take effect Thursday at 11 p.m. and last through 5 p.m. Saturday. The NWS is warning of critical fire weather conditions during that time period. Offshore winds are expected to be between 25 to 35 mph with gusts up to 45 mph. Isolated gusts of up to 65 mph are also possible across the highest terrain and ridgetops. What is a fire weather watch? With daytime relative humidity as low as 10%, critical fire weather conditions are "likely or imminent," according to the NWS. Critical conditions include low humidity, strong winds and dry fuels. Graphic: NWS This week's red flag warning impacts almost all of the Bay Area and stretches down into the Central Coast, including the City of San Francisco, the SF Peninsula Coast, and the SF Bay shoreline. The NWS is cautioning residents of easier fire starts and potential for rapid fire spread. People are being advised to exercise fire safety precautions, have an emergency plan in case a fire starts near you, and to stay in touch with local officials for the most up-to-date information.