Make sure to stay out of the sun this Friday, Baltimore.

The National Weather Service issued a heat advisory for the region, including Anne Arundel and Howard counties, starting 11 a.m. through late evening.

A “really humid air mass” is moving into the Baltimore area, said Brian LaSorsa, a meteorologist for the Baltimore/Washington office of NWS. The humidity will make the weather feel even hotter with a high heat index of 109. The advisory goes into effect until 8 p.m.

Heat is one of the deadliest forms of extreme weather. At least nine people have died from heat-related illness this summer, more than twice as many as at the same point last year, according to data from the Maryland Department of Health.

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LaSorsa said people should avoid exercising outside and going outdoors or opt to do so in the early morning or evening. Make sure to drink plenty of fluids throughout the day and check in on relatives and neighbors who may be more susceptible to heat illness.

The city issued a Code Red Extreme Heat alert starting Friday through next Tuesday. Cooling centers will be open to offer air-conditioned spaces and water. The weekend is forecasted for a high of 92 degrees on Saturday and 95 on Sunday, with chances of thunderstorms on both days.