Thursday is forecast to be the hottest day of the summer so far in Baltimore, with temperatures reaching the mid-90s and humidity making it feel as hot as 105 degrees.
The National Weather Service issued a heat advisory until 8 p.m. for areas along and east of Interstate 95.
Meteorologists and health officials warned residents to be wary of heat-related illnesses like heat exhaustion and heat stroke. Symptoms include confusion, flushed skin and dry or cold and clammy skin, lightheadedness and nausea.
The Baltimore Health Department declared its first "Code Red" heat advisory of the summer, prompting the Mayor's Office of Human Services to open cooling centers across the city.
Temperatures are expected to reach 90 degrees by midday, and could reach 96 degrees, which would tie for the hottest temperature of the year so far.
Dew points are forecast to stay as high as 73 degrees, indicating oppressive levels of humidity. The dew point is the temperature to which the air would have to cool for condensation to form; through the summer months, it stays in the 60s on all but the most humid days.
The heat index, a calculation of how hot it feels based on both temperature and humidity, is forecast to reach its highest by late afternoon.
It hit 90 degrees downtown by 11 a.m., and at 1 p.m., it was 95 degrees with a heat index of 98 at the Inner Harbor, and 93 degrees with a heat index of 97 at Baltimore/Washington International Thurgood Marshall Airport, according to the weather service.
Showers and thunderstorms are possible overnight. Highs in the lower 90s are forecast Friday before highs drop back into the upper 80s, normal for this time of year, for the weekend.