The Baltimore City Health Department issued this year’s first “Code Red Extreme Heat Alert” as the city faces a heat index exceeding 100 degrees Fahrenheit on Thursday and Friday.

The code red alert is issued when temperatures are “severe enough to present a substantial threat to the life or health of vulnerable Baltimore residents,” the health department said in a published statement on Wednesday.

“The fact that we're located in an urban area makes things worse because of population density and the presence of heat absorbent asphalt,” Acting Commissioner of Health Mary Beth Haller said in the statement.

The city health department urged Baltimore residents to check in on elderly and sick loved ones, and to keep children and pets out of the heat as much as possible. Everyone is encouraged to drink plenty of water and stay indoors.

The health department’s division of aging opened six cooling centers across the city to provide shelter from the heat.

Mary Parker-Collins, the manager at Sandtown Winchester Senior Center, said a group of 57-to-69-year-olds gathered today for access to air conditioning that they don’t have in their own homes.

“Some of them may have central air, and some of them, they just have fans,” Parker-Collins said. “So if they don’t want to stay in their house, they will come out and sit in the cooling center for some type of activity.”

The Mayor’s Office of Homelessness Services and the Housing Authority of Baltimore City also opened three cooling centers collectively.

Baltimore County’s health department sent out an emailed warning this afternoon, citing “extremely high temperatures” in the coming days. The department reminded county residents about available air conditioning in public libraries and community centers.

The city health department warned local residents to monitor symptoms of heat exhaustion, such as nausea and flushed or clammy skin, and to seek medical help if symptoms occur.