Harford County's departments of community services and parks and recreation opened several cooling centers Thursday from 8:30 a.m. to 9 p.m.

Residents could visit the Havre de Grace Activity Center at 351 Lewis Lane; the McFaul Activity Center, at 525 West MacPhail Road in Bel Air; and the Veronica "Roni" Chenowith Activity Center, at 1707 Fallston Road in Fallston.

County Executive David Craig encouraged residents, especially the elderly, young children and those with respiratory health issues, to take shelter from the heat.

The county health department noted that the state issued a heat emergency plan and is warning residents to be cautious in excessive heat.

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"Prolonged heat exposure can result in recreational as well as occupational illnesses and injuries. Persons who work or recreate outside in direct exposure to the sun, or indoors in excessive heat for any extended period of time must be particularly mindful of the risks and be exceptionally careful," health officer Susan Kelly said in an advisory from the department.

The health department warned that immediate medical attention should be sought for anyone whose body temperature is above 104 degrees and who has symptoms of confusion, combativeness, strong rapid pulse, lack of sweating, dry flushed skin, faintness, staggering or delirium or coma, especially with an older adult.

More information is available at http://dhmh.maryland.gov/extremeheat or from the Harford County Health Department website at http://www.harfordcountyhealth.com or by calling 410-612-1781.

The National Weather Service said there could be a slight chance of showers and thunderstorms after midnight Thursday. The 100-degree mark for temperatures was eclipsed by midafternoon

Friday temperatures might be headed down a little. The NWS high is forecast near 91.

Intern Mariel Stratford contributed to this article.