The National Weather Service says high temperatures and high humidity will combine to create dangerous conditions in the Ann Arbor area this afternoon.

The Weather Service has issued a heat advisory starting at noon today and lasting until 8 a.m. Tuesday morning.

When the heat index climbs above 90 degrees, it's especially important to stay hydrated by drinking water or other fluids when exercising outdoors.

Lon Horwedel | file photo

The heat index will reach dangerous levels of 95 to 100, and overnight temperatures will only drop into the mid- to high 70s, providing little relief, the Weather Service said.

Although daily highs will climb into the low 90s through Wednesday, lower humidity is expected to make conditions more bearable after today, said Karen Clark, a meteorologist with the National Weather Service in White Lake.

The relative humidity (a measure of the amount of moisture in the air) is expected to be around 50 percent, Clark said. That combination of high humidity and high temperatures can mean dangerous conditions for people outside or who don’t have air conditioning.

Clark advised anyone working or exercising outside to take it easy. “Just be careful today. Drink plenty of water. Try to limit the time in the heat. Maybe take some breaks.”

She said the heat can be particularly hard on the elderly and young children, and pets left outside can be affected as well.

The weather service forecasts a high of 89 to 93 today. That’s not likely to break any records. The record high for today in the Detroit area is 96, Clark said. High temperatures in the low to mid-90s are expected both Tuesday and Wednesday. High temperatures are expected to drop back into the low 80s by Friday, she said.

Possible thunderstorms are in the forecast for Wednesday and Thursday.

Contact Cindy Heflin at cindyheflin@annarbor.com or 734-623-2572.