Ninety-degree weather and high humidity persisted Friday on the third day of the Ann Arbor Art Fair and the fourth day of a heat wave that’s lingered in the area.

Medics had transported four people from the Ann Arbor Art Fair to the hospital for treatment of heat-related illnesses as of 3 p.m. Friday. Huron Valley Ambulance crews did not respond to any reports of heat-related illness Friday outside of the art fair.

Ann Arbor Art Fair patrons have been sweating it out through the 2013 fair, as temperatures have been consistently in the 90-degree range for the first three days of the four-day event.

Melanie Maxwell | AnnArbor.com

Huron Valley Ambulance crews transported three people to the hospital on both Wednesday and Thursday for heat-related illnesses from the fair.

Health officials advise people spending time outside during the hot weather to stay hydrated, even when they don’t feel thirsty. Dehydration is the first step the progression to heat stroke.

Officials have also cautioned people to take care to keep their pets cool and sufficiently watered during the heat as well. Animal cruelty officers with the Humane Society of Huron Valley have not received reports of animals left in vehicles during the hot weather for the past two weeks, said Deb Kern, marketing director for the organization.

The hot weather this week prompted the National Weather Service to issue a heat advisory at noon Tuesday and to upgrade it to an excessive heat warning, which expires at 8 p.m. Friday.

There’s a chance of severe thunderstorms Friday night for much of southeast Michigan, as a front is expected to move across the state to break the heat wave.

Storms would be capable of producing torrential rain and one-inch-diameter hail, and would likely hit the Ann Arbor area after 9 p.m. according to the National Weather Service.

The Ann Arbor Art Fair closes Friday at 9 p.m.

Temperatures Saturday are expected to reach a high of 83 to 87 degrees.

Amy Biolchini covers Washtenaw County, health and environmental issues for AnnArbor.com. Reach her at (734) 623-2552, amybiolchini@annarbor.com or on Twitter.