The National Weather Service (NWS) extended its heat advisory for Hilliard and Franklin County through 8 p.m. Sept. 3. Heat index values between 100 and 105 degrees are expected.

The NWS Wilmington, Ohio, office originally issued the advisory to expire at 11 p.m. Wednesday, Sept. 2. The extension pushes it through Thursday evening as high temperatures and humidity persist across central Ohio, the Columbus Dispatch reported. Most of Ohio fell under some form of heat advisory through at least Thursday, Sept. 3.

The heat index was forecast to reach 103 degrees on Tuesday, Sept. 1, and is expected to stay above 100 through Thursday. Forecasts call for highs near 95 degrees both Wednesday and Thursday, with heat index values as high as 101 on Wednesday.

A heat advisory is issued when the heat index is forecast between 100 and 104 degrees. The NWS warns that hot temperatures combined with high humidity may cause heat illnesses.

The agency urged residents to drink plenty of fluids, stay in air-conditioned spaces, stay out of the sun and check on relatives and neighbors. Residents should wear lightweight, loose-fitting clothing and limit strenuous outdoor activity to early morning or evening hours.

The Ohio Department of Health identifies several high-risk groups during heat waves: infants, young children, older adults, people with chronic medical conditions such as heart disease or poor blood circulation, and people with mental illness, the Cincinnati Enquirer reported. Pregnant women, outdoor workers and anyone without air conditioning at home are also at higher risk.

The Central Ohio Transit Authority (COTA) offered free fares on all transit vehicles Tuesday, Sept. 1, and Wednesday, Sept. 2, while the original advisory was in effect. COTA typically suspends fares during NWS heat or cold advisories, though it was not confirmed whether free rides would extend through Thursday to match the new expiration.

The NWS advisory urges residents to act when they see symptoms of heat exhaustion and heat stroke. Forecasts show a chance of showers and thunderstorms Friday, Sept. 4, with a high near 90 degrees.