A heat advisory has been issued until 7 p.m. Friday for Tuscaloosa County, according to the National Weather Service's office in Birmingham.

The heat index, a measurement of the combination of the temperature and the humidity, is expected to reach 105 degrees Friday afternoon. There's a 50 percent chance of showers and thunderstorms after 10 a.m., with rainfall between a tenth and quarter of an inch or higher. Friday night will be mostly cloudy with a 30 percent chance of showers and thunderstorms and a low near 75.

The National Weather Service offers these tips to avoid heat-related illnesses:

• Drink plenty of fluids, stay in an air-conditioned room, stay out of the sun, and check up on relatives and neighbors.

• Wear light weight and loose fitting clothing.

• Take extra precautions if you work or spend time outside. When possible, reschedule strenuous activities to early morning or evening.

• Anyone who works outdoors should schedule frequent rest breaks in shaded or air conditioned environments. Anyone overcome by heat should be moved to a cool and shaded location.

• Know the signs and symptoms of heat exhaustion and heat stroke.

• If you suspect someone is having a heatstroke, call  911.

The forecast calls for more of the same Saturday: High temperatures near 94 and a heat index again reaching 105. Chance of precipitation is 60 percent. Saturday night will be mostly cloudy, with a low around 76. Chance of precipitation is 40 percent.