Credit: National Weather Service Milwaukee

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Potentially deadly heat indexes in excess of 100 degrees are expected in some areas of south-central and southeastern Wisconsin Thursday and Friday, according to an excessive heat warning issued Wednesday by the National Weather Service in Sullivan.

Daytime temperatures in the low-to-mid 90s are expected Thursday and Friday. However, the heat index, which factors in relative humidity, is expected to top out at 104 to 110 on Thursday and 98 to 103 on Friday, according to the weather service.

"Take precautions if you need to be outdoors, especially with physical activity," said Sean Miller, a meteorologist with the National Weather Service in Sullivan.

"Stay hydrated, seek shade and never leave kids or pets in vehicles because vehicles can get so hot so fast."

The last time an excessive heat warning was issued for the region was in July 2012.

The weather service warned of possible heat-related illness and said people on certain medications will be more affected by the heat and should take extra precautions to remain cool.

People should drink plenty of fluids and check on relatives and neighbors, especially the elderly and young children. Any strenuous activities should be rescheduled to early morning or evening hours, according to the weather service.

The weather service also urged residents to know the symptoms of heat exhaustion and heat stroke and wear lightweight loosely fitting clothing.

According to the Center for Disease Control and Prevention, signs of heat exhaustion include heavy sweating; a weak pulse; vomiting; nausea; and cold, pale skin. Signs of heat stroke include a body temperature above 103 degrees; hot, red skin; a rapid pulse; and in some cases unconsciousness.

Milwaukee public libraries will remain open until 8 p.m. Thursday and Friday, and the Milwaukee Water Works has made water sprinklers available at "Cool Spots" at several Milwaukee Public Schools playgrounds.

The Cool Spots are open from noon to 5 p.m. weekdays when temperatures are predicted to hit 85 degrees or higher, or when the city issues a heat advisory. They can be found at:

■ Ben Franklin Elementary School, 2308 W. Nash St.

■ Carmen Playfield, 7320 W. Carmen Ave.

■ Clinton Rose Park, 390 W. Chambers St.

■ Franklin Square, 2643 N. 13th St.

■ Columbia Playground Cool Spot, 1354 W. Columbia St.

The Wisconsin Department of Health Services also is designating dozens of "cooling centers" — public buildings and other facilities residents can go to cool off — throughout the region. Centers in Milwaukee County include:

■ The Brown Deer Library, 5600 W. Bradley Road, (414) 357-0160.

■ The Kelly Senior Center, 6100 S. Lake Drive, in Cudahy, (414) 481-9611.

■ The Greenfield Public Library, 5310 W. Layton Ave., (414) 321-9595.

■ The Shorewood Public Library, 3920 N. Murray Ave., (414) 847-7620.

■ The Salvation Army, 8853 S. Howell Ave., in Oak Creek, (414) 762-3993.

Cooling sites in Waukesha include the Hebron House shelter at 812 N. East Ave and Jeremy Safe Haven at 1301 E. Moreland Blvd. Both will remain open all day Thursday and Friday.

The complete statewide list of cooling centers is available online at https://www.dhs.wisconsin.gov/preparedness/cooling-sites.pdf. Residents also can call 211 for heat-related health and safety information.

The Wisconsin Department of Transportation reminded drivers Wednesday of the potential for pavement buckling during the hot and humid weather. The agency asked drivers to call 911 to report serious pavement issues, and to move over for highway crews repairing damaged roads.

The Public Service Commission of Wisconsin also advised residents to keep temperatures low and save energy by closing blinds, unplugging electronics when they are not in use, washing clothes and dishes in the morning before it gets too hot and making sure air conditioners are clean.

The Wisconsin Department of Agriculture, Trade and Consumer Protection also warned residents that heat strokes can be fatal for pets and livestock. Signs of heat stroke in small animals include panting or breathing difficulty, a rapid heartbeat, vomiting, and collapsing, it said.

Jessie Bekker of the Journal Sentinel contributed to this report.