June 27, 2012 (CHICAGO) (WLS) — Temperatures in Illinois are forecast to top 100 degrees by Thursday, and authorities are urging the public to be cautious.

Health officials and the City of Chicago are reminding people to keep cool as this heat wave begins.

The city will open public cooling centers, including at all 79 Chicago Public Library locations. All the city’s public parks, pools and beaches are open.

Wednesday’s heat advisory goes into effect at noon and remains in place until 8 p.m., according to the National Weather Service’s Chicago office.

The weather service estimates that Thursday’s high could range from 100 to about 105 degrees, and the heat index could hit up to 110 degrees. The all-time high for June 28 is 101 degrees, which was set in 1952. Temperatures haven’t hit 100 since July 24, 2005, when it was 102.

As the temperatures heat up, city and county officials are trying to prepare residents for the dangerous heat that’s expected Thursday.

“The people who are most vulnerable are the very young and the very old. We encourage to check on them,” said Cook County Hospital Dr. Robert Feldman.

Dr. Feldman says, when we sweat in high heat and humidity, evaporation slows and the body has to work harder to maintain a normal temperature.

“It’s important to listen to your body,” said Dr. Feldman. “If you’re feeling lousy, get out of the heat, take it easy.”

Wearing light and loose fitting clothing, drinking plenty of water and rescheduling strenuous activities to the early morning or evening can help reduce the risks of sunstroke, heat cramps and heat exhaustion, the weather service said. It’s therefore recommended that anyone who must work outside or is exercising outdoors limit their activity between 10 a.m. to 3 p.m., when it’s usually hottest.

“If you notice they are weak, dizzy confused, get them out of the heat,” said Dr. Feldman. “If after a few minutes they remain confused then it’s time to get medical attention.”

After weeks of repair work to get all the district pools up to code, Hamlin Park became the last of the district’s 50 public pools to open Wednesday.

“We’ve been waiting a couple of weeks for this to happen,” said Julie Mintun.

“I freeze my water bottles the night before so they are icy cold and make sure I know where the fountains are to refill and hydrate frequently,” said Jenny Khalaf, who was biking on the lakefront.

Chicago has had 14 days reach the 90s this year so far, with May 27 being the warmest day at 97 degrees.

Suburban campers beat the heat

Hundreds of day campers at Gurnee’s Viking Park stayed cool Wednesday with water activities.

“We change up the activities based on the temperature, make them a little less strenuous,” said Lisa Sheppard , Gurnee Park District. “We have a track and field day, we won’t do all the running events. We will scale those back and do some other things and we add a lot more water activities.”

The kids may not seem bothered by the heat, but their counselors are paying even closer attention with the extremely high temperatures.

In LaGrange, youngsters at Camp Mighty Munchkins kept busy indoors.

“All our activities will be in the shade,” said Ross Houston, Park District of LaGrange. “We will never keep them in direct sunlight. Most of the activities are going to be inside on days like that. You know, it’s for their safety. It’s very important.”

Campers will be limited to outdoor activity Wednesday and Thursday. The LaGrange Park District’s has an air conditioned building in the corner of Gilbert Park packed with props for a day full of indoor adventures.

For those watching gardens wither under the crushing heat, Sharon Yiesla, a plant clinic assistant at the Morton Arboretum, recommends focusing on getting new plantings appropriate water and putting the lawn last.

“They go dormant when it is hot and dry so we can allow that to happen,” said Yiesla. “Unless we have a long extended bad drought, they won’t dry. They will come back when the rain comes back and the cooler temperatures come back. I urge people to not be spending a lot of time watering their lawn.”

The Sun-Times Media Wire contributed to this report.