Dangerous heat is on the way. Doctors and first responders around Long Island say it needs to be taken seriously.

"Nineties to over 100 degrees. This is extremely dangerous, and we're asking people to do the following: curtail your outside activities. Don't think that you're immune to getting sick from heat exhaustion, from over exposure to the sun. This is serious business when it gets this warm," said Nassau County Executive Bruce Blakeman.

Medical professionals all over Long Island are urging people to be safe.

"The older and the younger are at much more susceptibility for any type of heat-related illness. People think it might take a couple hours for them to end up with any type of heat-related illness but really it can take as short as 15 minutes," said Dr. David Silver, with Northwell Health's Glen Cove Hospital.

If you start feeling lightheaded, get into an area with air conditioning and try to stay indoors, according to medical professionals.

But if you're still planning to be outside especially for the Fourth of July, stay hydrated and wear loose, light clothes.

"When you're barbecuing, that's a hot grill, the hot sun, make sure you're getting shade. Make sure you move over, take a break every now and then," said George Gorman, regional director of New York State Parks, Recreation and Historic Preservation Long Island.

Cooling centers are available in both Nassau and Suffolk counties.

That includes the former Nassau County Family Court, located at 1200 Old Country Road in Westbury, which will be open 24 hours.

Babylon Town Hall Annex, located at 281 Phelps Lane in North Babylon, will also serve as a cooling center.