A wave of thunderstorms and hail could hammer the Big Apple on the Fourth of July as a vicious five-day heat dome cooks revelers in nearly 100-degree swelter – making the holiday the hottest in nearly 20 years.

Independence Day festivities Saturday afternoon and evening are in the crosshairs of the potential torrential rains, damaging winds and hail as temperatures are set to hit 95 degrees – the hottest July 4 since 2010, when the city baked under a blistering 96 degrees, AccuWeather senior meteorologist Matt Benz told The Post on Tuesday.

Last year, Gotham rang in the Fourth under 83-degree heat.

Benz said this holiday’s wet, humid nightmare is expected to begin sometime Friday night and keep it up through the weekend.

“When these heat waves start to break down, they tend to unleash thunderstorms, but the timing – especially this far out – is difficult to pin down,” he said, adding that forecasters are currently monitoring related storm systems in Canada.

“We’re still a ways out, but our forecast, at least for Saturday, we’re calling for a 40% chance of rain.”

The potential downpours are set to arrive at the tail end of a brutal heat wave that will scorch New York City with 95-degree heat Wednesday and around 100 Thursday and Friday before easing into the low 90s on Sunday.

Real-feel temperatures will hover between 105 and 110 degrees in the afternoons during the five-day stretch, as scorching conditions and humidity surge, according to AccuWeather.

Temperatures will only drop to around 80 degrees overnight during the heat dome.

“That’s what will make this especially dangerous,” Benz said.

“We focus on the high temperatures, but it’s the overnights, especially if you don’t have AC, where it just becomes tight, like when we’re sleeping.”

Benz urged people – especially Fourth of July crowds – to drink plenty of water when outdoors, watch the forecast, conserve energy and stay inside when possible. 

Large-scale events are taking place in and around the city as part of the celebrations marking America’s 250th anniversary of the signing of the Declaration of Independence. 

Highlights include Saturday’s Sail4th 250 & Macy’s Fireworks up the Hudson, which will bring crowds to the waterfront in Manhattan, Brooklyn and New Jersey.

The National Weather Service has issued an extreme heat watch from noon Wednesday through 9 p.m. Saturday in New York City, the Lower Hudson Valley, Long Island, northern New Jersey and western Connecticut.

An extreme-heat warning was also issued from noon through 9 p.m. Wednesday.

New York Gov. Kathy Hochul said the state is also closely monitoring the heat wave and coordinating efforts involving cooling centers while watching the state’s electrical grid.

“This week will bring dangerous heat all across the state, and my administration is taking action to ensure New Yorkers can safely enjoy our historic summer of activities,” Hochul said in a press release.

“New Yorkers should take the proper precautions to protect themselves and their families by staying hydrated, limiting time outdoors, and monitoring your local forecast. I also encourage everyone to check in on those most vulnerable and our elderly neighbors.”