Long Island weather: Dangerous temperatures ahead as 'heat dome' spreads across region

Dangerous heat and oppressive humidity will descend on the entire region this week, bringing possible temperatures reaching the triple digits to parts of Long Island, forecasters said.

By Wednesday, a "giant ridge of high pressure" will be moving in from the southwest, according to Dominic Ramunni, a meteorologist with the National Weather Service in Upton.

Forecasters call the phenomenon a "heat dome."

The heat is expected to build over several days as this "large sprawling dome of high pressure" settles across the Northeast, Ramunni said. Temperatures Wednesday will be above 90, and then "we could be even making a run at triple digits, at least across partial parts of the Island as we go into Thursday and Friday," Ramunni said.

The National Weather Service issued a hazardous weather outlook for southern Connecticut, northeast New Jersey, and southeast New York. "The combination of heat and humidity could lead to heat index values from 95 to 110 degrees," the service warned.

On the East End, the heat will not be quite so oppressive; temperatures will likely top out in the high 80s or low 90s.

The evenings across the island should bring some relief, as temperatures are expected to drop to the high 70s.

"This is dangerous heat," Ramunni said, noting that more people die in extreme heat than in any other type of weather disaster including flooding, hurricanes and tornadoes.

People should "take it seriously," he said, "stay hydrated, take breaks in the shade if you're going to be spending any time outdoors."

Wearing loose, light-colored clothing can help you stay cool. "Of course, never leave kids or pets unattended in vehicles," Ramunni said.

Older people, infants and young children, and those with chronic health conditions such as lung or heart problems are especially at risk in high heat. Experts advise people to check on vulnerable neighbors and family members and help them get to cooling centers if necessary.

Europe has also been battered by extreme heat in the past week, as temperature records have been shattered from Denmark to Germany to Slovakia. Thousands of excess deaths have been reported.

Periods of extreme heat are happening more frequently, lasting longer, and becoming more intense because of human-caused global warming, according to climate scientists. 

By Saturday, Independence Day, the intense heat will lift somewhat with a high of around 93, but that will still be "one of the hottest July 4ths on record," Ramunni said.

The record is 97, set in 2010.

Last year 21 people died in New York City as a direct result of the heat, and nearly 500 New Yorkers die each year from causes exacerbated by heat, according to the city health department. New York State doesn’t keep a tally of heat-caused deaths, but 155 people visited emergency rooms in Nassau County for heat-related illness in 2024, according to the county health department.