Lori Shook, left, and Paul Zanette, of Fishkill, visit Norman E. Klipp...

Lori Shook, left, and Paul Zanette, of Fishkill, visit Norman E. Klipp Marine Park in Greenport on Thursday. Credit: Morgan Campbell

Long Island, unlike much of the United States, was not expected to fall under a heat advisory Friday, the first full day of summer. But it will be scorching hot, with hotter coming, forecasters said. 

A National Weather Service heat index map showed the North Shore would bear the brunt of the heat and humidity Friday, with index values of 92 degrees in Syosset and 91 in Stony Brook. Slightly more comfortable conditions were predicted for the South Shore and East End, with a high of 86 for Islip and 82 in Montauk. The hottest temperatures were forecast for noon to 8 p.m.

The actual high air temperature in Syosset is expected to be about 89 degrees on Friday.

The heat index, or apparent temperature, is what the temperature feels like to the human body when relative humidity is combined with the air temperature. Prolonged exposure in index values between 80-90 degrees may cause fatigue. Prolonged exposure in index values of 90-103 degrees may cause heat stroke, heat cramps or heat exhaustion.

An air quality warning will be in effect Friday from 11 a.m. to 11 p.m. because ground-level ozone, a pollutant, is expected to reach or exceed unhealthy standards. 

No real relief was expected for the North Shore on Saturday, when the heat index was again predicted to hit the 90s. On Sunday, almost all Long Island and New York City will swelter, forecasters said. The index predictions for that day are 97 degrees in Syosset, 88 in Islip and 92 in New York City. 

Potential cloud cover and rain Friday and Saturday could yield lower heat indexes, but that effect was expected mainly for areas north of New York City, according to the weather service. 

Friday could bring the hottest temperatures of the year so far for the Island, said David Stark, a meteorologist at the National Weather Service's station in Upton. But temperatures will be moderated by the relatively cool waters of the Atlantic Ocean.

Ocean water is still as cool as 50 or 60 degrees, he said, and winds blowing off the ocean are “helping to counter some of the heat, keeping us more muted.” 

By Thursday night, weather service forecasters said the heat wave had probably peaked in the eastern Great Lakes and New England, with higher temperatures expected in the Ohio Valley and Mid-Atlantic on Friday into the weekend. Widespread daily record high temperatures were likely, forecasters said. 

On Long Island this week, those who could luxuriated in air conditioning or headed for the beaches. On Wednesday, which was both hot and a federal holiday, Juneteenth, more than 100,000 people visited Jones Beach, Robert Moses State Park and Sunken Meadow State Park, said George Gorman, Long Island regional director of the New York State Office of Parks, Recreation and Historic Preservation. Parking fees were waived and visitors came within 100 vehicles of filling 5,500 parking stalls at Robert Moses. 

Robert Moses drew visitors again Thursday. 

"At home, it's really hot, but here by the ocean, the breeze makes it really nice," said Sharon Rutledge, of Islip.

"It's been beautiful by the water," said her friend, Libby Passamano, also of Islip.

Several Long Island towns have opened air-conditioned cooling centers or are extending pool and beach hours to help residents cope with the heat this week. 

In North Hempstead, where Town Supervisor Jennifer DeSena asked residents to "check in on vulnerable neighbors, especially our seniors," cooling centers were open daily at two community centers and a park, and pools remained open until 9 p.m. 

Hempstead Town offered respite at eight senior centers, kept its beaches open until 7 p.m. and its pools until 8 p.m., an hour or more past the usual closing time. In an interview, Town Supervisor Donald X. Clavin Jr. said the beaches and pools drew many more residents than the cooling centers.

"A lot of families with kids are taking advantage and we expect that same level of activity at a minimum through [Friday] evening," he said. 

Nassau County opened cooling centers at administration buildings in Hicksville, Wantagh and Uniondale, according to the state Department of Health, though a county spokesman said in an email they were sparsely attended. Anyone hoping to use them was asked to call before visiting to confirm they were open. The Mitchel Field Complex Administration Building was open 24 hours a day. The Health Department did not list any cooling centers for Suffolk.

If Long Island is uncomfortable, the heat is worse — and potentially dangerous — in other parts of the metropolitan region. Friday and over the weekend, the heat index is expected to top 100 degrees in parts of New Jersey, the Lower Hudson Valley and Connecticut. Heat advisories imposed Thursday are in place again for some of those areas and may be extended through the weekend. The weather service has warned of an “increased risk of heat-related illness for vulnerable populations” for those areas.

The air quality alert was first issued Thursday and repeated for Friday. Ground-level ozone is created when pollutants from cars, power plants and other sources react chemically under sunlight. Friday's predicted air quality index was 115 for Long Island and New York City. That level, labeled orange on the federal Environmental Protection Agency's color-coded system, is described as "unhealthy for sensitive groups."

The EPA recommends people with lung diseases such as asthma, as well as children and teens, older adults, and people who are routinely active outdoors for six or more hours a day, choose less strenuous activities or reduce outdoor activity time. 

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