A family navigates their canoe along the Nissequogue River in...

A family navigates their canoe along the Nissequogue River in Kings Park on Saturday morning. Credit: Joseph Sperber

Sweltering temperatures and high humidity are expected to persist throughout Sunday on Long Island, forecasters said.

Highs are again forecast to reach into the 90s along northern parts of the Island, with widespread readings in the mid-80s, according to the National Weather Service. 

The weather service issued a heat advisory for northern Nassau County and northwest Suffolk County through Sunday, and an air quality alert is in effect until 11 p.m. Sunday for the majority of the tristate area. The heat advisory may have to be extended into other areas on Sunday, forecasters warned.

Thunderstorms are possible Sunday evening, but relief is on its way soon, forecasters said.

Weather service meteorologists say the heat may intensify on Sunday. Heat indexes are forecast to be over 90 degrees on nearly all of Long Island, according to the agency's Saturday morning briefing, reaching nearly 100 degrees in northern Nassau County. In western Suffolk County, forecasters say those values could reach the mid-90s.

Vulnerable groups, including seniors, infants and those with health problems, are at an increased risk of heat illness, the weather service said. 

For those heading to the beach to cool off, beware: There is a high risk of rip currents on Sunday.

The eastern half of the United States has endured elevated temperatures in the past week because of a heat dome — when slow-moving high pressure sinks to the surface and traps heat instead of allowing it to lift off the surface, triggering a heat wave. 

There will be a slight reprieve from scorching temperatures on Monday. The heat index to start the workweek will hover around the mid-80s, according to the weather service.

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