Heat dome over Long Island: What to know about the upcoming heat wave

Long Island is bracing for its first major heat wave since 2023, starting Sunday and lasting into Wednesday, as the result of a heat dome that will cover the region. 

The National Weather Service on Saturday issued a heat advisory for between noon and 8 p.m. Sunday for Nassau and western Suffolk counties. At noon on Monday, an extreme heat watch takes effect and continues through 8 p.m. Tuesday, according to the weather service.

Elevated ozone levels also led to an air quality health advisory for Long Island Sunday between 11 a.m. and 11 p.m. The area is also at a "marginal risk" of a thunderstorm Sunday, NWS said.

Here is a primer from Newsday meteorologist Rich Von Ohlen about what to expect.

What is a heat dome?

Sometimes called “the ring of fire,” it’s a large, enclosed zone of dry air where the jet stream (upper wind flow) goes well north into Canada, then wraps back around to the south and east, creating a big rotating circle of what becomes hot air. It’s most prevalent during the height of summer – June, July and August.

What causes it to get so hot?

The heat dome does two things: First, it allows for maximum sunlight and dry air, allowing the sun to bake the Earth. It feels like a hot desert. Second, it typically aligns in a way that the surface winds become more westerly, which brings compressed, optimum heating conditions. When this occurs, the ocean waters do not have as much of an influence in cooling most areas as they typically would.

How hot can it get in the dome?

If the orientation and time of the year are right, surface temperatures can rise well above 95 degrees, often hitting 100-105 in the core of the heat dome. This does not include the heat index, which takes into account the level of humidity. On days that are extra humid, and with a heat dome in place, those real-feel temperatures can reach between 105 and 115 degrees, which is considered dangerous.

Typically, excessive heat watches, warnings or heat advisories will be issued by the National Weather Service and others before this extreme heat, making everyone aware of the likely hazardous condition heading our way.

How long is this heat dome expected to last?

The forecast has been consistent with three days – Monday, Tuesday and Wednesday – where we are within the zone of the heat dome across the Eastern states. If official recording stations hit 90 degrees for three days in a row, it's officially considered a heat wave. Long Island, according to measurements at Long Island MacArthur Airport in Ronkonkoma, did not see an official heat wave in 2024. The last heat wave at MacArthur was Sept. 6-8, 2023.

Newsday's Joe Werkmeister contributed to this story.