April is a time of year when sea breezes start playing a greater role in Long Island’s weather.

Sea breezes can occur just about any time of year, but they take on new meaning with springtime and its warming temperatures, forecasters say.

That’s when they can be stronger than at other times and can reach farther inland, said Tim Morrin, a National Weather Service meteorologist in Upton.

What they do — and why they matter

When winds shift and start coming off the cooler waters, we can start seeing a cool-down over land, with wide ranges in temperatures and a difference of as much as 10 to 15 degrees between areas along the south and north shores.

This shift in wind direction, which may come about suddenly, “can be quite refreshing during spells of hot weather,” said Bill Korbel, a News 12 Long Island meteorologist. On the other hand, they might also raise humidity levels, which can negate those cooler temperatures.

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Some issues can also arise:

  • As these breezes head inland, they “can sometimes trigger a thunderstorm” as “cool, ocean air meets the opposing air flow,” creating “additional lift in the atmosphere.”
  • And boaters, enjoying calm winds and waters in the morning, can be confronted in the afternoon with “20 to 25 mph winds,” which mean “rougher seas on the ocean and waves on South Shore bays,” Korbel said.
  • Pilots, particularly those landing at or taking off from airports with no control tower, have to be alert for any wind-direction shift, which can come about “very quickly . . . sometimes by 180 degrees,” he said. That’s why they’ll want to check airports’ large wind vanes. Another thing to watch out for is turbulence and wind shear, Korbel said, which come along as sea breezes arrive.

Why now — the setup

The breezes have more punch now, as spring and summer bring the biggest differences in temperatures between land and sea, with energy from the sun warming up the land faster than it warms up water.

The land warms up and then reflects that heat into the air, which earlier this week reached 60, 70, even 80 degrees. So, by afternoon, air above land can warm up pretty well.

The ocean doesn’t warm up nearly as quickly. That’s because “solar radiation distributes its energy much deeper in water, so the water can’t warm as much,” Morrin said.

Hence, the air over it stays cooler.

How sea breezes form

Because the warm air over land “is less dense than cool air, it rises, as it is lighter than the cooler air above it,” Korbel said.

The cooler air over water moves in to replace that rising warmer air, leading the surface wind “to switch direction and blow from the water.”

“As the afternoon wears on, the sea breeze normally strengthens and moves further and further inland,” he said, and “its cooling relief can sometimes be felt many miles inland.”

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Why don’t they happen every spring day?

For one thing, sea breezes are more likely on days that see a wider gap between air temperatures over land and water, said Faye Barthold, a weather service meteorologist in Upton.

Also, if strong winds from the north are already blowing, Korbel said, they “keep the sea breeze from developing.”