Thursday will offer all the delights of a fine late-spring day, with sunny skies and a high of 78 degrees predicted.

And the top temperature Long Islanders can expect through next Wednesday is just two degrees warmer, the National Weather Service said.

There is a 30% chance of afternoon showers on Sunday, which could last into Monday morning. Yet that is the sole damp patch the weather service predicted for the next seven days.

A high pressure system is building into the region, the weather service said, while what it calls a "back door cold front" is delivering drier air.

Dew points, a measure of how much moisture the air can hold before vapors arise, are slipping into the 50s, quite a contrast from the recent heat-intensifying humidity.

"A light northeast wind will allow for the airmass to feel much more comfortable than in recent days," the weather service said.

High pressure systems can produce clear skies as air falls to earth, cooling and drying. Low pressure systems, like the one that may dampen Sunday afternoon, can cause showers as their rising air warms, allowing rain drops to develop.

Cooler temperatures, then rain

For Thursday night, the weather service said, "Low temperatures will be in the low to middle 50s for much of the area with coastal and urban locations dropping into the upper 50s and low 60s."

Friday and Saturday will be mostly sunny, but slightly cooler, with daytime highs of 72 and 74 degrees, respectively.

Sunday should be mostly sunny as well, at least until around 3 p.m., when showers may arrive, the weather service said. The shifting systems make it difficult to precisely time any downpours.

"High pressure moves offshore by Sunday morning, as a surface low pressure brings a warm front through the area on Sunday morning followed by a cold front later in the day," the weather service said.

And then, the weather service said, look for "a bit of a warming trend for Sunday into Monday, with afternoon temperatures in the low to mid-80s for New York City, northeast New Jersey and the lower Hudson Valley, and in the upper 70s to lower 80s elsewhere."

Monday morning might begin with "scattered showers," said the weather service, which put the odds of rain at 30% before 9 a.m. And Monday is when the daytime high should climb to 80 degrees.

Tuesday and Wednesday should be mostly sunny, with daytime highs in the upper 70s.

"High pressure builds west from the Ohio Valley by Wednesday for the remainder of the period," the weather service explained.

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