A “nice” day is shaping up for Long Island on Sunday, but things will take a turn for the worse on Monday when rain and possibly thunderstorms are predicted before things dry out for most of the rest of the week, forecasters say.

“It’s not going to be all that hot but there’ll be plenty of clear skies and sunshine,” News 12 Long Island meteorologist Bruce Avery said of Sunday.

Avery said the high in most areas will be 79 degrees and the low will be around 65.

Some of the warmest temperatures on the Island for Sunday will be found in Great Neck, Hewlett and Bethpage where the high will reach 81, while Jamesport and Sayville will see a high of 78, and Springs on the South Fork will have a high of just 77, Avery said.

“Overall Sunday will be a seasonably warm day — daytime-wise it will be very normal for this time of year,” said David Stark, a meteorologist with the National Weather Service in Upton. The normal high at Islip is 82 and the normal low 77, he said.

Stark said Sunday might seem a little cool for August, but that’s because the month is usually muggy whereas Sunday will have humidity levels of around 35 percent.

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“We’ve kind of reached our peak (in terms of the heat),” Stark said. “It stays in about the low 80s for the next several weeks,” he added.

Avery said that although Sunday will be “nice and sunny,” clouds will start to thicken by midnight. He predicted that perhaps some showers will form by dawn.

Heavy downpours are expected for earlier in the day Monday and another cycle is forecast for the afternoon, Avery said.

Stark said it will also become more humid on Monday and western Long Island will get rain arriving at between 10 a.m. and 11 a.m. The showers should reach eastern Long Island by early afternoon, he said. Rain accumulations could be from an inch to an inch-and-a-half, Stark said.

According to News 12, a high of 76 is expected for Monday and a low of 66. The sun returns on Tuesday when the high will be 79 and the low 64.

On Wednesday, look for mostly sunny skies and for the mercury to climb to a high of 81. The low will be 65.

A mix of sun and clouds is ahead for Thursday when the high will drop only slightly to 80 degrees but the low will be a warmer 67.

On Friday, Stark said, it will be partly sunny but pop-up showers are possible when the high will be 79 and the low 65.