A flash-flood watch is in effect in Nassau County and the western portion of Suffolk County from about midnight Sunday through 11 a.m. Monday, with expected rainfall of up to 2 inches.

The rain may be heaviest overnight and “would be tapering off around the time people are heading out the door” for work, but may still impact the morning commute, said meteorologist Faye Morrone of the National Weather Service in Upton.

After the watch is lifted, showers are likely to last into Monday evening with a 30 percent to 40 percent chance of rain.

Temperatures will “be on the cool side, especially compared to what we had this past week” with a low near 70 Sunday night and a high in the mid-70s Monday, Morrone said.

Peter Wichrowski, a meteorologist with the National Weather Service at Upton, said the normal high at Islip this time of year is 82 and the normal low is 67.

Clouds hang around into Tuesday morning ahead of gradual clearing throughout the afternoon. Tuesday’s high is expected to drop to 79 and the low to 66.

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Sunshine makes a comeback Wednesday, when the forecast calls for weather to be mixed with only a few clouds. High temperatures are forecast to be 79 and the low 65.

Sunny skies open the day Thursday, followed by increasing clouds, but the high will be 81 degrees and a low 68.

Mostly cloudy skies and scattered showers start the weekend Friday when another storm system moves through Long Island, and a high of 85 degrees is forecast along with an overnight low of 69.

With Rachelle Blidner