Rain and increasingly mild temperatures will rule Friday and Saturday, and Sunday should be sunny, the National Weather Service in Islip said.
The chances of showers are 50/50 after noon on Friday, and the high will reach an abnormally warm 50 degrees.
With as much as two inches of rain expected to fall Friday night — accompanied by fog — up to half a foot of flooding is possible everywhere in Suffolk except for the northwest part of the county, and as much as 1½ feet of water could wash into southern Nassau, the weather service said.
In Suffolk, flooding is possible during high tides from Saturday morning to Sunday afternoon. In Nassau, the risks run from 7 a.m. to noon on Saturday.
Saturday’s high could hit 57 degrees. Were the thermometer to fall below freezing, those two inches of rain would work out to around two feet of snow, experts say.
Sunday should offer mostly clear skies, and once again, a clement temperature of 46 degrees. Stiff breezes, however, could offset that mild thermometer reading: gusts could hit 37 mph, the weather service said.
Monday should be at least partly sunny and colder, with a high in the upper 30s.
That brief dry spell ends on Monday night, when the weather service predicts a triple threat of rain, snow and sleet, which likely will transform to rain after midnight.
The rain probably will not stop until around noon on Tuesday. The high is expected to be around 46 degrees.
The sun should return on Wednesday, when the high will likely be around 37 degrees, the forecasters said.