The occasional sunshine that bathed Long Island early in the week will be replaced by scattered showers and thunderstorms Thursday, with the heaviest downpours expected in western areas, forecasters said.

The National Weather Service has issued a flash flood watch -- short of a warning -- for Thursday for New York City and Nassau County, but not for Suffolk County.

Dense fog rolled in late Wednesday, and forecasters said Thursday's rain could be heavy at times. Most areas should get a half-inch to 11/2 inches of rain, but there was the possibility of as much as 3 inches in the watch area.

"What you will see will be . . . low cloud and fog in the morning and then a cold front and moisture moves through in the afternoon," meteorologist David Wally of the National Weather Service in Upton said.

"There is the potential there for some heavy rain at times," he said, adding the heaviest was expected north and west of the city. The weekend forecast was for a mix of sun and clouds.

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