The rain, at its heaviest just before 6 a.m., turned the morning commute into a nightmare. The Long Island Railroad reported delays of more than half an hour, and sections of the Long Island Expressway and other major highways were closed because of flooding.
By 8 a.m., 13 inches of rain had been recorded in Islip on the southern shore of Suffolk County, the National Weather Service said. That was almost twice the previous daily record of 6.7 inches.
Police had to rescue drivers on some roads after flash flooding left them stuck in their vehicles.
Tim Morin, a forecaster with the NWS, said the agency had been tracking the storm, which moved across from the Jersey Shore, and had issued a flash flood warning. But he said the amount of rain was unexpected.
"There's no information that any meteorologist would have that you would anticipate that excessive, off-the-chart type of amounts," Morrin told the Long Island Press.