With widespread and sometimes heavy rain forecast to dump 2 to 3 inches from late Tuesday night possibly into Wednesday afternoon, a flash flood watch is in effect for Long Island for that time frame, the National Weather Service said.
Rainfall could also be locally higher, said Joe Pollina, weather service meteorologist based in Upton. At its heaviest, the rainfall rate could briefly amount to 1 to 2 inches an hour, he said.
"Rainfall of this intensity and magnitude" could lead to "significant urban and poor drainage flooding," affecting the Wednesday morning commute and possibly worsening coastal flooding in low-lying areas, the service said.
Already, thanks to the combination of onshore winds and high tides, a coastal flood advisory is in effect Monday from 7 to 10 p.m. -- which changed from 8 to 11 p.m. -- for southern Nassau's bays, meaning "the most vulnerable" basements and/or shore roads could be flooded, with most roads remaining passable, the National Weather Service said. Tides are expected to be 6 inches to 1 foot above normal.
To the north, minor coastal flooding of "the lowest lying locations" is also expected with Monday night's high tide at around midnight for areas along the Long Island Sound, west of the Sound Beach-Rocky Point-Shoreham area, said Tim Morrin, weather service meteorologist in Upton. The high tide there is expected to be 6 inches above normal.
In conjunction with the heavy rainfall, more minor coastal flooding is likely with Tuesday's high tides, especially at night, the service said.