Long Islanders can expect heavy rain and potential flash flooding Thursday as a cold front from the west interacts with tropical moisture from the south, forecasters said.
Associated with Tropical Storm Michael, the moisture, “surging northward from eastern North Carolina and Virginia, will move up into the area this afternoon and tonight,” the National Weather Service said in a flash flood watch. The watch is in effect for the entire metropolitan region. On Long Island, the watch lasts from noon through late Thursday.
The storm itself will stay to the south, moving off the coast and into the mid-Atlantic later in the day, according to the National Hurricane Center track.
Look for showers and a few thunderstorms starting late morning to early afternoon, said Joe Pollina, a National Weather Service meteorologist in Upton.
Long Island is looking at 1.5 to 2 inches of rain Thursday, with 2 to 4 possible in some spots, the watch said. Any heavy precipitation falling within a one- to three-hour time frame could result in flash flooding.
With the Island already having had an abundance of recent precipitation, “the ground is still rather moist and with up to 2 inches of rain or even a bit more possible, there will be some local flooding to contend with,” said News 12 Long Island meteorologist Bill Korbel.
Isolated minor coastal flooding is expected with the morning to early afternoon high tide cycle, particularly for the most vulnerable spots along the South Shore bays of Nassau County.
The weather service issued a small craft advisory from noon to 6 a.m. Friday for seas of 7 to 11 feet and a gale warning until 6 p.m. Friday, both for waters off the South Shore. There is also a small craft advisory for the Long Island Sound.
Thursday should be the last day with highs in the mid-70s for the near future as the cold front moves in. Thursday’s low will be near 61.
“We have big changes coming our way,” said News 12 Long Island meteorologist Rich Hoffman. “Go find those jackets, because you’re going to need them by the weekend.”
Showers continue into Friday morning, with cloudy skies gradually becoming mostly sunny. The day also sees an increase in winds from the northwest, with a few gusts of 35 to 40 mph possible. Highs will be in the mid-60s with lows dropping all the way to the low 40s.
Saturday and Sunday will have highs near 60 and lows near 50. “Overall most of the weekend looks good for outdoor fall events — just watching wet weather Saturday morning,” Hoffman said.
This will be the first time this month that daily highs dip to below normal, which at this point is 64 degrees at Long Island MacArthur Airport in Ronkonkoma. As of day-end Wednesday, the month so far was averaging 10.2 degrees above normal.