Scattered showers and thunderstorms in the region Saturday morning could persist through the evening hours, according to the National Weather Service in Upton.
Rain is likely to continue across Long Island through around noon, but the chance of additional storms is possible until midnight, said meteorologist Jay Engel.
Temperatures Saturday will top out in the lower 80s and drop to the low 70s overnight, Engel said.
The storms are also causing moderate delays in departures and arrivals at Kennedy, LaGuardia and Long Island MacArthur airports.
Sunday's forecast calls for more humid conditions and only a small chance of rain in western Nassau with temperatures expected to reach the mid 80s.
State officials on Friday issued an air quality health advisory for Long Island, the New York City metro region and the Lower Hudson Valley through 11 p.m. Sunday, citing high levels of ozone pollution.
Officials recommend limiting strenuous outdoor activities, minimizing automobile use and instead relying on public transportation.
The start of the workweek will bring little relief from the heat and humidity -- but could be one for the record books.
Monday's high temperature is projected to reach 91, potentially ending a record streak, beginning 2013, of 728 consecutive days in which the high temperature failed to reach 90 degrees at Long Island's official weather site, MacArthur Airport.
The Northeast Regional Climate Center at Cornell University has tracked the figures based on official records kept since 1984 by the National Weather Service.