As the worst of a heavy rainstorm moved northeast off Long Island, flooded roadways and patchy fog were expected to challenge drivers Thursday morning, the National Weather Service said.
The service's Upton office issued a flood watch until noon Thursday.
A dense fog advisory, mostly for the coastal areas in both counties, also is effective until noon, the service's Upton office said.
Meteorologist David Stark of the Upton office said patches of heavy fog are likely to limit visibility in some areas to a half-mile or less.
"That will be the big thing over the next several hours," Stark said of the fog. "Road conditions seem to be OK; some reports of minor flooding and ponding of roadways, but nothing much more significant."
Nassau County reported the heaviest of the rainfall, most of it overnight Wednesday into Thursday morning.
About 5.5 inches fell in Plainview, 5.1 in Merrick, 4.5 in Lido Beach and 4.4 in Bellmore, Stark said.
Northport and Farmingdale had the highest amounts in Suffolk, about 3.8 inches each, he said. The East End had far less: Orient Point was hit the hardest, with 2.0 inches.
Stark said most of the fog is expected to lift by noon, but it could linger near some coastal areas and even return there for some of the nighttime hours.
Once the fog lifts, Stark said partly cloudy skies could give way to sunshine and some afternoon temperatures as high as the mid to high 60s.
The service said heavy rain had ended across most of Long Island by about 5:30 a.m., but warned that "residual minor flooding of urban, low lying and poor drainage areas should continue early this morning."
The service urged motorists to avoid driving into areas where the water covers the roadway. "Turn around and find another route," the service's urban flood advisory said.
Because of flooding, Nassau County police issued a travel advisory for the south service road of the Long Island Expressway shortly after 5 a.m.
The service road was closed between Searingtown Road and Shelter Rock Road because of flooding, the advisory said, adding that motorists should not drive through standing water on roadways.
The state Department of Transportation also said in an alert at 8:30 a.m. the left lane of the eastbound Northern State Parkway -- in the same area, at Shelter Rock Road, Exit 27 -- was "blocked" because of flooding.