Long Islanders should get those outdoor plans in by Saturday, because it's likely to be a wet Sunday, the National Weather Service said.
While Friday will be a keeper, by Sunday the chance of showers and thunderstorms ranges from 50 percent to 70 percent, the service's Upton office said.
Daily highs Friday could reach 80 in some parts of northern Nassau County, News 12 Long Island meteorologist Rich Hoffman said.
"Dry and beautiful weather today with temperatures above normal," Hoffman said of Friday's forecast.
Hoffman said conditions change gradually, starting with some fog Saturday morning, perhaps dense on the South Shore, after overnight lows from the high 50s to low 60s.
Most of Saturday afternoon is sunny, "with a small chance of a late day shower or storm."
High temperatures from the low to upper 70s are expected with southwest winds from 10 to 15 mph.
A cold front approaching from the northwest brings in the precipitation, possibly starting as early as Saturday night.
Chances for precipitation increase as the front moves west to east. Most models indicate showers and thunderstorms from Sunday morning into the afternoon hours, with "abundant cloud cover," the service said.
Hoffman said the "much-needed" rain will stretch into Monday, which calls for mostly cloudy skies and breezy, cool conditions.
From late Saturday to Monday, Hoffman said as much as three-quarters of an inch to 1 1/2 inches of rain could fall across Nassau and Suffolk counties.