National Oceanic and Atmospheric Administration National Weather Service United States Department of Commerce
Current conditions at

Islip, Long Island Mac Arthur Airport (KISP)

Lat: 40.79°NLon: 73.1°WElev: 98ft.

Partly Cloudy

75°F

24°C

Humidity 90%
Wind Speed Calm
Barometer 30.05 in (1017.4 mb)
Dewpoint 72°F (22°C)
Visibility 10.00 mi
Last update 15 Jul 3:56 am EDT
Extended Forecast for

Port Jefferson NY

  • Overnight

    Overnight: A 50 percent chance of showers and thunderstorms. Patchy fog. Otherwise, mostly cloudy, with a low around 73. Light southwest wind.

    Low: 73 °F

    Chance
    Showers and
    Patchy Fog

  • Tuesday

    Tuesday: A 30 percent chance of showers and thunderstorms, mainly before 11am. Patchy fog before 9am. Otherwise, cloudy through mid morning, then gradual clearing, with a high near 85. Calm wind becoming south 5 to 7 mph in the morning.

    High: 85 °F

    Chance
    Showers and
    Patchy Fog
    then Slight
    Chance
    T-storms

  • Tuesday Night

    Tuesday Night: Patchy fog after 11pm. Otherwise, partly cloudy, with a low around 73. South wind 5 to 7 mph becoming calm after midnight.

    Low: 73 °F

    Patchy Fog

  • Wednesday

    Wednesday: Patchy fog before 9am. Otherwise, mostly sunny, with a high near 88. Heat index values as high as 97. South wind 3 to 8 mph.

    High: 88 °F

    Patchy Fog
    then Mostly
    Sunny

  • Wednesday Night

    Wednesday Night: A 50 percent chance of showers and thunderstorms, mainly after 8pm. Mostly cloudy, with a low around 75. South wind 6 to 9 mph.

    Low: 75 °F

    Chance
    T-storms

  • Thursday

    Thursday: A chance of showers, with thunderstorms also possible after 2pm. Partly sunny, with a high near 89. Chance of precipitation is 30%.

    High: 89 °F

    Chance
    Showers then
    Chance
    T-storms

  • Thursday Night

    Thursday Night: A chance of thunderstorms before 8pm. Partly cloudy, with a low around 77. Chance of precipitation is 30%.

    Low: 77 °F

    Chance
    T-storms then
    Partly Cloudy

  • Friday

    Friday: A 30 percent chance of showers and thunderstorms after 2pm. Mostly sunny, with a high near 89.

    High: 89 °F

    Mostly Sunny
    then Chance
    T-storms

  • Friday Night

    Friday Night: A 30 percent chance of showers and thunderstorms before 8pm. Mostly cloudy, with a low around 71.

    Low: 71 °F

    Chance
    T-storms then
    Partly Cloudy

Detailed Forecast

Overnight
A 50 percent chance of showers and thunderstorms. Patchy fog. Otherwise, mostly cloudy, with a low around 73. Light southwest wind.
Tuesday
A 30 percent chance of showers and thunderstorms, mainly before 11am. Patchy fog before 9am. Otherwise, cloudy through mid morning, then gradual clearing, with a high near 85. Calm wind becoming south 5 to 7 mph in the morning.
Tuesday Night
Patchy fog after 11pm. Otherwise, partly cloudy, with a low around 73. South wind 5 to 7 mph becoming calm after midnight.
Wednesday
Patchy fog before 9am. Otherwise, mostly sunny, with a high near 88. Heat index values as high as 97. South wind 3 to 8 mph.
Wednesday Night
A 50 percent chance of showers and thunderstorms, mainly after 8pm. Mostly cloudy, with a low around 75. South wind 6 to 9 mph.
Thursday
A chance of showers, with thunderstorms also possible after 2pm. Partly sunny, with a high near 89. Chance of precipitation is 30%.
Thursday Night
A chance of thunderstorms before 8pm. Partly cloudy, with a low around 77. Chance of precipitation is 30%.
Friday
A 30 percent chance of showers and thunderstorms after 2pm. Mostly sunny, with a high near 89.
Friday Night
A 30 percent chance of showers and thunderstorms before 8pm. Mostly cloudy, with a low around 71.
Saturday
Sunny, with a high near 84.
Saturday Night
Mostly cloudy, with a low around 71.
Sunday
A 50 percent chance of showers. Partly sunny, with a high near 85.
Sunday Night
A 30 percent chance of showers. Mostly cloudy, with a low around 71.
Monday
A 30 percent chance of showers. Mostly sunny, with a high near 85.
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Forecast Area
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ABOUT THIS FORECAST

 
Point Forecast:
Port Jefferson NY
 40.95°N 73.05°W (Elev. 151 ft)
Last Update:
2:23 am EDT Jul 15, 2025
Forecast Valid:
4am EDT Jul 15, 2025-6pm EDT Jul 21, 2025
 
Forecast Discussion
 
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Additional Resources

Radar & Satellite Image

Link to Local Radar Data Link to Satellite Data

Hourly Weather Forecast

National Digital Forecast Database

National Digital Forecast Database Maximum Temperature Forecast

High Temperature

National Digital Forecast Database Weather Element Forecast

Chance of Precipitation