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.

Mostly Cloudy

82°F

28°C

Humidity 67%
Wind Speed N 3 mph
Barometer 29.88 in (1011.6 mb)
Dewpoint 70°F (21°C)
Visibility 10.00 mi
Heat Index86°F (30°C)
Last update 18 Aug 11:56 am EDT
Extended Forecast for

Port Jefferson NYSimilar City Names

  • This Afternoon

    This Afternoon: A 20 percent chance of showers after 2pm. Partly sunny, with a high near 83. Light west wind.

    High: 83 °F

    Slight Chance
    Showers

  • Tonight

    Tonight: A 20 percent chance of showers before 11pm. Partly cloudy, with a low around 69. Light and variable wind.

    Low: 69 °F

    Slight Chance
    Showers then
    Partly Cloudy

  • Wednesday

    Wednesday: Sunny, with a high near 85. Light and variable wind becoming west around 6 mph in the afternoon.

    High: 85 °F

    Sunny

  • Wednesday Night

    Wednesday Night: Partly cloudy, with a low around 71. South wind 5 to 8 mph becoming west after midnight.

    Low: 71 °F

    Partly Cloudy

  • Thursday

    Thursday: A 40 percent chance of showers and thunderstorms after 2pm. Mostly sunny, with a high near 81. North wind around 5 mph becoming west in the afternoon.

    High: 81 °F

    Mostly Sunny
    then Chance
    Showers

  • Thursday Night

    Thursday Night: A 50 percent chance of showers. Mostly cloudy, with a low around 67.

    Low: 67 °F

    Chance
    Showers

  • Friday

    Friday: Partly sunny, with a high near 80.

    High: 80 °F

    Partly Sunny

  • Friday Night

    Friday Night: A 30 percent chance of showers after 2am. Mostly cloudy, with a low around 68.

    Low: 68 °F

    Mostly Cloudy
    then Chance
    Showers

  • Saturday

    Saturday: A 50 percent chance of showers. Partly sunny, with a high near 77.

    High: 77 °F

    Chance
    Showers

Detailed Forecast

This Afternoon
A 20 percent chance of showers after 2pm. Partly sunny, with a high near 83. Light west wind.
Tonight
A 20 percent chance of showers before 11pm. Partly cloudy, with a low around 69. Light and variable wind.
Wednesday
Sunny, with a high near 85. Light and variable wind becoming west around 6 mph in the afternoon.
Wednesday Night
Partly cloudy, with a low around 71. South wind 5 to 8 mph becoming west after midnight.
Thursday
A 40 percent chance of showers and thunderstorms after 2pm. Mostly sunny, with a high near 81. North wind around 5 mph becoming west in the afternoon.
Thursday Night
A 50 percent chance of showers. Mostly cloudy, with a low around 67.
Friday
Partly sunny, with a high near 80.
Friday Night
A 30 percent chance of showers after 2am. Mostly cloudy, with a low around 68.
Saturday
A 50 percent chance of showers. Partly sunny, with a high near 77.
Saturday Night
Showers likely, mainly before 2am. Mostly cloudy, with a low around 68. Chance of precipitation is 60%.
Sunday
A 50 percent chance of showers. Mostly cloudy, with a high near 79.
Sunday Night
A 30 percent chance of showers. Mostly cloudy, with a low around 67.
Monday
Sunny, with a high near 79.
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Forecast Area
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ABOUT THIS FORECAST

 
Point Forecast:
Port Jefferson NYSimilar City Names
 40.95°N 73.05°W (Elev. 151 ft)
Last Update:
5:37 am EDT Aug 18, 2026
Forecast Valid:
12pm EDT Aug 18, 2026-6pm EDT Aug 24, 2026
 
Forecast Discussion
 
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Additional Resources

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High Temperature

National Digital Forecast Database Weather Element Forecast

Chance of Precipitation