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

70°F

21°C

Humidity 82%
Wind Speed NE 12 mph
Barometer 30.04 in (1017.3 mb)
Dewpoint 64°F (18°C)
Visibility 10.00 mi
Last update 21 Aug 6:56 pm EDT
Extended Forecast for

Port Jefferson NY

  • Tonight

    Tonight: Mostly cloudy, with a low around 65. Northeast wind 6 to 9 mph.

    Low: 65 °F

    Mostly Cloudy

  • Saturday

    Saturday: A 30 percent chance of showers, mainly after 5pm. Mostly cloudy, with a high near 74. Northeast wind 5 to 8 mph.

    High: 74 °F

    Mostly Cloudy
    then Chance
    Showers

  • Saturday Night

    Saturday Night: A 50 percent chance of showers and thunderstorms, mainly after 11pm. Mostly cloudy, with a low around 66. East wind around 5 mph.

    Low: 66 °F

    Chance
    Showers

  • Sunday

    Sunday: A 50 percent chance of showers and thunderstorms. Partly sunny, with a high near 79. East wind 5 to 7 mph becoming south in the afternoon.

    High: 79 °F

    Chance
    Showers

  • Sunday Night

    Sunday Night: Partly cloudy, with a low around 67. West wind 6 to 8 mph.

    Low: 67 °F

    Partly Cloudy

  • Monday

    Monday: Sunny, with a high near 79.

    High: 79 °F

    Sunny

  • Monday Night

    Monday Night: Mostly clear, with a low around 65.

    Low: 65 °F

    Mostly Clear

  • Tuesday

    Tuesday: Sunny, with a high near 77.

    High: 77 °F

    Sunny

  • Tuesday Night

    Tuesday Night: Mostly clear, with a low around 66.

    Low: 66 °F

    Mostly Clear

Detailed Forecast

Tonight
Mostly cloudy, with a low around 65. Northeast wind 6 to 9 mph.
Saturday
A 30 percent chance of showers, mainly after 5pm. Mostly cloudy, with a high near 74. Northeast wind 5 to 8 mph.
Saturday Night
A 50 percent chance of showers and thunderstorms, mainly after 11pm. Mostly cloudy, with a low around 66. East wind around 5 mph.
Sunday
A 50 percent chance of showers and thunderstorms. Partly sunny, with a high near 79. East wind 5 to 7 mph becoming south in the afternoon.
Sunday Night
Partly cloudy, with a low around 67. West wind 6 to 8 mph.
Monday
Sunny, with a high near 79.
Monday Night
Mostly clear, with a low around 65.
Tuesday
Sunny, with a high near 77.
Tuesday Night
Mostly clear, with a low around 66.
Wednesday
Sunny, with a high near 79.
Wednesday Night
A 30 percent chance of showers. Partly cloudy, with a low around 68.
Thursday
A 40 percent chance of showers. Partly sunny, with a high near 79.
Thursday Night
A 40 percent chance of showers. Mostly cloudy, with a low around 69.
Friday
Mostly sunny, with a high near 80.
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Forecast Area
Tiles ©ESRI

ABOUT THIS FORECAST

 
Point Forecast:
Port Jefferson NY
 40.95°N 73.05°W (Elev. 151 ft)
Last Update:
2:49 pm EDT Aug 21, 2026
Forecast Valid:
7pm EDT Aug 21, 2026-6pm EDT Aug 28, 2026
 
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