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

40°F

4°C

Humidity 100%
Wind Speed W 5 mph
Barometer 29.74 in (1007.0 mb)
Dewpoint 40°F (4°C)
Visibility 7.00 mi
Wind Chill36°F (2°C)
Last update 21 Mar 3:56 am EDT
Extended Forecast for

Port Jefferson NY

  • Today

    Today: Mostly cloudy, then gradually becoming sunny, with a high near 49. Northwest wind 8 to 11 mph.

    High: 49 °F

    Decreasing
    Clouds

  • Tonight

    Tonight: Increasing clouds, with a low around 41. North wind around 6 mph becoming southeast after midnight.

    Low: 41 °F

    Increasing
    Clouds

  • Sunday

    Sunday: A 30 percent chance of rain after 2pm. Mostly cloudy, with a high near 52. Southwest wind 10 to 13 mph.

    High: 52 °F

    Mostly Cloudy
    then Chance
    Rain

  • Sunday Night

    Sunday Night: Rain, mainly after 8pm. Low around 40. Southwest wind 9 to 11 mph becoming north after midnight. Chance of precipitation is 80%. New precipitation amounts between a quarter and half of an inch possible.

    Low: 40 °F

    Rain

  • Monday

    Monday: A 40 percent chance of rain before 2pm. Cloudy, then gradually becoming mostly sunny, with a steady temperature around 41. North wind 14 to 16 mph.

    High: 41 °F

    Chance Rain

  • Monday Night

    Monday Night: Mostly clear, with a low around 33.

    Low: 33 °F

    Mostly Clear

  • Tuesday

    Tuesday: Sunny, with a high near 43.

    High: 43 °F

    Sunny

  • Tuesday Night

    Tuesday Night: Mostly cloudy, with a low around 36.

    Low: 36 °F

    Mostly Cloudy

  • Wednesday

    Wednesday: Partly sunny, with a high near 48.

    High: 48 °F

    Partly Sunny

Detailed Forecast

Today
Mostly cloudy, then gradually becoming sunny, with a high near 49. Northwest wind 8 to 11 mph.
Tonight
Increasing clouds, with a low around 41. North wind around 6 mph becoming southeast after midnight.
Sunday
A 30 percent chance of rain after 2pm. Mostly cloudy, with a high near 52. Southwest wind 10 to 13 mph.
Sunday Night
Rain, mainly after 8pm. Low around 40. Southwest wind 9 to 11 mph becoming north after midnight. Chance of precipitation is 80%. New precipitation amounts between a quarter and half of an inch possible.
Monday
A 40 percent chance of rain before 2pm. Cloudy, then gradually becoming mostly sunny, with a steady temperature around 41. North wind 14 to 16 mph.
Monday Night
Mostly clear, with a low around 33.
Tuesday
Sunny, with a high near 43.
Tuesday Night
Mostly cloudy, with a low around 36.
Wednesday
Partly sunny, with a high near 48.
Wednesday Night
Mostly cloudy, with a low around 37.
Thursday
Mostly cloudy, with a high near 47.
Thursday Night
Rain likely. Mostly cloudy, with a low around 40. Chance of precipitation is 60%.
Friday
Rain likely. Partly sunny, with a high near 47. Chance of precipitation is 60%.
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Forecast Area
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ABOUT THIS FORECAST

 
Point Forecast:
Port Jefferson NY
 40.96°N 73.08°W (Elev. 3 ft)
Last Update:
2:34 am EDT Mar 21, 2026
Forecast Valid:
4am EDT Mar 21, 2026-6pm EDT Mar 27, 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