Great Diamond Island Weather Forecast

    • 50
    • 66

    Slight Chance Rain Showers

    • 56
    • 61

    Mostly Sunny

    • 59
    • 68

    Partly Sunny

    • 59
    • 65

    Chance Rain Showers

    • 55
    • 69

    Partly Sunny

    • 55
    • 64

    Chance Rain Showers

Today 14 Sep Coastal Cumberland

Partly sunny with a slight chance of Showers in the Morning, then sunny in the afternoon. Highs in the lower 70s. Northwest Winds 15 to 20 Mph with Gusts up to 30 Mph. Chance of rain 20 percent.

Tonight 14 Sep Coastal Cumberland

Cloudy with a 20 percent chance of Showers. Areas of fog. Lows around 60. Light and variable Winds.

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Great Diamond Island Temperature Statistics

September Temperature

Portland, Portland International Jetport (5 miles)

  • Lowest 7 September, 2026

    50.6 °F

  • Average September

    66.3 °F

  • Highest 10 September, 2026

    85.6 °F

Climate (2021–2026)

Portland, Portland International Jetport (5 miles)

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  • Average Low 2021–2026

    40 °F

  • Average 2021–2026

    48.7 °F

  • Average High 2021–2026

    57.3 °F
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