Great Diamond Island Weather Forecast

    • 53
    • 64

    Mostly Sunny

    • 56
    • 65

    Partly Sunny

    • 57
    • 68

    Slight Chance Rain Showers

    • 55
    • 65

    Mostly Sunny

    • 56
    • 67

    Mostly Sunny

    • 57
    • 68

    Mostly Sunny

    • 58
    • 68

    Partly Sunny

Today 12 Sep Coastal Cumberland

Sunny. Highs around 70. South Winds around 10 Mph.

Tonight 12 Sep Coastal Cumberland

Mostly clear. Lows in the upper 40s. Southwest Winds around 10 Mph in the Evening, becoming light and variable.

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Great Diamond Island Temperature Statistics

September Temperature

Portland, Portland International Jetport (5 miles)

  • Lowest 9 September, 2025

    46 °F

  • Average September

    62.6 °F

  • Highest 2 September, 2025

    78.1 °F

Climate (2020–Present)

Portland, Portland International Jetport (5 miles)

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  • Average Low 2020–2025

    40.5 °F

  • Average 2020–2025

    49 °F

  • Average High 2020–2025

    57.4 °F
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