Portland
Maine, USA
Long-term weather forecast
Long-term weather forecast

September weather forecast and climate
Portland, ME

Dusk view of the lit skyscrapers of the Portland city in Maine
Dusk view of the lit skyscrapers of the Portland city in Maine
September, the first month of the autumn, in Portland, is still a pleasant month, with average temperature fluctuating between 70°F (21.1°C) and 50.4°F (10.2°C).

Temperature

In Portland, the average high-temperature marginally drops, from a warm 77.7°F (25.4°C) in August, to a pleasant 70°F (21.1°C). The average low-temperature, is 50.4°F (10.2°C).

Humidity

September is the most humid month in Portland, Maine, with an average relative humidity of 76.7%.

Rainfall

In Portland, during September, the rain falls for 9.2 days and regularly aggregates up to 3.7" (93.7mm) of precipitation. In Portland, during the entire year, the rain falls for 130.9 days and collects up to 47.3" (1200.3mm) of precipitation.

Snowfall

Throughout the year, 61.9" (1572.3mm) of snow is accumulated.

Ocean temperature

In September, the average ocean temperature in Portland is 60.4°F (15.8°C).
Note: For swimming, a surface water temperature of 60.4°F (15.8°C) is not enjoyable for the majority. It is not considered safe, as controlling breathing becomes progressively more difficult as water temperature decreases below 69.8°F (21°C).

Daylight

The average length of the day in Portland is 12.5h.

Sunshine

In September, the average sunshine is 7.6h.

UV index

In September, the average daily maximum UV index in Portland is 5. A UV Index reading of 3 to 5 represents a moderate threat to health from unprotected exposure to the Sun's UV rays for average individuals.
Note: The daily maximum UV index of 5 in September interpret into the following advice:
Take precautions - Protection against sun damage is advised. The solar radiation is most powerful near the mid-day, so the exposure to the direct Sun should be reduced accordingly. Sun-protective clothing, a long-sleeved shirt and pants, a wide-brimmed hat, and UVA and UVB-blocking sunglasses are particularly helpful in blocking UV radiation's harmful effects.

What is the temperature in September in Portland?

The average high-temperature, in September, in Portland, Maine, is 70°F (21.1°C), while the average low-temperature is 50.4°F (10.2°C).

What is the most humid month in Portland?

September is the most humid month in Portland, with an average relative humidity of 76.7%.

What is the average humidity in September in Portland?

In Portland, Maine, the average relative humidity in September is 76.7%.

How many days does it rain in September in Portland?

In Portland, Maine, in September, during 9.2 rainfall days, 3.7" (93.7mm) of precipitation is typically accumulated.

What is the ocean temperature in September in Portland?

In Portland, the average seawater temperature in September is 60.4°F (15.8°C). For swimming, a surface water temperature of 60.4°F (15.8°C) is not enjoyable for the majority. It is not considered safe, as controlling breathing becomes progressively more difficult as water temperature decreases below 69.8°F (21°C).

What is the average length of the day in September in Portland?

The average length of the day in September is 12.5h.

How many hours of sunshine does Portland have in September?

The average sunshine in September in Portland is 7.6h.

What is the UV index reading in September in Portland?

In Portland, the average daily maximum UV index in September is 5. A UV Index value of 3 to 5 symbolizes a moderate health threat from unprotected exposure to the UV radiation.
Average temperature in September - Portland, ME
  • Average high temperature in September: 70°F

The warmest month (with the highest average high temperature) is July (78.8°F).
The month with the lowest average high temperature is January (31.2°F).

  • Average low temperature in September: 50.3°F

The month with the highest average low temperature is July (59.4°F).
The coldest month (with the lowest average low temperature) is January (13.4°F).

Average humidity in September - Portland, ME
  • Average humidity in September: 76.7%

The month with the highest relative humidity is September (76.7%).
The month with the lowest relative humidity is February (65.2%).

Average rainfall in September - Portland, ME
  • Average rainfall in September: 3.7"

Wettest months (with the highest rainfall) are October and November (4.9").
The driest month (with the lowest rainfall) is August (3.1").

Average rainfall days in September - Portland, ME
  • Average rainfall days in September: 9.2 days

The month with the highest number of rainy days is May (12.6 days).
The month with the lowest number of rainy days is September (9.2 days).

Average snowfall in September - Portland, ME
  • Average snowfall in September: 0"

The month with the highest snowfall is January (19.2").
Months with the lowest snowfall are May, June, July, August, September and October (0").

Average snowfall days in September - Portland, ME
  • Average snowfall days in September: 0 days

The month with the highest number of snowfall days is January (7.9 days).
Months with the lowest number of snowfall days are May, June, July, August, September and October (0 days).

Average sea temperature in September - Portland, ME
  • Average sea temperature in September: 60.5°F

The best month for swimming (with the highest average sea temperature) is August (63.7°F).
The coldest month (with the lowest average sea temperature) is March (38°F).

Average daylight in September / Average sunshine in September - Portland, ME
  • Average daylight in September: 12.5h

The month with the longest days is June (Average daylight: 15.4h).
The month with shortest days is December (Average daylight: 9h).

  • Average sunshine in September: 7.6h

The month with most sunshine is July (Average sunshine: 9.1h).
The month with least sunshine is December (Average sunshine: 4.5h).

Average UV index in September - Portland, ME
  • Average UV index in September: 5

Months with the highest UV index are June and July (UV index 8).
Months with the lowest UV index are January and December (UV index 1).