September weather forecast
Portsmouth, RI

Share

Weather in September

September marks the start of a transitional phase in Portsmouth as summer heat gives way to relatively cooler autumn temperatures. Warm days from the summer month of August become cooler, contributing to the overall pleasant weather. The town’s foliage exudes hues of rust and gold, attributing to a decrease in precipitation. A sharp drop in cloud cover allows for clear skies, making room for a brilliant display of stars at night. The frequency of rainfall days sees a slight decline, signaling a change in weather pattern with the onset of a drier season.

Temperature

The average high-temperature slightly decreases in September, shifting from a moderately hot 77.7°F (25.4°C) in August to an agreeable 71.4°F (21.9°C). During the month of September, Portsmouth anticipates a mean low-temperature of 59.7°F (15.4°C).

Humidity

In September, the average relative humidity is 78%.

Rainfall

September is the month with the least rainfall. Rain falls for 11.6 days and accumulates 1.42" (36mm) of precipitation.

Snowfall

April, June through October are months without snowfall.

Daylight

In September, the average length of the day is 12h and 28min.
On the first day of September in Portsmouth, sunrise is at 6:11 am and sunset at 7:17 pm. On the last day of the month, sunrise is at 6:41 am and sunset at 6:27 pm EDT.

Sunshine

The average sunshine in September in Portsmouth is 8.7h.

UV index

In September, the average daily maximum UV index is 4. A UV Index reading of 3 to 5 represents a moderate threat to health from unsafe exposure to UV radiation for the average person.
Note: A daily maximum UV index of 4 in September translates into the following instructions:
Stay alert. Light-skinned people could suffer burns in less than 30 minutes. To prevent harmful UV exposure, minimize direct contact with the Sun around midday. 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.
[Resources]

Frequently asked questions

What is the temperature in September in Portsmouth?

In September, in Portsmouth, the average high-temperature is 71.4°F (21.9°C), and the average low-temperature is 59.7°F (15.4°C).

What is the average humidity in September in Portsmouth?

In Portsmouth, the average relative humidity in September is 78%.

What is the driest month in Portsmouth?

The month with the least rainfall in Portsmouth is September, when the rain falls for 11.6 days and typically collects 1.42" (36mm) of precipitation.

How much does it rain in Portsmouth in September?

In Portsmouth, Rhode Island, during September, the rain falls for 11.6 days and regularly aggregates up to 1.42" (36mm) of precipitation.

When it does not snow in Portsmouth?

In Portsmouth, snow does not fall in April, June through October.

How many hours of daylight does Portsmouth have in September?

In Portsmouth, the average day length in September is 12h and 28min.

When is the sunrise / sunset in September in Portsmouth?

On the first day of September in Portsmouth, Rhode Island, sunrise is at 6:11 am and sunset at 7:17 pm. On the last day of the month, sunrise is at 6:41 am and sunset at 6:27 pm EDT.

How many hours of sunshine does Portsmouth have in September?

In Portsmouth, the average sunshine duration in September is 8.7h.

What is the UV index intensity in September in Portsmouth?

In Portsmouth, the average daily maximum UV index in September is 4. A UV Index of 3 to 5 symbolizes a moderate vulnerability from exposure to the Sun's UV radiation.
Average humidity
Average rainfall days
Average snowfall
Average snowfall days
Average daylight
Average sunshine
Average sunshine days
Average UV index
Average cloud cover
Average visibility

Average temperature in September
Portsmouth, RI

Average temperature in September - Portsmouth, RI
  • Average high temperature in September: 71.4°F

The warmest month (with the highest average high temperature) is July (78.3°F).
The month with the lowest average high temperature is January (36.1°F).

  • Average low temperature in September: 59.7°F

The month with the highest average low temperature is July (66.7°F).
The coldest month (with the lowest average low temperature) is January (26.4°F).

[Resources]

Average pressure in September
Portsmouth, RI

Average pressure in September - Portsmouth, RI
  • Average pressure in September: 30.05"Hg

The month with the highest atmospheric pressure is November (30.07"Hg).
The month with the lowest atmospheric pressure is June (29.93"Hg).

[Resources]

Average wind speed in September
Portsmouth, RI

Average wind speed in September - Portsmouth, RI
  • Average wind speed in September: 9mph

The windiest month (with the highest average wind speed) is January (12.1mph).
The calmest month (with the lowest average wind speed) is August (8.1mph).

[Resources]

Average humidity in September
Portsmouth, RI

Average humidity in September - Portsmouth, RI
  • Average humidity in September: 78%

The month with the highest relative humidity is June (81%).
The month with the lowest relative humidity is March (73%).

[Resources]

Average rainfall in September
Portsmouth, RI

Average rainfall in September - Portsmouth, RI
  • Average rainfall in September: 1.42"

The wettest month (with the highest rainfall) is October (3.27").
The driest month (with the least rainfall) is September (1.42").

[Resources]

Average rainfall days in September
Portsmouth, RI

Average rainfall days in September - Portsmouth, RI
  • Average rainfall days in September: 11.6 days

The month with the highest number of rainy days is April (15.6 days).
The month with the least rainy days is January (8.3 days).

[Resources]

Average snowfall in September
Portsmouth, RI

Average snowfall in September - Portsmouth, RI
  • Average snowfall in September: 0"

The month with the highest snowfall is February (2.76").
The months with the least snowfall are April, June, July, August, September and October (0").

[Resources]

Average snowfall days in September
Portsmouth, RI

Average snowfall days in September - Portsmouth, RI
  • Average snowfall days in September: 0 days

The month with the highest number of snowfall days is January (6.6 days).
The months with the least snowfall days are June, July, August, September and October (0 days).

[Resources]

Average daylight in September /
Average sunshine in September
Portsmouth, RI

Average daylight in September / Average sunshine in September - Portsmouth, RI
  • Average daylight in September: 12h and 3min

The month with the longest days is June (Average daylight: 15h and 6min).
The month with the shortest days is December (Average daylight: 9h and 12min).

  • Average sunshine in September: 8h and 4min

The month with the most sunshine is August (Average sunshine: 10h and 30min).
The month with the least sunshine is February (Average sunshine: 4h and 48min).

[Resources]

Average sunshine days in September
Portsmouth, RI

Average sunshine days in September - Portsmouth, RI
  • Average sunshine days in September: 15.8 days

The month with the most sunshine days is November (17.7 days).
The month with the least sunshine days is April (12.3 days).

[Resources]

Average UV index in September
Portsmouth, RI

Average UV index in September - Portsmouth, RI
  • Average UV index in September: 4

The months with the highest UV index are June, July and August (UV index 6).
The months with the lowest UV index are January, February, March and December (UV index 2).

[Resources]

Average cloud cover in September
Portsmouth, RI

Average cloud cover in September - Portsmouth, RI
  • Average cloud cover in September: 33

The month with the most cloud cover is March (Cloud cover 48).
The month with the least cloud cover is August (Cloud cover 29).

[Resources]

Average visibility in September
Portsmouth, RI

Average visibility in September - Portsmouth, RI
  • Average visibility in September: 6mi

The months with the highest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
The months with the lowest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).

[Resources]

Portsmouth, Rhode Island, USA

Weather forecast for your location

1. Click Locate me button
2. Allow the app to use your location