Portsmouth
New Hampshire, USA
Long-term weather forecast
Long-term weather forecast

September weather forecast and climate
Portsmouth, NH

Bright neon lights and buildings next to the very calm waters of the iconic Piscataqua River in Portsmouth, New Hampshire, the clear dusk sky in close up view
Bright neon lights and buildings next to the very calm waters of the iconic Piscataqua River in Portsmouth, New Hampshire, the clear dusk sky in close up view
The first month of the autumn, September, is still a pleasant month in Portsmouth, New Hampshire, with average temperature ranging between min 52°F (11.1°C) and max 70°F (21.1°C).

Temperature

In September, the average high-temperature marginally drops, from a warm 77°F (25°C) in August, to an agreeable 70°F (21.1°C). In September, the average low-temperature is 52°F (11.1°C).

Rainfall

In September, in Portsmouth, New Hampshire, the rain falls for 8 days. Throughout September, 3.4" (87mm) of precipitation is accumulated. In Portsmouth, during the entire year, the rain falls for 125 days and collects up to 42.4" (1078mm) of precipitation.

Ocean temperature

In Portsmouth, New Hampshire, the average seawater temperature in September is 61.9°F (16.6°C). Swimming in 61.9°F (16.6°C) is not enjoyable for the majority. Controlling breathing becomes progressively more difficult as surface water temperature decreases below 69.8°F (21°C).

Daylight

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

Sunshine

The average sunshine in Portsmouth, New Hampshire, is 8h.

UV index

In Portsmouth, New Hampshire, the average daily maximum UV index in September is 6. A UV Index reading of 6 to 7 represents a high health vulnerability from the exposure to the Sun's UV radiation for ordinary individuals.
In September, the average maximum UV index of 6 translate into the following recommendations:
Take precautions against overexposure. Protection against sun damage is needed. Seek shade and minimize exposure to direct Sun in a period between 10 a.m. and 4 p.m. when UV radiation is most intense; keep in mind that shade structures like parasols or canopies do not provide perfect sun protection. 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 Portsmouth?

In September, in Portsmouth, New Hampshire, the average high-temperature is 70°F (21.1°C), and the average low-temperature is 52°F (11.1°C).

How much does it rain in Portsmouth in September?

In Portsmouth, New Hampshire, in September, during 8 rainfall days, 3.4" (87mm) of precipitation is typically accumulated.

What is the ocean temperature in September in Portsmouth?

In Portsmouth, in September, the average water temperature is 61.9°F (16.6°C). For swimming, a surface water temperature of 61.9°F (16.6°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 Portsmouth?

In September, the average length of the day in Portsmouth, New Hampshire, is 12.5h.

How long on average sun shines in September in Portsmouth?

In September, the average sunshine in Portsmouth is 8h.

What is the UV index intensity in September in Portsmouth?

The average daily maximum UV index in September in Portsmouth is 6. A UV Index estimate of 6 to 7 represents a high health risk from unprotected exposure to the UV radiation.
Average temperature in September - Portsmouth, NH
  • Average high temperature in September: 70°F

The warmest month (with the highest average high temperature) is July (79°F).
Months with the lowest average high temperature are January and February (32°F).

  • Average low temperature in September: 52°F

The month with the highest average low temperature is July (61°F).
The coldest month (with the lowest average low temperature) is January (16°F).

Average rainfall in September - Portsmouth, NH
  • Average rainfall in September: 3.4"

The wettest month (with the highest rainfall) is November (4.9").
The driest month (with the lowest rainfall) is August (2.8").

Average rainfall days in September - Portsmouth, NH
  • Average rainfall days in September: 8 days

Months with the highest number of rainy days are May and December (12 days).
The month with the lowest number of rainy days is September (8 days).

Average sea temperature in September - Portsmouth, NH
  • Average sea temperature in September: 61.9°F

The best month for swimming (with the highest average sea temperature) is August (65.6°F).
The coldest month (with the lowest average sea temperature) is March (38.5°F).

Average daylight in September / Average sunshine in September - Portsmouth, NH
  • Average daylight in September: 12.5h

The month with the longest days is June (Average daylight: 15.3h).
The month with shortest days is December (Average daylight: 9.1h).

  • Average sunshine in September: 8h

Months with most sunshine are June, July and August (Average sunshine: 9h).
Months with least sunshine are January, November and December (Average sunshine: 5).

Average UV index in September - Portsmouth, NH
  • Average UV index in September: 6

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).