Portsmouth Weather in September
Thinking of visiting Portsmouth in September? Expect high temperatures reaching 23°C (73°F) during the day, dropping to 12°C (54°F) at night, and note that quite a bit of rainfall is likely.
Rainfall in Portsmouth in September
Based on our climate data of the past 30 years, about 9 days of rain are anticipated, with 96 mm (3.8 in) on average. When it rains this month, it tends to come down fairly heavily. Showers can be substantial even if they don't last all day.
Temperature in Portsmouth in September
If you're visiting Portsmouth in September, expect perfect temperatures with highs of 23°C (73°F) and overnight lows of 12°C (54°F). This kind of day-to-night contrast is typical for this time of year. With overnight lows of 12°C (54°F), evenings can feel noticeably cooler than the daytime. An extra layer is a good idea, though the cool air makes for a good night's sleep.
Sunshine in Portsmouth in September
Expect sunny days throughout the month, with an estimated 214 hours of sunshine. This makes it a pleasant time to visit Portsmouth.If you're a fan of comfortable temperatures and drier conditions, September is a great time to visit.
Check the conditions for any month of the year.
For a detailed overview over the year and the best time to visit the United States of America, check out our Portsmouth's climate page.
Portsmouth Temperature in September
Min Temperature
12°C (54°F)
Max Temperature
23°C (73°F)
Chance of Rain
30%
Precipitation
96 mm (3.8 in)
Rainy days
9 days
Humidity
76% *
Sunshine
214 hours *
Percentage Sunshine
*
Daily Historical Temperatures
49-year average (1976-2025)
Based on our historical records, temperatures in Portsmouth typically drop from around 25°C (77°F) at the start of September to approximately 20°C (68°F) by the end. Nights are cool, with lows typically ranging from 8°C (46°F) to 13°C (55°F).
Average temperatures in September
Daily Historical Precipitation
49-year average (1976-2025)
Average daily rainfall for each day of the month based on long-term records.
Average precipitation in September
Historical weather for Portsmouth in September
Browse day-by-day weather records for Portsmouth spanning 51 years. Select any month and year to see actual temperatures, rainfall, and conditions recorded on each day.
Portsmouth historical weather extremes in September
Based on 28 years of weather observations in Portsmouth between 1997 and 2025, these are the recorded extremes.
- Portsmouth recorded its highest September temperature of 35°C (95°F) on September 8, 2007.
- The coldest September day was on September 30, 2017, with a maximum of 12°C (54°F).
- Nighttime temperatures dropped to -3°C (27°F) on September 29, 2000, marking the coldest September night on record.
Best Places in the United States of America in September
Find out more about the weather in the United States of America and which places have the best travel conditions in this month. See all of the United States of America in September →
perfect weather
pleasant
tolerable
unpleasant
poor
What to Wear in Portsmouth in September
For Portsmouth in September, you'll want flexible clothing. It's wise to pack cotton shirts, comfortable shorts, and a pair of jeans for cooler evenings. A light sweater or jacket is useful for air-conditioned spaces (like buses) or unexpected cool moments. High rain levels are expected, so pack waterproof gear and an umbrella or poncho. You'll definitely want to pack sunglasses and sunscreen. There will be plenty of bright sunshine this month.What To Do in Portsmouth in September
We rated the following activities from 1 (least suitable) to 10 (best) to do.
Check the conditions for any month of the year.
For a detailed overview over the year and the best time to visit the United States of America, check out our Portsmouth's climate page.
Temperature Rainfall Sunshine Humidity
See the full Portsmouth climate overview or explore weather in the United States of America.
