Click on a day for an hourly weather forecast
The temperatures in Portsmouth in September are usually low and can range between 13°C and 18°C.
You can expect about 3 to 8 days of rain in Portsmouth during the month of September. It’s a good idea to bring along your umbrella so that you don’t get caught in poor weather.
Our weather forecast can give you a great sense of what weather to expect in Portsmouth in September 2025.
If you’re planning to visit Portsmouth in the near future, we highly recommend that you review the 14 day weather forecast for Portsmouth before you arrive.
| Month | Temperatures | Rainy Days | Dry Days | Snowy Days | Rainfall | Weather | More details |
|---|---|---|---|---|---|---|---|
| January | 8° / 4° | 9 | 19 | 2 | 108 mm | Awful | Portsmouth in January |
| February | 8° / 5° | 8 | 18 | 2 | 88 mm | Awful | Portsmouth in February |
| March | 10° / 5° | 6 | 25 | 1 | 69 mm | Ok | Portsmouth in March |
| April | 12° / 7° | 5 | 25 | 0 | 57 mm | Ok | Portsmouth in April |
| May | 15° / 9° | 5 | 26 | 0 | 69 mm | Good | Portsmouth in May |
| June | 17° / 12° | 5 | 25 | 0 | 89 mm | Good | Portsmouth in June |
| July | 20° / 14° | 5 | 26 | 0 | 79 mm | Good | Portsmouth in July |
| August | 20° / 15° | 5 | 26 | 0 | 82 mm | Good | Portsmouth in August |
| September | 18° / 13° | 5 | 25 | 0 | 68 mm | Good | Portsmouth in September |
| October | 15° / 11° | 8 | 23 | 0 | 126 mm | Ok | Portsmouth in October |
| November | 11° / 8° | 8 | 21 | 0 | 127 mm | Bad | Portsmouth in November |
| December | 9° / 6° | 9 | 21 | 1 | 122 mm | Bad | Portsmouth in December |