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Portsmouth Weather by Month
Average temperatures, rainfall and humidity for Portsmouth, United States, month by month, built from OpenWeather's historical records. Use it to see what a typical Portsmouth month looks like before you travel — then check the live Portsmouth forecast for the days ahead.
Warmest month
July
28°C average high
Coolest month
January
-7°C average low
Wettest month
October
86 mm of rain
Driest month
February
29 mm of rain
Average temperature and rainfall in Portsmouth by month
Averages of the daily highs and lows recorded in each month, with total rainfall, mean humidity and mean wind speed.
| Month | Avg high | Avg low | Record low / high | Rainfall | Humidity | Wind |
|---|---|---|---|---|---|---|
| January | 1°C | -7°C | -22°C / 19°C | 42 mm | 69% | 11 km/h |
| February | 3°C | -6°C | -25°C / 24°C | 29 mm | 68% | 11 km/h |
| March | 7°C | -2°C | -19°C / 24°C | 49 mm | 63% | 12 km/h |
| April | 14°C | 3°C | -9°C / 31°C | 72 mm | 62% | 12 km/h |
| May | 21°C | 9°C | -1°C / 34°C | 80 mm | 66% | 10 km/h |
| June | 25°C | 14°C | 3°C / 37°C | 84 mm | 71% | 8 km/h |
| July | 28°C | 18°C | 11°C / 36°C | 78 mm | 73% | 8 km/h |
| August | 27°C | 16°C | 8°C / 36°C | 64 mm | 74% | 8 km/h |
| September | 23°C | 13°C | 1°C / 33°C | 76 mm | 75% | 8 km/h |
| October | 16°C | 7°C | -6°C / 29°C | 86 mm | 76% | 9 km/h |
| November | 9°C | 1°C | -14°C / 25°C | 56 mm | 71% | 10 km/h |
| December | 4°C | -3°C | -21°C / 17°C | 71 mm | 74% | 10 km/h |
Best time to visit Portsmouth
The most comfortable time to visit Portsmouth is generally June and August to September, balancing mild daytime temperatures against the driest stretch of the year. The city has strongly marked seasons and rain concentrates around October, totalling about 787 mm a year.
Travellers who prefer heat should aim for July, when highs average 28°C. October is the month to avoid if rain would spoil your plans — it averages 86 mm, roughly 3× the rainfall of February.
Source: OpenWeather historical and statistical weather data. Values are long-term averages, not a forecast — see the Portsmouth forecast for what is happening now.