| Month | High | Low | Rain | Wet days | Score |
|---|---|---|---|---|---|
| January | 9.7° | 0.3° | 86.9mm | 10.2 | 44 |
| February | 11.3° | 1.3° | 81.1mm | 9.6 | 52 |
| March | 15.3° | 4.8° | 97.8mm | 10.3 | 64 |
| April | 20.9° | 9.6° | 93.1mm | 10.4 | 79 |
| May | 24.9° | 14.6° | 114.3mm | 11.6 | 77 |
| June | 29.2° | 19.2° | 128.4mm | 10.5 | 70 |
| July | 31.4° | 21.8° | 152.5mm | 11 | 60 |
| August | 30.2° | 21.3° | 174.3mm | 11 | 65 |
| September | 27° | 18.5° | 154.4mm | 9.2 | 82 |
| October | 21.6° | 12.3° | 102.1mm | 8.2 | 84 |
| November | 16° | 6.3° | 89.9mm | 8.3 | 71 |
| December | 12.2° | 2.6° | 98.1mm | 9.8 | 55 |
January in Portsmouth averages a daily high of 9.7°C with nights around 0.3°C. Expect roughly 10.2 wet days totalling 86.9mm. Demanding conditions — pack for it and plan indoor options.
February in Portsmouth averages a daily high of 11.3°C with nights around 1.3°C. Expect roughly 9.6 wet days totalling 81.1mm. Demanding conditions — pack for it and plan indoor options.
March in Portsmouth averages a daily high of 15.3°C with nights around 4.8°C. Expect roughly 10.3 wet days totalling 97.8mm. Generally workable, with some weather to plan around.
April in Portsmouth averages a daily high of 20.9°C with nights around 9.6°C. Expect roughly 10.4 wet days totalling 93.1mm. Comfortable conditions for being outdoors all day.
May in Portsmouth averages a daily high of 24.9°C with nights around 14.6°C. Expect roughly 11.6 wet days totalling 114.3mm. Comfortable conditions for being outdoors all day.
June in Portsmouth averages a daily high of 29.2°C with nights around 19.2°C. Expect roughly 10.5 wet days totalling 128.4mm. Generally workable, with some weather to plan around.
July in Portsmouth averages a daily high of 31.4°C with nights around 21.8°C. Expect roughly 11 wet days totalling 152.5mm. Generally workable, with some weather to plan around.
August in Portsmouth averages a daily high of 30.2°C with nights around 21.3°C. Expect roughly 11 wet days totalling 174.3mm. Generally workable, with some weather to plan around.
September in Portsmouth averages a daily high of 27°C with nights around 18.5°C. Expect roughly 9.2 wet days totalling 154.4mm. Comfortable conditions for being outdoors all day.
October in Portsmouth averages a daily high of 21.6°C with nights around 12.3°C. Expect roughly 8.2 wet days totalling 102.1mm. Comfortable conditions for being outdoors all day.
November in Portsmouth averages a daily high of 16°C with nights around 6.3°C. Expect roughly 8.3 wet days totalling 89.9mm. Generally workable, with some weather to plan around.
December in Portsmouth averages a daily high of 12.2°C with nights around 2.6°C. Expect roughly 9.8 wet days totalling 98.1mm. Generally workable, with some weather to plan around.
Each month scores out of 100. It starts at 100 and loses points for daytime highs outside a 20–27°C band, for wet days, and for nights below 2°C. Nothing else is weighted in — no crowd data, no prices, no opinion. Portsmouth peaks at 84.
Based on 30 years of records, April–May scores highest for comfort in Portsmouth, balancing daytime temperature against rainfall.
July is the warmest, averaging a daily high of 31.4°C.
August is the wettest, averaging 174.3mm of rain across roughly 11 wet days.
January is the coolest month, with average daily highs around 9.7°C.