Portsmouth records about 740mm of rain across roughly 118 wet days a year, which is a 32% chance on an average day. December is the wettest month at 72mm (10% of the annual total) and May the driest at 42mm. Local rain type: drizzle. Portsmouth on England's south coast gets less rain than London. The Historic Dockyard provides excellent shelter during Channel weather.
Chance of rain on an average day: 32%
Rainfall climatology for Portsmouth. The live hour-by-hour answer for today loads at the top of this page from Open-Meteo and refreshes through the day — the figures below describe a typical year, not today.
Last updated: · Live forecast data refreshes hourly.
| Annual rainfall | 740mm |
| Rain days per year | 118 |
| Odds on an average day | 32% |
| Wettest month | December — 72mm over 13 days |
| Driest month | May — 42mm over 8 days |
| Rain type | drizzle |
| Best dry window | May through July offers the driest conditions for coastal walks. |
| Worst rain window | October through December brings Channel storms. |
December delivers 71% more rain than May (72mm vs 42mm). That gap is the difference between planning around showers and ignoring them.
No single month holds more than 10% of the annual total, so rain in Portsmouth is spread through the year — there is no season you can rely on being dry.
Portsmouth rain is mostly persistent drizzle, where a waterproof shell beats an umbrella.
Rain falls on about 13 days in December against 8 in May — the frequency swing matters more for planning than the millimetre totals.
Climate normals. Use them to judge whether today's live forecast at the top of the page is typical or unusual for the season.
| Month | Rainfall | Rain days | Chance on a given day | Highs |
|---|---|---|---|---|
| January | 72mm | 13 | 43% | 8°C |
| February | 48mm | 9 | 30% | 8°C |
| March | 48mm | 9 | 30% | 10°C |
| April | 48mm | 9 | 30% | 13°C |
| May | 42mm | 8 | 27% | 16°C |
| June | 42mm | 8 | 27% | 19°C |
| July | 42mm | 8 | 27% | 21°C |
| August | 48mm | 9 | 30% | 21°C |
| September | 52mm | 9 | 30% | 19°C |
| October | 72mm | 13 | 43% | 16°C |
| November | 72mm | 13 | 43% | 13°C |
| December | 72mm | 13 | 43% | 10°C |
Rain probability is the chance that at least 0.2mm falls at your location — not how long it rains. For Portsmouth we combine the hourly probability curve, expected volume in millimetres, and the city's own rainfall record into a single umbrella verdict.
| Factor | Weight | What it measures |
|---|---|---|
| Hourly probability | 40% | Peak and sustained chance of measurable rain across the next 24 hours. |
| Expected volume | 30% | Total millimetres, which separates a passing shower from a genuine soaking. |
| Timing & duration | 20% | When rain starts, when it eases, and the longest continuous dry window. |
| Local rain type | 10% | Drizzle, brief showers, thunderstorms or monsoon — each needs different gear. |
Live hourly values come from Open-Meteo and refresh through the day. Monthly rainfall figures are climate normals, so they describe a typical year rather than a forecast.
Portsmouth records rain on roughly 118 days a year — about a 32% chance on any given day — totalling around 740mm.
December, with about 72mm over 13 rain days. That is 10% of the entire year's rainfall in a single month.
May is the driest month at 42mm across roughly 8 days. May through July offers the driest conditions for coastal walks.
Portsmouth on England's south coast gets less rain than London. The Historic Dockyard provides excellent shelter during Channel weather.
No. Probability is the chance that at least 0.2mm of rain falls at your location at some point in the period. Check the expected millimetres alongside it: 40% with 0.4mm is a passing shower, 40% with 12mm is a soaking.