Sea temperature by month
Average sea surface temperature off Brighton, 2023 to 2025. The vertical dashed line is 15°C, the point the RNLI uses to define cold water. Bars to its left are cold by that measure; the thin black line on each bar spans the coldest and warmest daily average in that month.
| Month | Average | Coldest day | Warmest day | Range |
|---|---|---|---|---|
| January | 8.6 | 7.0 | 10.4 | Under 10° |
| February | 8.3 | 7.3 | 9.5 | Under 10° |
| March | 8.7 | 7.1 | 9.8 | Under 10° |
| April | 10.7 | 9.4 | 13.3 | 10–15° |
| May | 13.5 | 11.5 | 15.9 | 10–15° |
| June | 16.4 | 13.4 | 18.9 | 15–18° |
| July | 18.3 | 16.0 | 20.6 | Over 18° |
| August | 19.3 | 17.6 | 20.9 | Over 18° |
| September | 18.3 | 16.6 | 20.5 | Over 18° |
| October | 16.1 | 13.6 | 18.4 | 15–18° |
| November | 13.1 | 10.9 | 15.0 | 10–15° |
| December | 10.4 | 9.0 | 11.6 | 10–15° |
Three things stand out. The sea lags the air: it is warmest in August and coldest in February, a month or two after the air peaks and bottoms out. Spring climbs fastest, from 10.7° in April to 16.4° in June. And a single month moves around more than the averages suggest: July daily averages ran from 16.0 to 20.6°, so a colder or warmer week than the table is normal.
Where the numbers come from
The live figure and the monthly table both use Open-Meteo's marine model, for the sea cell nearest Brighton (50.81, -0.14). Hourly values were collapsed to daily means, then averaged by calendar month over 2023 to 2025. It is a model, not a buoy or a thermometer on the groyne. Water right at the shoreline, in a hot spell or after a cold snap, can read differently from the open-sea value.
Treat it as a good guide to the season. Nobody should use it as the only check before getting in: tides, wind and swell matter more on the day, and the sea swimming guide covers what to look at. Tide times are on VisitBrighton.
What each range is like
The RNLI defines cold water as 15°C and below and puts the average UK and Irish sea at 12°C. Brighton is below 15° on average for 7 months of the year. Here is how the monthly averages group, with what the RNLI and local venues say about each.
| Range | Months | What to expect |
|---|---|---|
| Under 10° | Jan, Feb, Mar | The coldest the sea gets here. The RNLI describes a dip as a few minutes at a time, and its kit list for dips includes a wetsuit, booties and gloves. For scale, Recovery Room Hove says its plunge pools are set at 5 to 8°C, so February sea is not far above that, with waves and a tide added. |
| 10° to 15° | Apr, May, Nov, Dec | Still cold water by the RNLI's measure. Spring is the trap: the air can feel warm while the sea is under 14° (13.5° in May on average). |
| 15° to 18° | Jun, Oct | Averages clear the RNLI line, but the RNLI still warns that cold water shock can happen in summer. Daily readings in these months range from 13.4 to 18.9° (June) and 13.6 to 18.4° (October). |
| Over 18° | Jul, Aug, Sep | The warmest the sea gets here, and what most visitors mean by warm enough to swim. Individual days still drop to 16.0° in July and 16.6° in September. |
Wetsuit or not
No source sets a temperature at which a wetsuit becomes compulsory. What the sources say is consistent. The RNLI says it is safest to wear a wetsuit for a cold water dip because it increases buoyancy and lowers the chance of cold water shock. Brighton & Hove City Council gives the same advice for sea swimming on the city's shingle beaches.
On the averages above, the case for one is strongest from November to May, when the sea is below 15°. From June to October it comes down to how long you plan to be in, the wind, and how you cope with cold. Gloves, boots and a bright swim hat are on the RNLI's kit list too.
Sauna, then the sea
Two beach saunas in Brighton sit on Madeira Drive with sea access, so the sauna is on one side of the shingle and the water is on the other. Neither publishes a sea temperature; use the table above. Prices below are the cheapest standard shared session each venue lists. For a plunge without the waves, compare cold plunge and ice baths in Brighton.
£12.5045 min
Four wood-fired saunas, with the sea steps away. The ticket also covers a cool plunge pool and a chilled steel tub for days the sea is not an option. Sea shoes are essential on the pebbles.
£830 min
Communal sessions in 30-minute blocks, two plunge pools, cold showers and direct access to the sea. Swimwear is required, and the venue says to wear flip-flops on the pebbles.
Do the sea part with the same care as any dip: read the sea swimming guide for sewage alerts, lifeguard dates and cold water shock, and keep alcohol out of the plan. Beach Box bans it outright, and the council says it is never safe to go into the sea after drinking. New to saunas? Start with the first-timer guide.
Questions
What is the sea temperature in Brighton today?
The live reading is at the top of this page and refreshes each time it loads. It comes from the Open-Meteo marine model for the sea off Brighton seafront, so it is a modelled value, not a thermometer in the water. For this time of year, October, the 2023 to 2025 average is 16.1°C.
How warm is the sea in Brighton in August?
August is the warmest month, averaging 19.3°C across 2023 to 2025. Daily average readings that month ran from 17.6 to 20.9°C.
What is the coldest the sea gets in Brighton?
February is the coldest month on average at 8.3°C. The single coldest daily average in the data was 7.0°C, in January.
Do I need a wetsuit to swim in the sea at Brighton?
There is no single temperature at which one becomes compulsory. The RNLI and Brighton & Hove City Council both say a wetsuit is the safest option for cold-water dips because it adds buoyancy and lowers the chance of cold water shock. On these averages the sea is below 15°C from November to May. If you have a heart or blood pressure condition or take regular medication, talk to a healthcare professional first.
Does a hot day mean the sea is warm?
No. The sea lags the air by weeks. Brighton's sea is warmest in August and coldest in February, not July and January.
Can you sauna and then dip in the sea in Brighton?
Yes, at two venues. Beach Box Spa and Luna Hut Sea Lanes both sit on the beach at Madeira Drive and have direct sea access, so you can move between sauna rounds and the sea. Both also have plunge options for days when the sea is not usable.
Sources
- Open-Meteo Marine Weather API Hourly modelled sea surface temperature for 50.81, -0.14, 2023 to 2025, averaged by month. Live reading from the same service.
- RNLI: cold water shock The 15°C cold-water line and the 12°C UK average.
- RNLI: top tips for cold water dips Wetsuit, booties and gloves, a few minutes at a time.
- Brighton & Hove City Council: sea swimming safety Wetsuit advice, medical conditions, tide times.
- VisitBrighton: tide timetables
- Beach Box Spa and Luna Hut Sea Lanes Venue facts from our checked venue pages.
Compare venues
More guides
- Sea swimming in BrightonWater quality, sewage alerts, currents and cold water shock.
- Your first sauna in BrightonWhat happens, what to bring, what it costs.
- Sauna etiquetteWhat to wear, towels, silence, Aufguss.
- All Brighton & Hove guidesSea, safety and sauna manners.
- All Brighton & Hove saunasPrices, sea dips, cold plunges.