UK
Best Time to Dive in Cornwall
50.03°N 5.04°W
The best conditions run May to September for the long days — 14.7 hours of light against 10.0. The marine life holds steady all year, so the weather picks the month. The wider season runs April to September.
- Best time
- May–Sep
- Water
- 10–17 °C
- Visibility
- 5–20 m
- Season runs
- Apr–Sep
- Dived from
- day boat and shore diving
- Tidal range
- 2.3–4.7 m
- Species logged
- 11
Worth knowing: 46% of days see seas over 1.5 m.
Where it is
111 km across · coastline from Natural Earth 10m
Diving in Cornwall — monthly breakdown
A year of scuba diving conditions at a glance. Hover a month to isolate it.
| January | February | March | April | May | June | July | August | September | October | November | December | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Conditions | Poor | Poor | Poor | Good | Excellent | Excellent | Excellent | Excellent | Good | Poor | Poor | Poor |
| Water temp (°C) | 11 | 10 | 10 | 11 | 13 | 15 | 17 | 17 | 16 | 15 | 13 | 12 |
| Visibility (m) | 10–20 | 5–15 | 5–15 | 5–15 | 5–15 | 10–20 | 10–20 | 5–15 | 5–15 | 10–20 | 10–20 | — |
| Marine life | Peak | Peak | Peak | Peak | Peak | Peak | Peak | Peak | Peak | Peak | Peak | Peak |
| Best time | Peak | Peak | Peak | Peak | Peak |
Excellent Good Moderate PoorPeak season May–Sep
Long-term averages, 2016–2025. Visibility is estimated from satellite chlorophyll-a. Water temperature is the surface mean; it is cooler at depth.
The Cornwall diving season
April to September · Peak season
6 monthsJFMAMJJASOND
- Water temperature
- 11–17 °C
- Visibility
- 5–15 m
- Rain
- 13 days a month
Diving conditionsThe wind eases.
Marine lifeBasking shark (near-guaranteed), Ocean sunfish (near-guaranteed), Grey seal (near-guaranteed), Blue shark (likely) peak at Cornwall in these months.
October to March · Off season
6 monthsJFMAMJJASOND
- Water temperature
- 10–15 °C
- Visibility
- 10–20 m
- Rain
- 16 days a month
Diving conditionsThe wind is up. The sea is rougher.
Marine lifeGrey seal (near-guaranteed) peaks at Cornwall in these months.
- Spring tides run 4.7 m against 2.3 m on neaps, so currents build around the full and new moon.
- Water temperature is satellite sea-surface temperature, so expect it cooler below the thermocline.
- Visibility is estimated from satellite chlorophyll-a.
Cornwall water temperature and weather
9,513 underwater observation records · 32 surveyed years of ocean data · 10 years of sea temperature
Water & weather
Cornwall water temperature by month
The dashed line is the monthly average. Eight days in ten fall inside the band.
10th to 90th percentile rangemonthly mean
19
rough days a month
Seas top 1.5 m on 64% of days. Enough to cancel a day boat
6
blowy days a month
Gusts over 40 km/h, about where a day boat stays in port
14
wet days a month
3 of them bring heavy rain
| Month | Swell | Gusts over 40 km/h | Wet days | Heavy rain | Air | Daylight |
|---|---|---|---|---|---|---|
| January | 4.8 m | 30% | 15 | 4 | 10 °C | 8.3 h |
| February | 4.1 m | 36% | 15 | 3 | 10 °C | 9.8 h |
| March | 4.1 m | 28% | 16 | 4 | 11 °C | 11.6 h |
| April | 3.4 m | 11% | 11 | 2 | 12 °C | 13.5 h |
| May | 2.3 m | 8% | 13 | 1 | 15 °C | 15.2 h |
| June | 2.4 m | 5% | 14 | 2 | 17 °C | 16.1 h |
| July | 2.4 m | 5% | 13 | 2 | 19 °C | 15.7 h |
| August | 2.5 m | 7% | 14 | 3 | 19 °C | 14.3 h |
| September | 3.3 m | 15% | 15 | 3 | 18 °C | 12.4 h |
| October | 4.1 m | 21% | 15 | 5 | 15 °C | 10.4 h |
| November | 4.8 m | 31% | 16 | 4 | 12 °C | 8.7 h |
| December | 4.5 m | 40% | 17 | 5 | 11 °C | 7.9 h |
Swell is the rough end of the month: nine days in ten come in under it. Sea temperature covers 10 years, waves 4.
Pick your week
48 weeks from the daily record. Darker is better, against this site's own year. Pick a month for the detail.
| Week 1 | January week 1: Poor | February week 1: Poor | March week 1: Poor | April week 1: Moderate | May week 1: Excellent | June week 1: Excellent | July week 1: Excellent | August week 1: Excellent | September week 1: Good | October week 1: Moderate | November week 1: Poor | December week 1: Poor |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Week 2 | January week 2: Poor | February week 2: Poor | March week 2: Poor | April week 2: Good | May week 2: Excellent | June week 2: Excellent | July week 2: Excellent | August week 2: Excellent | September week 2: Good | October week 2: Moderate | November week 2: Poor | December week 2: Poor |
| Week 3 | January week 3: Poor | February week 3: Poor | March week 3: Moderate | April week 3: Excellent | May week 3: Excellent | June week 3: Excellent | July week 3: Excellent | August week 3: Excellent | September week 3: Good | October week 3: Poor | November week 3: Poor | December week 3: Poor |
| Week 4 | January week 4: Poor | February week 4: Poor | March week 4: Poor | April week 4: Excellent | May week 4: Excellent | June week 4: Excellent | July week 4: Good | August week 4: Good | September week 4: Good | October week 4: Poor | November week 4: Poor | December week 4: Poor |
Excellent Good Moderate PoorBest week to go: second of July
January, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 11 °C | 5.0 m | 35 km/h | 48% |
| Week 2 | Poor | 11 °C | 4.7 m | 33 km/h | 43% |
| Week 3 | Poor | 11 °C | 4.5 m | 31 km/h | 44% |
| Week 4 | Poor | 10 °C | 4.3 m | 33 km/h | 48% |
February, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 10 °C | 3.7 m | 35 km/h | 50% |
| Week 2 | Poor | 10 °C | 3.8 m | 35 km/h | 55% |
| Week 3 | Poor | 10 °C | 4.6 m | 35 km/h | 54% |
| Week 4 | Poor | 10 °C | 4.6 m | 34 km/h | 50% |
March, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 10 °C | 3.9 m | 34 km/h | 57% |
| Week 2 | Poor | 10 °C | 4.3 m | 34 km/h | 54% |
| Week 3 | Moderate | 10 °C | 4.0 m | 31 km/h | 44% |
| Week 4 | Poor | 10 °C | 4.0 m | 30 km/h | 46% |
April, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Moderate | 10 °C | 4.5 m | 29 km/h | 44% |
| Week 2 | Good | 10 °C | 3.9 m | 26 km/h | 37% |
| Week 3 | Excellent | 11 °C | 2.6 m | 25 km/h | 35% |
| Week 4 | Excellent | 11 °C | 2.3 m | 24 km/h | 37% |
May, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Excellent | 12 °C | 2.1 m | 23 km/h | 41% |
| Week 2 | Excellent | 12 °C | 2.3 m | 23 km/h | 43% |
| Week 3 | Excellent | 13 °C | 2.4 m | 24 km/h | 42% |
| Week 4 | Excellent | 14 °C | 2.2 m | 24 km/h | 41% |
June, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Excellent | 14 °C | 2.2 m | 24 km/h | 43% |
| Week 2 | Excellent | 15 °C | 2.3 m | 23 km/h | 45% |
| Week 3 | Excellent | 15 °C | 2.3 m | 24 km/h | 43% |
| Week 4 | Excellent | 16 °C | 2.4 m | 25 km/h | 45% |
July, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Excellent | 16 °C | 2.3 m | 24 km/h | 41% |
| Week 2 | Excellent | 16 °C | 2.4 m | 23 km/h | 32% |
| Week 3 | Excellent | 17 °C | 2.5 m | 23 km/h | 39% |
| Week 4 | Good | 17 °C | 2.4 m | 24 km/h | 50% |
August, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Excellent | 17 °C | 2.3 m | 25 km/h | 48% |
| Week 2 | Excellent | 17 °C | 2.3 m | 25 km/h | 46% |
| Week 3 | Excellent | 17 °C | 2.5 m | 25 km/h | 47% |
| Week 4 | Good | 17 °C | 3.1 m | 24 km/h | 44% |
September, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Good | 17 °C | 3.2 m | 25 km/h | 46% |
| Week 2 | Good | 17 °C | 3.2 m | 25 km/h | 48% |
| Week 3 | Good | 16 °C | 3.2 m | 25 km/h | 46% |
| Week 4 | Good | 16 °C | 3.6 m | 27 km/h | 49% |
October, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Moderate | 15 °C | 3.6 m | 29 km/h | 44% |
| Week 2 | Moderate | 15 °C | 3.2 m | 28 km/h | 40% |
| Week 3 | Poor | 15 °C | 4.1 m | 30 km/h | 50% |
| Week 4 | Poor | 14 °C | 4.5 m | 34 km/h | 58% |
November, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 14 °C | 4.8 m | 35 km/h | 59% |
| Week 2 | Poor | 14 °C | 4.6 m | 34 km/h | 53% |
| Week 3 | Poor | 13 °C | 4.8 m | 32 km/h | 52% |
| Week 4 | Poor | 13 °C | 4.9 m | 31 km/h | 54% |
December, week by week
| Week | Conditions | Water | Swell | Wind | Rain chance |
|---|---|---|---|---|---|
| Week 1 | Poor | 13 °C | 4.5 m | 33 km/h | 57% |
| Week 2 | Poor | 12 °C | 4.5 m | 37 km/h | 59% |
| Week 3 | Poor | 12 °C | 4.3 m | 37 km/h | 55% |
| Week 4 | Poor | 11 °C | 4.9 m | 37 km/h | 52% |
10 years of daily records, averaged into weeks.
Gear & storms
What to wear
Off the coldest water of each month, not the average — that is what the suit has to cope with.
| January | February | March | April | May | June | July | August | September | October | November | December | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Suit | January: dry | February: dry | March: dry | April: dry | May: dry | June: 7 mm | July: 7 mm | August: 7 mm | September: 7 mm | October: 7 mm | November: dry | December: dry |
- Nov–Maydrysuit
- Jun–Oct7 mm semi-dry
Swell through the year
The rough end of each month — nine days in ten come in under it.
Amber is over 1.5 m.
Tides
Tropical storms
No tropical storm has come within 250 km in 30 years of records. Swell and wind set the season, not cyclones.
- NOAASea surface temperature, from OISST and MUR
- ERA5Wind, waves, rain and air temperature, via Open-Meteo
- OBISMarine species records within 60 km
- IBTrACSTropical cyclone tracks, 1996 to 2025
Cornwall marine life — what you'll see diving
| Species | When | Observed window | Reliability | Evidence | Records |
|---|---|---|---|---|---|
| Common dolphin | All year | Near-guaranteed | 2262 | ||
| Bottlenose dolphin | All year | Near-guaranteed | 1591 | ||
| Basking shark | May–Jul | Near-guaranteed | 4003 | ||
| Ocean sunfish | Jul–Aug | Near-guaranteed | 229 | ||
| Minke whale | Jul–Sep | Near-guaranteed | 201 | ||
| Grey seal | All year | Near-guaranteed | 1092 | ||
| Humpback whale | Dec–Mar | Likely | 53 | ||
| Orca | Mar–May, Jul | Hit-or-miss | 28 | ||
| Blue shark | Jul–Aug | Likely | 14 | ||
| Loggerhead turtle | Jan, Aug–Sep, Nov | Hit-or-miss | 13 | ||
| Harbour seal | Nov–Jan | Hit-or-miss | 8 |
Peak Present
- Observed window
- Months with records. Peak is where most of them fall.
- Reliability
- Near-guaranteed in 60% of surveyed years or more
- Likely 30% to 60%
- Hit-or-miss under 30%
- Evidence
- Years it was seen, out of the years anyone surveyed.
- Records
- OBIS sightings within 60 km.
These are sightings people logged, not a full survey of the reef. A species missing from a month may just mean nobody recorded one.
Diving Cornwall — common questions
- When is the best time to dive Cornwall?
- The best conditions run May to September for the long days — 14.7 hours of light against 10.0. The marine life holds steady all year, so the weather picks the month. The wider season runs April to September.
- When is the diving season in Cornwall?
- The diving season in Cornwall runs April to September, and it is at its best May to September.
- Is the diving in Cornwall good for beginners?
- Yes. It suits Open Water divers, so it works for a first trip after certification.
- How warm is the water in Cornwall?
- Between 10 and 17 °C at the surface across the year, coldest in March and warmest in August. It runs cooler below the thermocline.
- What wetsuit do I need in Cornwall?
- A drysuit covers the coldest water of the year. In the warmest months a 7 mm semi-dry is enough.
- What is the visibility like in Cornwall?
- Roughly 5 to 20 m depending on the month. That is estimated from satellite chlorophyll-a rather than measured in the water.
- What will I see diving Cornwall?
- The most consistently recorded species are Common dolphin (near-guaranteed), Bottlenose dolphin (near-guaranteed) and Basking shark (near-guaranteed), from 9,513 records within 60 km.
- Does Cornwall get tropical storms?
- No. None has passed within 250 km in 30 years of records.
- Is there current in Cornwall?
- The tide rises and falls 4.7 m around the full and new moon, against 2.3 m in between. How much of that becomes current depends on the shape of the channel.
- When should I avoid Cornwall?
- November–February are the weakest months for conditions.
- How do you dive Cornwall?
- Mostly from day boats and the shore. Trips run through the season, Apr–Sep.