Costa Rica

Best Time to Dive in Cocos Island

5.56°N 87.03°W

Go June to November for scalloped hammerhead. 10 days a month of heavy rain then — December to March is calmer, but the animals have gone.

Best time
Jun–Nov
Water
27–30 °C
Visibility
20–35 m
Dived from
liveaboard
Tidal range
1.4–2.6 m
Species logged
8

Worth knowing: 10 days a month of heavy rain.

Where it is

Costa Rica
250 kmN

888 km across · coastline from Natural Earth 10m

Diving in Cocos Island — monthly breakdown

Best months at this destination

A year of scuba diving conditions at a glance. Hover a month to isolate it.

Month by month conditions, water temperature, visibility and marine life
JanuaryFebruaryMarchAprilMayJuneJulyAugustSeptemberOctoberNovemberDecember
ConditionsPoorPoorPoorPoorPoorExcellentExcellentExcellentExcellentExcellentExcellentPoor
Water temp (°C)282930302928282828272728
Visibility (m)20–3020–3020–3020–3020–3020–3020–3020–3020–3020–3020–3025–35
Marine lifeQuietQuietQuietQuietQuietBusyBusyBusyBusyBusyBusyQuiet
Best timePeakPeakPeakPeakPeakPeak
Excellent Good Moderate PoorPeak season Jun–Nov

Long-term averages, 2016–2025. Visibility is estimated from satellite chlorophyll-a. Water temperature is the surface mean; it is cooler at depth.

The Cocos Island diving season

2 seasons

June to November · Peak season

6 months
Water temperature
27–28 °C
Visibility
20–30 m
Rain
26 days a month

Diving conditionsThe wind is up.

Marine lifeScalloped hammerhead (likely), Oceanic manta (hit-or-miss), Tiger shark (hit-or-miss) peak at Cocos Island in these months.

December to May · Off season

6 months
Water temperature
28–30 °C
Visibility
20–30 m
Rain
23 days a month

Diving conditionsThe wind eases.

Marine lifePelagic thresher (hit-or-miss), Scalloped hammerhead (likely), Oceanic manta (hit-or-miss), Tiger shark (hit-or-miss) peak at Cocos Island in these months.

  • Spring tides run 2.6 m against 1.4 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.

Cocos Island water temperature and weather

483 underwater observation records · 16 surveyed years of ocean data · 10 years of sea temperature

Water & weather

Cocos Island water temperature by month

The dashed line is the monthly average. Eight days in ten fall inside the band.

262728293031JanFebMarAprMayJunJulAugSepOctNovDecSea temperature (°C)

10th to 90th percentile rangemonthly mean

Rarely
rough enough to cancel

Seas top 2.5 m on under 1% of days. Enough to cancel a liveaboard crossing

0
blowy days a month

Gusts over 40 km/h, about where a day boat stays in port

25
wet days a month

9 of them bring heavy rain

Monthly sea state, wind, rain, air temperature and daylight
MonthSwellGusts over 40 km/hWet daysHeavy rainAirDaylight
January1.8 m0%23527 °C11.7 h
February1.7 m0%16228 °C11.8 h
March1.7 m0%21428 °C12.0 h
April1.8 m0%271228 °C12.1 h
May2.1 m1%281728 °C12.3 h
June2.1 m1%271227 °C12.3 h
July2.2 m0%291327 °C12.3 h
August2.1 m1%281227 °C12.2 h
September2.2 m0%281026 °C12.0 h
October2.1 m1%23726 °C11.9 h
November2.3 m1%24726 °C11.7 h
December1.8 m0%25627 °C11.7 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.

Conditions by week, four weeks per month
Week 1January week 1: PoorFebruary week 1: PoorMarch week 1: PoorApril week 1: ModerateMay week 1: ModerateJune week 1: ExcellentJuly week 1: ExcellentAugust week 1: ExcellentSeptember week 1: ExcellentOctober week 1: GoodNovember week 1: ExcellentDecember week 1: Moderate
Week 2January week 2: PoorFebruary week 2: PoorMarch week 2: PoorApril week 2: ModerateMay week 2: ModerateJune week 2: ExcellentJuly week 2: ExcellentAugust week 2: ExcellentSeptember week 2: ExcellentOctober week 2: ExcellentNovember week 2: ExcellentDecember week 2: Poor
Week 3January week 3: PoorFebruary week 3: PoorMarch week 3: PoorApril week 3: ModerateMay week 3: PoorJune week 3: ExcellentJuly week 3: ExcellentAugust week 3: GoodSeptember week 3: ExcellentOctober week 3: ExcellentNovember week 3: ExcellentDecember week 3: Poor
Week 4January week 4: PoorFebruary week 4: PoorMarch week 4: PoorApril week 4: ModerateMay week 4: PoorJune week 4: ExcellentJuly week 4: ExcellentAugust week 4: ExcellentSeptember week 4: ExcellentOctober week 4: ExcellentNovember week 4: ExcellentDecember week 4: Poor
Excellent Good Moderate PoorBest week to go: fourth of November

November, week by week

WeekConditionsWaterSwellWindRain chance
Week 1Excellent27 °C2.3 m28 km/h77%
Week 2Excellent27 °C2.3 m27 km/h79%
Week 3Excellent27 °C2.1 m27 km/h84%
Week 4Excellent27 °C2.0 m26 km/h83%

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.

Wetsuit thickness by month
JanuaryFebruaryMarchAprilMayJuneJulyAugustSeptemberOctoberNovemberDecember
SuitJanuary: skinFebruary: skinMarch: skinApril: skinMay: skinJune: skinJuly: skinAugust: skinSeptember: skinOctober: 3 mmNovember: 3 mmDecember: 3 mm
  • Jan–Sepskin or 3 mm shorty
  • Oct–Dec3 mm full suit

Swell through the year

The rough end of each month — nine days in ten come in under it.

JanJanuary: 1.8 metresFebFebruary: 1.7 metresMarMarch: 1.7 metresAprApril: 1.8 metresMayMay: 2.1 metresJunJune: 2.1 metresJulJuly: 2.2 metresAugAugust: 2.1 metresSepSeptember: 2.2 metresOctOctober: 2.1 metresNovNovember: 2.3 metresDecDecember: 1.8 metres

Amber is over 2.5 m.

Tides

springs 2.8 mneaps 1.5 mneapsone lunar month
Daily tidal range across one lunar month.

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

Cocos Island marine life — what you'll see diving

483 records within 60 km
SpeciesWhenObserved windowReliabilityEvidenceRecords
Bottlenose dolphinSep–Oct, DecLikely
6/16
77
Silky sharkDec–JanHit-or-miss
2/16
23
Pelagic thresherDecHit-or-miss
1/16
17
Whitetip reef sharkJan–Feb, Jun–JulLikely
9/16
141
Scalloped hammerheadJan, Aug–SepLikely
8/16
130
Bigeye trevallyJan–Feb, SepLikely
7/16
32
Oceanic mantaJun–Jul, DecHit-or-miss
3/16
26
Tiger sharkJan, OctHit-or-miss
3/16
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 Cocos Island — common questions

When is the best time to dive Cocos Island?
Go June to November for scalloped hammerhead. 10 days a month of heavy rain then — December to March is calmer, but the animals have gone.
When is the diving season in Cocos Island?
Conditions are good December to March, but most divers come June to November for the marine life.
Is the diving in Cocos Island good for beginners?
Not really. It is for experienced divers, so it is not a place to learn or to make your first dives after certification.
How warm is the water in Cocos Island?
Between 27 and 30 °C at the surface across the year, coldest in November and warmest in March. It runs cooler below the thermocline.
What wetsuit do I need in Cocos Island?
A 3 mm full suit covers the coldest water of the year. In the warmest months a skin or 3 mm shorty is enough.
What is the visibility like in Cocos Island?
Roughly 20 to 35 m depending on the month. That is estimated from satellite chlorophyll-a rather than measured in the water.
What will I see diving Cocos Island?
The most consistently recorded species are Bottlenose dolphin (likely), Silky shark (hit-or-miss) and Pelagic thresher (hit-or-miss), from 483 records within 60 km.
Does Cocos Island get tropical storms?
No. None has passed within 250 km in 30 years of records.
Is there current in Cocos Island?
The tide rises and falls 2.6 m around the full and new moon, against 1.4 m in between. How much of that becomes current depends on the shape of the channel.
When should I avoid Cocos Island?
April–May are the weakest months for conditions.
How do you dive Cocos Island?
Mostly from liveaboards. Trips run through the season, Dec–Mar.