Scalloped Hammerhead Shark Sphyrna Lewini (226845659)
Scalloped Hammerhead Shark Sphyrna Lewini (226845659) by Kris Mikael Krister, CC BY 3.0, via Wikimedia Commons

Costa Rica · Eastern Pacific

Best time to dive Cocos Island

Liveaboard-only (~36–40 h crossing). Hammerheads year-round; the wet season (June–November) brings bigger schools but rough crossings and rain, while December–May is calmer with smaller, steadier groups.

Peak season: June–November

Best upcoming months:7.7November 20277.6December 20277.5August 2027
Book a Cocos Island LiveaboardUpcoming departures on Divebooker

Overall diving, month by month

Balanced scoring · forecasts include the 2026/27 El Niño outlook

0510Nov 2026: 6.5 (Good)6.5Nov2026Dec 2026: 6.2 (Good)6.2DecJan 2027: 5.9 (Good)5.9Jan2027Feb 2027: 6.0 (Good)6.0FebMar 2027: 6.3 (Good)6.3MarApr 2027: 6.5 (Good)6.5AprMay 2027: 6.8 (Good)6.8MayJun 2027: 7.1 (Great)7.1JunJul 2027: 7.2 (Great)7.2JulAug 2027: 7.5 (Great)7.5AugSep 2027: 7.5 (Great)7.5SepOct 2027: 7.5 (Great)7.5OctNov 2027: 7.7 (Great)7.7NovDec 2027: 7.6 (Great)7.6Dec

Confidence: Nov medium · Dec medium · Jan low · Feb low · Mar low · Apr low · May low · Jun low · Jul medium · Aug low · Sep low · Oct low · Nov low · Dec low

What's good when

Each attribute scored 0–10 for every month

Nov2026DecJan2027FebMarAprMayJunJulAugSepOctNovDec
Pelagic & big animals8766778991010101010
Macro life33333333333333
Coral & reef health22222222222233
Visibility67788876666667
Water temperature101010101010109988888
Weather & sea state67677765555567
Operations & access99999999999999

Climate outlook

How this year's forecast differs from a typical year

  • Water temperature +2.9 °C · El Niño warms surface water and suppresses upwelling (Nov 2026 – December 2027)
  • Pelagic & big animals -2.3 · Warm water pushes hammerheads deep and thins pelagic action (La Niña helps) (Nov 2026 – December 2027)
  • Coral & reef health -1.6 · Marine heatwave stress on reefs and reef fish (Nov 2026 – December 2027)
  • Weather & sea state -1.2 · El Niño brings heavy rain in the warm season (Jan 2027 – May 2027)

Water temperature & visibility

MonthWaterVisibility
November 202629.8 °C (86 °F)15–20 m
December 202629.9 °C (86 °F)15–25 m
January 202729.6 °C (85 °F)15–25 m
February 202729.2 °C (85 °F)20–30 m
March 202729.2 °C (85 °F)20–30 m
April 202729.1 °C (84 °F)20–30 m
May 202728.7 °C (84 °F)15–25 m
June 202727.7 °C (82 °F)12–20 m
July 202727.0 °C (81 °F)12–20 m
August 202726.3 °C (79 °F)12–20 m
September 202726.1 °C (79 °F)12–20 m
October 202726.0 °C (79 °F)12–20 m
November 202726.3 °C (79 °F)15–20 m
December 202726.3 °C (79 °F)15–25 m

Marine life calendar

JanFebMarAprMayJunJulAugSepOctNovDec
scalloped hammerhead●●●●●PeakPeakPeakPeakPeakPeak●
whitetip reef shark●●●●●●●●●●●●
marble ray●●●●●●●●●●●●
silky shark●●●●●●●●●●●●

Peak = best odds · ● = regularly seen · blank = unlikely. Calendar months, every year.

About the diving

Difficulty
Expert
Current strength
5 / 5
Luxury level
3 / 5
Typical depth
15–35 m
Max depth of interest
40 m
Dive styles
Liveaboard
Suggested certification
Advanced Open Water + experience in strong currents
Nearest airport
SJO
Snorkelling
Limited
Known for
scalloped hammerhead, whitetip reef shark, silky shark, marble ray

Famous sites: Bajo Alcyone · Dirty Rock · Manuelita · Dos Amigos

Season notes & sources

  • Liveaboard-only (~36–40 h crossing). Hammerheads year-round; the wet season (June–November) brings bigger schools but rough crossings and rain, while December–May is calmer with smaller, steadier groups.
  • Divers reported fewer hammerheads and mantas during the 1997 El Niño, which reached from Galápagos to Cocos.

Sources