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Grand Cayman Bio Bay in December 2026: darkest nights

Boat tours leave from Rum Point and Kaibo. Operators cancel on bright full-moon nights. Year-round.

18 pitch-dark nights, 19 dark nights

New moon Tue 8 Dec · Full moon Wed 23 Dec

Night by night, December 2026

NightMoon19:0020:30Best
Tue 1 Dec 41%●●●●●●●●●●20:30
Wed 2 Dec 30%●●●●●●●●●●20:30
Thu 3 Dec 21%●●●●●●●●●●20:30
Fri 4 Dec 13%●●●●●●●●●●20:30
Sat 5 Dec 7%●●●●●●●●●●20:30
Sun 6 Dec 3%●●●●●●●●●●20:30
Mon 7 Dec 1%●●●●●●●●●●20:30
Tue 8 Dec 0%●●●●●●●●●●20:30
Wed 9 Dec 1%●●●●●●●●●●20:30
Thu 10 Dec 4%●●●●●●●●●●20:30
Fri 11 Dec 9%●●●●●●●●●●20:30
Sat 12 Dec 15%●●●●●●●●●●20:30
Sun 13 Dec 22%●●●●●●●●●●20:30
Mon 14 Dec 31%●●●●●●●●●●20:30
Tue 15 Dec 41%●●●●●●●●●●20:30
Wed 16 Dec 51%●●●●●●●●●●20:30
Thu 17 Dec 61%●●●●●●●●●●20:30
Fri 18 Dec 72%●●●●●●●●●●20:30
Sat 19 Dec 81%●●●●●●●●●●20:30
Sun 20 Dec 89%●●●●●●●●●●20:30
Mon 21 Dec 95%●●●●●●●●●●20:30
Tue 22 Dec 99%●●●●●●●●●●19:00
Wed 23 Dec 100%●●●●●●●●●●19:00
Thu 24 Dec 98%●●●●●●●●●●19:00
Fri 25 Dec 94%●●●●●●●●●●19:00
Sat 26 Dec 87%●●●●●●●●●●19:00
Sun 27 Dec 78%●●●●●●●●●●19:00
Mon 28 Dec 68%●●●●●●●●●●20:30
Tue 29 Dec 58%●●●●●●●●●●20:30
Wed 30 Dec 47%●●●●●●●●●●20:30
Thu 31 Dec 37%●●●●●●●●●●20:30

Check one night in detail Grand Cayman Bio Bay tours

Questions

What are the best nights to see the bioluminescence at Grand Cayman Bio Bay in December 2026?

The darkest nights are Tue 1 Dec, Wed 2 Dec, Thu 3 Dec, Fri 4 Dec, Sat 5 Dec, Sun 6 Dec, Mon 7 Dec, Tue 8 Dec, Wed 9 Dec, Thu 10 Dec and more. 19 of 31 nights score at least 4 out of 5.

Which nights should I avoid in December 2026?

Avoid the nights around the full moon on Wed 23 Dec, when moonlight washes out the glow.

19:00 or 20:30: which Grand Cayman Bio Bay tour is darker in December?

19:00 is the darker choice on 3 nights; 20:30 is the darker choice on 18 nights.

Grand Cayman Bio Bay darkness by month

Darkness score 1-5 per tour slot from twilight and moonlight. Weather and plankton health are not included. Times are local (America/Cayman).