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Grand Cayman Bio Bay in May 2027: darkest nights

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

17 pitch-dark nights, 18 dark nights

New moon Thu 6 May · Full moon Thu 20 May

Night by night, May 2027

NightMoon19:0020:30Best
Sat 1 May 19%●●●●●●●●●●20:30
Sun 2 May 12%●●●●●●●●●●20:30
Mon 3 May 6%●●●●●●●●●●20:30
Tue 4 May 2%●●●●●●●●●●20:30
Wed 5 May 0%●●●●●●●●●●20:30
Thu 6 May 1%●●●●●●●●●●20:30
Fri 7 May 4%●●●●●●●●●●20:30
Sat 8 May 10%●●●●●●●●●●20:30
Sun 9 May 17%●●●●●●●●●●20:30
Mon 10 May 27%●●●●●●●●●●20:30
Tue 11 May 38%●●●●●●●●●●20:30
Wed 12 May 50%●●●●●●●●●●20:30
Thu 13 May 62%●●●●●●●●●●20:30
Fri 14 May 73%●●●●●●●●●●20:30
Sat 15 May 82%●●●●●●●●●●20:30
Sun 16 May 90%●●●●●●●●●●20:30
Mon 17 May 95%●●●●●●●●●●20:30
Tue 18 May 99%●●●●●●●●●●19:00
Wed 19 May 100%●●●●●●●●●●19:00
Thu 20 May 99%●●●●●●●●●●19:00
Fri 21 May 96%●●●●●●●●●●20:30
Sat 22 May 92%●●●●●●●●●●20:30
Sun 23 May 86%●●●●●●●●●●20:30
Mon 24 May 79%●●●●●●●●●●20:30
Tue 25 May 71%●●●●●●●●●●20:30
Wed 26 May 62%●●●●●●●●●●20:30
Thu 27 May 53%●●●●●●●●●●20:30
Fri 28 May 43%●●●●●●●●●●20:30
Sat 29 May 33%●●●●●●●●●●20:30
Sun 30 May 24%●●●●●●●●●●20:30
Mon 31 May 16%●●●●●●●●●●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 May 2027?

The darkest nights are Sat 1 May, Sun 2 May, Mon 3 May, Tue 4 May, Wed 5 May, Thu 6 May, Fri 7 May, Sat 8 May, Sun 23 May, Mon 24 May and more. 18 of 31 nights score at least 4 out of 5.

Which nights should I avoid in May 2027?

Avoid the nights around the full moon on Thu 20 May, when moonlight washes out the glow.

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

19:00 is the darker choice on 0 nights; 20:30 is the darker choice on 20 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).