Big Island Box Jellyfish Calendar

The predictable window when box jellyfish reach south and leeward shores.

Hawaii's box jellyfish arrive on a lunar clock. Roughly 8 to 10 days after each full moon, they drift into south-facing and leeward shores to spawn, then thin out again. It is one of the more predictable things in the ocean here, which is why lifeguards post signs and some south-shore beaches close swim zones on those days.

The windows below are computed from the full moon. Treat them as a heads-up for planning a south-shore swim, not a guarantee: numbers vary year to year, and a sting can happen any day.

Upcoming windows

  • Aug 6 – Aug 8Full moon July 29
  • Sep 4 – Sep 6Full moon August 27
  • Oct 4 – Oct 6Full moon September 26
  • Nov 2 – Nov 4Full moon October 25
  • Dec 2 – Dec 4Full moon November 24
  • Dec 31 – Jan 2Full moon December 23

If you get stung

  • Get out of the water and don't rub the area. Pick off any tentacles with a gloved hand or a stick, not bare fingers.
  • Rinse with vinegar if it's on hand; many Hawaii beaches keep it at the lifeguard stand. Then use heat, a hot pack or hot water as you can tolerate, for the pain.
  • Watch for a whole-body reaction, trouble breathing, or chest pain, and call 911 if any of that shows. When in doubt, tell a lifeguard, they deal with this constantly.

Check today's Big Island surf and advisories →

Timing is computed from the lunar cycle and reflects the well-documented Waikiki pattern. First-aid guidance follows standard Hawaii lifeguard practice; it is not medical advice.