Hawaii Jellyfish Calendar (2026)
Will There Be Jellyfish on Your Trip?
Enter a swim or snorkel date to see if it falls in the predicted box jellyfish window.
Upcoming Box Jellyfish Warning Dates
Box Jellyfish in Hawaii: Pattern, Beaches & Safety Tips
Alatina alata (sometimes still labeled by its older name, Carybdea alata, in older references) is a small, nearly transparent box jellyfish that spends most of its life offshore, then rides the tide onto south-facing, leeward beaches in predictable pulses tied to the lunar cycle.
The Pattern
These jellyfish typically arrive on south-facing shores 8–10 days after each full moon, a pattern tracked for years by local lifeguards and marine researchers. Wind, currents, and tides can still shift exactly where and when they show up, so treat this as a high-probability guide, not a guarantee. Warning signs are also usually posted only at lifeguarded beaches, so an unguarded spot may not have an alert even during a likely window.
Which Beaches
South-facing, leeward Oahu shores are most affected: Waikiki, Ala Moana Beach Park, Hanauma Bay, and Pokai Bay. Maui’s south shore (Kihei, Wailea) occasionally sees them too. Windward shores rarely see box jellyfish, though the Portuguese man-of-war, a different animal entirely, can wash up there after strong trade winds.
If You Get Stung
- Carefully remove any visible tentacles with a towel, card edge, or tweezers — not bare fingers. Tentacles can still sting after they’re off the skin.
- Rinse the area with vinegar, not fresh water, to help stop more venom from releasing.
- Apply heat (a hot but not scalding compress or shower) for about 20 minutes to help with pain.
- Get help from a lifeguard right away, or call 911, for severe reactions or stings near the face or chest — jellyfish stings can occasionally cause anaphylaxis.
How to Avoid Them
- Check this calendar before south or leeward beach days.
- Look for posted warning signs when you arrive — conditions can shift day to day.
- Ask a lifeguard about current jellyfish and man-of-war conditions.
- Swim at guarded beaches whenever possible.
- Stay out of the water if you see jellyfish or man-of-war on the sand.
- Keep children away from beached jellyfish and tentacles.
- On warning days, windward beaches like the North Shore are a safer bet for swimmers against box jellyfish specifically.
Frequently Asked Questions
How does the box jellyfish calendar work?
Hawaiian box jellyfish (Alatina alata) follow a cycle tied to the moon. They typically arrive on south-facing, leeward shores 8–10 days after each full moon, a pattern tracked for years by local lifeguards and marine researchers.
Which Hawaii beaches get box jellyfish?
South-facing, leeward Oahu shores are most affected: Waikiki, Ala Moana Beach Park, Hanauma Bay, and Pokai Bay. Maui’s south shore (Kihei, Wailea) occasionally sees them too. Windward beaches, including the North Shore, rarely see box jellyfish.
What should I do if I get stung by a box jellyfish?
Rinse with vinegar, not fresh water, and remove tentacles with tweezers or a card edge. Apply heat for about 20 minutes. Get help from a lifeguard right away for severe reactions or stings near the face or chest. This is general guidance, not medical advice.
How can I avoid box jellyfish in Hawaii?
Check this calendar before south shore beach days, always swim at guarded beaches, and look for posted warning signs. On warning days, windward beaches are a safer bet for swimmers against box jellyfish specifically.
Is it safe to plan a snorkel day during a warning window?
It’s best to plan your snorkel day around the calendar when possible. Box jellyfish may be present on any day of the year, and conditions can change quickly, so treat these warning dates as a high-probability guide, not a guarantee, and always confirm with a lifeguard before you get in the water.
What’s the difference between a box jellyfish and a Portuguese man-of-war?
They’re different animals entirely. Box jellyfish follow this lunar pattern and mainly affect south-facing, leeward shores. The Portuguese man-of-war is a separate species that can wash up on windward shores after strong onshore winds, unrelated to this monthly pattern.