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Planning Tools

Jellyfish Calendar

Predicted box jellyfish watch windows for Hawaii's south-facing beaches — calculated from the lunar cycle.

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By John C. Derrick & Tori C. Derrick

Check Your Beach Date

Enter a swim or snorkel date to see whether it falls inside the predicted Box Jellyfish Watch window.

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    How It Works

    The Pattern

    Hawaiian box jellyfish (Alatina alata) presence can follow a lunar pattern. Expected influxes are often described around 8 to 10 days after a full moon; HawaiiGuide extends the planning watch through day 12 as a cautious buffer. It cannot confirm sightings at a particular beach.

    Which Beaches

    South-facing shores are most affected: Waikiki, Ala Moana Beach Park, Hanauma Bay, and Pokāī Bay on Oahu. Maui south shore beaches (Kīhei, Wailea) occasionally see them too. North shores are rarely affected.

    If You Get Stung

    Get out of the water and seek a lifeguard or medical help. Do not rub the affected area. Call 911 for difficulty breathing, signs of shock, or severe pain. Read our sting first-aid guidance and sources and the Red Cross's first-aid guide.

    Use the Watch

    Check the calendar before planning a south-shore beach day. During a watch window, look for posted beach warnings and ask a lifeguard about current conditions before entering the water.

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    Snorkelers on a Hawaii beach checking ocean conditions before entering the water

    Planning a Snorkel Day?

    The calendar is one layer of beach-day planning. Before you get in the water, check surf, tide, wind, posted signs, and lifeguard guidance too.

    Check the Ocean Report