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Jellyfish Calendar

Box jellyfish warning dates for Hawaii's south-facing beaches — calculated from the lunar cycle.

We may link to trusted Hawaiʻi resources at no extra cost to you.

Check Your Beach Date

Enter a swim or snorkel date to see whether it falls inside the predicted box jellyfish warning window.

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Warning (active today) Warning window Today Full moon

Upcoming Warning Dates

    How It Works

    The Pattern

    Hawaiian box jellyfish (Alatina alata) follow a predictable cycle tied to the moon. They arrive on south-facing shores approximately 8 to 10 days after each full moon, almost like clockwork.

    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

    Rinse with vinegar (not fresh water). Remove tentacles with tweezers or a credit card edge. Apply heat (hot shower or hot pack, not scalding) for 20 minutes. Seek medical attention for severe reactions, difficulty breathing, or stings to the face or chest.

    How to Avoid Them

    Check this calendar before planning south shore beach days. On warning days, swim at north-facing or west-facing beaches instead. Look for purple warning signs posted by lifeguards at affected beaches.

    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

    More Ocean Planning Resources

    Ocean Report Live surf, tides, water temperature, wind, and coastal conditions. Jellyfish First Aid Box jellyfish vs. man-o'-war, sting care, and when to get help. Beach Flag Warnings What green, yellow, red, double-red, and purple flags mean. Summer Ocean Safety Jellyfish windows, south swells, currents, and seasonal hazards. Beach Finder Pick beaches by island, activity, crowd level, and conditions fit. Best Snorkeling Spots Island-by-island snorkel locations and calmer-water planning.
    Ocean Report — Surf forecast, tides & water temps Whale Season — Are humpbacks here right now? Sunrise & Sunset — Today's times & golden hour Live Weather — 7-day forecast & microclimate data
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    Hawaiʻi Weather Forecast

    Today’s Weather Brief · AI-voiced · ~45s

    Updated

    0:00 0:45
    Read the transcript

    Partly cloudy on the windward side, mostly sunny on the leeward side. Trade winds are strong and will stay that way through Wednesday, bringing passing showers to windward slopes.

    Surf builds this weekend—a south swell is coming in and could reach warning levels on south-facing beaches by Saturday and Sunday. Winds ease late Thursday, and you'll see more organized showers Friday through Saturday as a system moves nearby. Small Craft Advisory is up through Wednesday evening, so water's rough if you're thinking about boats.

    Stick to leeward beaches and the sunny side through Wednesday. Save your snorkeling for after the weekend swell passes.

    AI summary · verify with NWS before heading out

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    Oahu microclimate guide → All-island forecast hub →
    Also today Ocean & surf Sunrise & sunset Jellyfish calendar
    Temperature
    Weather data by Open-Meteo.com