Beach & water quality guide — which coast to visit, top beaches, and what to expect
The Kohala Coast (Waikoloa, Mauna Lani) stays dry and calm in winter, making it the best swimming area. The Kona Coast is moderate with occasional rain. Hilo and the Hamakua Coast receive very heavy rainfall (10+ inches/month) with elevated bacteria risk near stream mouths. The Big Island’s size creates dramatically different microclimates — Kona side and Hilo side can have completely opposite weather on the same day.
These beaches have elevated risk factors this month. Check current conditions before you go.
The Big Island has the most dramatic weather variation of any Hawaiian island. The Kohala and Kona coasts recover within 24 hours because they get so little rain. The Hilo side can take 72+ hours and receives 10x more rainfall. Rainy-day alternatives: Hawaiʻi Volcanoes National Park (lava tubes are underground), Kona coffee farm tours, Mauna Kea summit (above the clouds), Hilo Farmers Market.
Whale watching season peaks January through March off the Kohala Coast. The Kona Coffee Cultural Festival (November) celebrates Big Island coffee heritage. Manta ray night snorkels run year-round but winter’s calmer plankton patterns often bring larger mantas.
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Big Island in December is in the wet season with higher rainfall and bigger surf on exposed coasts. Average rainfall is 3 inches (on the dry side), water temperature is 74–76°F, and advisory risk is moderate–high. Wet season — conditions vary by coast. Choose the dry/calm side of the island.
In December, Big Island's Kohala Coast (Waikoloa, Mauna Lani resorts) and Kona Coast offer the calmest conditions. The Hilo side gets very heavy rainfall with elevated bacteria risk.
Yes, it can rain on Big Island in December, but conditions vary dramatically by location. The dry/leeward side averages about 3 inches for the month, while the wet/windward side can receive 5-10x that amount. Winter months see more rainfall overall, which can elevate bacteria levels near stream mouths.
The best beaches on Big Island in December include Hapuna Beach, Mauna Kea Beach, A-Bay (Anaehoomalu). These are recommended for December because they are on the calmer, drier side of the island away from heavy surf and rainfall.
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⚠️ Important Disclaimer
Safe to Swim Hawaii is an independent passion project — not affiliated with the Hawaii Department of Health or any government agency. Water quality ratings are estimates based on publicly available testing data and seasonal patterns. They are not real-time measurements and may not reflect current conditions.
Always verify current water quality conditions with the Hawaii DOH Clean Water Branch before entering the water.
When in doubt, don't go out. 🤙