How trade winds affect rainfall, runoff, and beach water quality across all islands
Hawaiiʻs trade winds blow consistently from the northeast. The windward side of each island faces into these winds and receives significantly more rainfall. The leeward side is sheltered and stays much drier. This fundamental difference shapes everything from vegetation to water quality.
Windward beaches (like Kailua and Waimanalo on Oʻahu, or Hilo on the Big Island) receive 2-4 times more rainfall than leeward beaches. More rain means more runoff carrying bacteria from land into the ocean. After storms, windward beaches take longer to recover.
Leeward beaches (like Ko Olina and Makaha on Oʻahu, or Kohala Coast on the Big Island) get far less rain. With less runoff, these beaches generally have better water quality. However, when Kona storms bring rain from the south, leeward beaches that never see advisories can suddenly get them.
If you are visiting during wet season (October through March), leeward beaches are more likely to have clear water quality. During dry season, both sides are generally favorable. After any rain event, check the live advisory status for the specific beach you plan to visit.
Oʻahu: Windward (Kailua, Waimanalo, Kahana Bay) vs. Leeward (Ko Olina, Makaha, Ewa). Maui: Windward (Baldwin Beach, Hookipa) vs. Leeward (Wailea, Kaʻanapali). Big Island: Windward (Hilo, Richardson) vs. Leeward (Kohala, Kona). Kauaʻi: Windward (North Shore, Hanalei) vs. Leeward (Poipu, West Side).
Free alerts when water quality changes at your beach — brown water advisories, bacteria warnings, and all-clear notices.
No spam. Just safety alerts for your trip.
500+ beaches and 25+ hotels across all 6 islands
Safe to Swim Hawaii provides water quality information based on publicly available DOH data and seasonal patterns. This is not medical or safety advice. Always check current conditions, obey posted signs, and use your own judgment before entering the ocean. Privacy Policy
⚠️ 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 geographic analysis. 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. 🤙