Hawaii's rainy season, Kona storms, and how rain affects water quality for beach swimmers.
Hawaii doesn't have a traditional monsoon in the Southeast Asian sense, but it has a distinct wet season (November–March) and dry season (April–October). The wet season brings frontal storms, "Kona storms" (low-pressure systems from the south), and atmospheric river events that can dump inches of rain in hours. These events significantly impact beach water quality.
For beach safety and water quality, understanding Hawaii's seasonal weather patterns is essential. Rain events trigger bacteria spikes at monitored beaches and pose flash flood and tsunami risk at coastal areas.
Kauaʻi is the wettest of the main Hawaiian Islands year-round. The North Shore (Hanalei, Haʻena) can be affected by rain at almost any time of year. During wet season, flash floods are a real danger — the Hanalei Valley has been subject to road closures. Water quality at Kauaʻi beaches degrades significantly after rain. Leeward beaches like Poʻipū fare better. After any significant storm, wait 72+ hours.
East Maui (Hana area) is extremely wet year-round. West Maui (Kaʻanapali, Lahaina) is drier but affected by West Maui Mountain storms in winter. South Maui (Wailea, Makena) is the driest area and maintains better beach conditions through wet season. Water quality at Wailea is among the most resilient in Hawaii during wet season.
Oʻahu's urban development means rain events translate directly into bacteria spikes at beaches — especially near the Ala Wai Canal (Waikiki), Kailua Bay (windward), and the North Shore. The Koʻolau Mountains on the windward side receive heavy rainfall that drains through urban Kaneohe and Kailua. Leeward beaches (Ko Olina, Makaha) recover more quickly. DOH advisories are most frequent on Oʻahu after wet season storms.
The Big Island has the most extreme rainfall variation of any Hawaiian island. Hilo averages 130+ inches/year; Kailua-Kona averages 25 inches/year. The dry Kohala Coast resort beaches (Mauna Kea, Mauna Lani, Hilton Waikoloa) maintain excellent water quality through wet season. East and Puna Coast beaches face elevated runoff risk after rain.
"Kona storms" are low-pressure systems that approach Hawaii from the south, bringing rain to typically dry leeward shores that are normally protected from trade-wind rainfall. These storms flip the normal rainfall pattern, causing some of the worst water quality events of the year at leeward resort beaches.
When a Kona storm is forecast, prepare for degraded ocean conditions at all Hawaii beaches for 48–72+ hours. Check NWS Pacific Region for storm forecasts before any beach visit.
After heavy rain anywhere in Hawaii, the Department of Health recommends staying out of the ocean for at least 72 hours. This applies across all islands and all seasons. If the water appears brown or murky, do not enter regardless of how much time has passed since rain.
If you're visiting Hawaii during wet season (Nov–Mar), these beach areas tend to have the most resilient water quality:
Free alerts when water quality changes at your beach — storm advisories, bacteria warnings, and all-clear notices.
No spam. Just safety alerts for your trip.
100+ beaches and 25+ hotels across all 6 islands
⚠️ Important Disclaimer
Safe to Swim Hawaii is an independent passion project — not affiliated with the Hawaii Department of Health or any government agency. Weather and seasonal information on this page is general in nature. Hawaii weather is highly variable — always check current NWS forecasts and DOH advisories before any beach visit.
Always verify current water quality with the Hawaii Department of Health Clean Water Branch before entering the water.
When in doubt, don't go out.