Does it rain at Hanalei Bay in September?

September is part of the drier season at Hanalei Bay. While the north shore still receives more rain than south Kauai, conditions are significantly better than winter. The 360+ cesspools in the watershed still contribute to bacteria near river mouths even in dry months.

Is September a good time to swim at Hanalei Bay?

September at Hanalei Bay has moderate bacteria risk based on historical patterns. Summer brings the calmest conditions to Hanalei Bay. Conditions in september are variable. Monitor the live advisory status above, check recent rainfall, and use the 72-hour rain rule before swimming.

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Kauaʻi · North Shore

Hanalei Bay Water Quality in September

Q: What is Hanalei Bay water quality like in September?

September at Hanalei Bay is typically characterized by moderate bacteria risk based on seasonal rainfall patterns. September stays relatively dry at Hanalei. Even in the dry season, Hanalei Bay's persistent cesspool contamination maintains elevated bacteria near river mouths. Summer conditions are the best of the year, but swimming near rivers is still inadvisable.

What to expect for water quality, rainfall, and ocean conditions

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September Conditions at Hanalei Bay

September Advisory Risk Moderate

Even in the dry season, Hanalei Bay's persistent cesspool contamination maintains elevated bacteria near river mouths. Summer conditions are the best of the year, but swimming near rivers is still inadvisable.

🌧️ Rainfall & Runoff

September stays relatively dry at Hanalei. The bay maintains good conditions. Some early-season north swell can arrive late in the month, beginning the transformation from calm summer bay to winter surf break.

🌊 Ocean Conditions

Summer brings the calmest conditions to Hanalei Bay. The ocean is flat, warm (79-80°F), and suitable for swimming, kayaking, and SUP. The crescent bay is one of Hawaii's most beautiful settings in calm conditions.

👥 Crowd Levels

Moderate to low. Fall shoulder season offers fewer tourists while conditions remain good. This is one of the best value periods for visiting Hawaii.

📌 September Notes

•Hanalei Bay has been on the EPA impaired waters list since 2004 due to chronic bacteria contamination. Over 360 cesspools in the watershed leak untreated sewage into the four rivers feeding the bay. Avoid swimming near river mouths, especially after rain.

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If It Looks Brown, Don't Swim

Never enter the ocean when the water appears brown or murky, even if no advisory is posted. Hawaii is often slow to test beaches and update advisories — not every beach is monitored. After heavy rain, wait at least 72 hours and until the water clears before swimming.

Learn more about brown water advisories →

⚠️ The 72-Hour Rain Rule

The Hawaii Department of Health recommends staying out of the ocean for at least 72 hours after heavy rain. In september, rainfall is less frequent but individual storms can still produce contaminated runoff.

Book Tours & Activities

When conditions are clear, Hanalei Bay has excellent ocean activities. Check the water quality above, then book with confidence.

⛳ Hanalei Bay Kayak Tour

Guided kayak and snorkel tour of Hanalei Bay with mountain and waterfall views.

Viator

🏄 Na Pali Coast & Hanalei Tour

Full-day tour of Kauai's legendary north shore including Hanalei Bay and Na Pali views.

GetYourGuide

Tours listed via Viator and GetYourGuide. Safe to Swim Hawaii may earn a commission if you book, at no extra cost to you.

Hanalei Bay — Other Months

Hanalei Bay in January→ Hanalei Bay in February→ Hanalei Bay in March→ Hanalei Bay in April→ Hanalei Bay in May→ Hanalei Bay in June→ Hanalei Bay in July→ Hanalei Bay in August→ Hanalei Bay in October→ Hanalei Bay in November→ Hanalei Bay in December→

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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