Month-specific sea-surface temperature · USA

Napili Bay Sea Temperature in September

27.2°C

81.0°F

In September, sea-surface temperature near Napili Bay has a historical monthly average of 27.2°C. This is not the reading for any particular holiday date.

Across 2023–2025, the lowest and highest yearly September monthly means were 26.9–27.6°C. These are not daily extremes.

Previous month

August · 27.0°C

Change into September: +0.2°C

Next month

October · 27.0°C

Change into next month: -0.2°C

Can you swim or snorkel in Napili Bay in September?

At 27.2°C our temperature-only guide describes the water as warm water. Comfort depends on your cold tolerance, immersion time and wind. A historical average cannot determine whether conditions are safe on any given day.

Do you need a wetsuit?

Most people are comfortable in swimwear or a light rash guard.

Which beach should you choose?

Look for a beach sheltered from the actual forecast waves and wind on your visit. Exposure, currents and entry conditions vary even where water temperatures are similar. Follow local warnings.

Check the current waves, wind and snorkeling forecast →

A live forecast does not predict a future September. Check again close to your trip.

Waves and wind: recorded-model conditions for September

These figures come from a separately modelled, date-specific wind/wave backfill, not the NOAA SST series. A single observed season is not a climatological likelihood or a guarantee of safe conditions.

Compare nearby coasts with their own evidence

Coast	Morning	Afternoon	Period
Maui	19%	19%	Sep 2026

A “calm hour” meets fixed modelled wave/wind thresholds; neither visibility nor local currents, entry conditions or actual beach safety is measured here. Periods may differ by coast.

Nearby places in September

Comparable historical averages from independent marine grid cells. Warmer water does not imply safe snorkeling.

Napili Bay Sea Temperature: All 12 Months

Choose a month for available historical evidence, month comparisons and swim guidance. Missing history is clearly marked and never presented as a long-term normal.

January 25.3°C February 24.6°C March 24.7°C April 25.2°C May 25.6°C June 26.2°C July 26.6°C August 27.0°C September 27.2°C October 27.0°C November 26.4°C December 25.8°C

Data source and limitations

Source: Open-Meteo Marine API, MeteoFrance sea-surface temperature; 2023–2025. Marine model grid near 21.00, -156.67. Based on 3 yearly monthly means and 2160 recorded samples. Source methodology.

Modelled sea-surface temperatures do not establish underwater visibility, wildlife, calm currents or safe entry.