Month-specific sea-surface temperature · New Zealand
Bay of Islands Sea Temperature in September
15.6°C
60.1°F
In September, sea-surface temperature near Bay of Islands has a historical monthly average of 15.6°C. This is not the reading for any particular holiday date.
Across 2023–2025, the lowest and highest yearly September monthly means were 15.2–16.0°C. These are not daily extremes.
Previous month
August · 15.3°C
Change into September: +0.3°C
Next month
October · 15.8°C
Change into next month: +0.2°C
Can you swim or snorkel in Bay of Islands in September?
At 15.6°C our temperature-only guide describes the water as cold 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?
Use a full 3-5 mm wetsuit and keep the session within your cold-water experience.
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 |
|---|---|---|---|
| Goat Island | 35% | 25% | 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.
- Poor Knights Islands 15.8°C
- Goat Island 15.0°C
Data source and limitations
Source: Open-Meteo Marine API, MeteoFrance sea-surface temperature; 2023–2025. Marine model grid near -35.22, 174.09. 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.