Rottnest Island Water Temperature
Updated Tue 14:52 (Australia/Brisbane)
Australia · Forecast updated Sep 22, 2026, 14:52 UTC · refresh delayed
Current Sea Temperature
18.9°C
66.0°F
Cool water
Valid Sep 22, 2026, 14:52 (Australia/Brisbane). Source: stored Open-Meteo marine forecast. Temperature is not a safety rating or snorkel score.
Versus this month's average
0.4°C above
The typical September average is 18.5°C (65.3°F) from the historical baseline.
Recent trend
Warming by 0.4°C
Seven-day average: 18.8°C, versus 18.4°C in the prior seven days.
What to wear
Cool water
A 3 mm shorty or full wetsuit will make longer snorkels more comfortable.
Cold tolerance varies. Wind, session length, sunshine, and exertion also affect comfort; temperature alone does not describe sea conditions or replace the snorkel forecast.
Typical Sea Temperature Over the Year
In the historical baseline for Rottnest Island, typical monthly averages range from about 18.5°C (65.3°F) in September to 22.6°C (72.7°F) in March.
Over the past 30 days, the average sea temperature in Rottnest Island has been 18.5°C.
Historical baseline (full year)
Southern Hemisphere. Summer is generally December–February; winter is June–August.
Typical monthly sea-surface temperature near Rottnest Island, calculated from hourly observations for 2023–2025. This is not this site's forecast archive.
| Month | Typical range | Average |
|---|---|---|
| January | 21.8–22.9°C | 22.5°C / 72.5°F |
| February | 22.3–22.5°C | 22.4°C / 72.3°F |
| March | 21.9–23.3°C | 22.6°C / 72.7°F |
| April | 21.5–23.4°C | 22.4°C / 72.3°F |
| May | 21.1–22.7°C | 22.1°C / 71.8°F |
| June | 19.7–21.3°C | 20.7°C / 69.3°F |
| July | 18.4–19.9°C | 19.3°C / 66.7°F |
| August | 18.2–19.1°C | 18.7°C / 65.7°F |
| September | 18.0–18.8°C | 18.5°C / 65.3°F |
| October | 18.9–19.2°C | 19.1°C / 66.4°F |
| November | 19.6–20.1°C | 19.9°C / 67.8°F |
| December | 21.3–22.0°C | 21.6°C / 70.9°F |
Source: Open-Meteo Marine API, MeteoFrance sea-surface temperature dataset. Nearest sea grid cell (-32.04, 115.54). Each month is the mean of yearly monthly means; the range is the lowest and highest of those yearly monthly means. Open-Meteo methodology.
Water temperature by month
Each month uses the 2023–2025 baseline. The range is the lowest and highest yearly monthly mean, not an hourly extreme.
Rottnest Island in January
Typical January water temperature near Rottnest Island is 22.5°C (72.5°F), with yearly monthly means from 21.8–22.9°C.
Rottnest Island in February
Typical February water temperature near Rottnest Island is 22.4°C (72.3°F), with yearly monthly means from 22.3–22.5°C.
Rottnest Island in March
Typical March water temperature near Rottnest Island is 22.6°C (72.7°F), with yearly monthly means from 21.9–23.3°C.
Rottnest Island in April
Typical April water temperature near Rottnest Island is 22.4°C (72.3°F), with yearly monthly means from 21.5–23.4°C.
Rottnest Island in May
Typical May water temperature near Rottnest Island is 22.1°C (71.8°F), with yearly monthly means from 21.1–22.7°C.
Rottnest Island in June
Typical June water temperature near Rottnest Island is 20.7°C (69.3°F), with yearly monthly means from 19.7–21.3°C.
Rottnest Island in July
Typical July water temperature near Rottnest Island is 19.3°C (66.7°F), with yearly monthly means from 18.4–19.9°C.
Rottnest Island in August
Typical August water temperature near Rottnest Island is 18.7°C (65.7°F), with yearly monthly means from 18.2–19.1°C.
Rottnest Island in September
Typical September water temperature near Rottnest Island is 18.5°C (65.3°F), with yearly monthly means from 18.0–18.8°C.
Rottnest Island in October
Typical October water temperature near Rottnest Island is 19.1°C (66.4°F), with yearly monthly means from 18.9–19.2°C.
Rottnest Island in November
Typical November water temperature near Rottnest Island is 19.9°C (67.8°F), with yearly monthly means from 19.6–20.1°C.
Rottnest Island in December
Typical December water temperature near Rottnest Island is 21.6°C (70.9°F), with yearly monthly means from 21.3–22.0°C.
Forecast archive (growing)
These values come from hourly forecasts SnorkelForecast has stored. They cover only months with records and do not replace the historical baseline.
| Month | Min | Average | Max |
|---|---|---|---|
| June | 19.3°C / 66.7°F | 20.2°C / 68.4°F | 21.6°C / 70.9°F |
| July | 18.6°C / 65.5°F | 19.3°C / 66.8°F | 20.3°C / 68.5°F |
| August | 18.3°C / 64.9°F | 18.7°C / 65.7°F | 19.5°C / 67.1°F |
| September | 18.0°C / 64.4°F | 18.6°C / 65.4°F | 19.3°C / 66.7°F |
Partial coverage: 4 calendar months with records. Profile calculated from 2734 hourly forecast records across 4 monthly periods. This is a growing archive, not a long-term climate normal.
About the water at Rottnest Island
Island off Perth with sheltered bays, seagrass meadows and shipwreck snorkel trails.
- Area
- Western Australia
Rottnest Island Water Temperature: Common Questions
What is the water temperature in Rottnest Island today?
The current sea surface temperature near Rottnest Island is 18.9°C (66.0°F). Over the last 30 days, the average has been 18.5°C.
When is the water warmest in Rottnest Island?
The water is typically warmest in March, at around 22.6°C (72.7°F) in the 2023–2025 historical baseline.
When is the water coldest in Rottnest Island?
The water is typically coldest in September, at around 18.5°C (65.3°F) in the same historical baseline. A wetsuit is usually recommended during this period.
Can you swim in Rottnest Island today?
The water is 18.9°C. It may feel cool, but a wetsuit or short swims can help.
Full Snorkeling Forecast
See how today's sea temperature, wave height, wind, and tides combine into a detailed snorkeling score for Rottnest Island.
View Snorkel Forecast →