Perth Marine Forecast
Updated Fri Sep 11, 2026
Building swell and steep chop make this a weekend to stay ashore
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Marine Forecast for Perth Sep 11–13, 2026
📋 Building swell and steep chop make this a weekend to stay ashore
Calm NE winds and smooth 14-second WSW swell dominate the morning, but a NNE-to-NW wind-wave builds from late morning and crosses the swell, creating a confused, choppy sea into the evening. Best window is before 10:00 AM; use caution after midday.
Dangerous conditions with 19-22 knot winds gusting to 30 knots overnight and steep 6-8 ft seas at short periods - the roughest day of the forecast. Even the calmer afternoon still holds 7.4-7.7 ft swell, keeping seas unsafe all day. Avoid boating entirely.
Winds ease to a pleasant 8-12 knots, but a lingering 6.3-6.6 ft WSW swell at 11-12 second periods keeps seas too rough for safe boating all day. Despite the calm breeze, this remains a no-go day due to residual swell.
A large WSW groundswell builds through the weekend, combining with a crossing NNE wind-wave on Friday and outright rough seas Saturday and Sunday to produce unsafe conditions for recreational boating. Only Friday morning offers a genuinely workable window before seas deteriorate; Saturday and Sunday are dominated by steep, breaking swell well above comfortable limits.
Recent days at Perth
Today’s Water at Perth
Sea surface temperature and chlorophyll around Perth, imaged fresh every morning. Water at the star is 63.9°F today, and chlorophyll of 0.53 mg/m³ reads as green shelf water at the spot.
Imagery: Sep 10, 2026 · rebuilt every morning
These charts show you the breaks. DeepCast reads them. A zone-by-zone AI fishing report for these exact waters — temperature edges, color changes, and structure, analyzed together — for $4.99.
Get the AI fishing reportSST and chlorophyll from the SeaLegs AI DeepCast satellite pipeline. Charts are a planning aid — always check the official marine forecast before making the run.
About Perth
Boating out of Perth runs on a clock. Through the warmer months the morning is usually the calm part of the day and the afternoon belongs to the Fremantle Doctor — the southwesterly sea breeze that arrives with near-daily reliability and turns the water over.
The outlook below updates every morning from the latest marine model data, and each day gets an honest GO, CAUTION, or NO-GO call — the same AI rating used in the SeaLegs AI app.
Reading the Fremantle Doctor
The Doctor is a southwesterly sea breeze that commonly blows 15 to 20 knots and typically sets in somewhere between late morning and mid-afternoon — often around the early afternoon — and it is at its strongest in December and January, when the temperature difference between land and sea is greatest. It is welcome relief ashore. On the water it means a short, building chop through the afternoon.
The practical consequence is that Perth days are usually decided by timing rather than the daily average. A forecast that reads moderate across the day can still offer a genuinely calm morning window and a difficult afternoon one. If you're heading offshore, plan to be well on your way back before the breeze fills in, and read the hour-by-hour trend below rather than the day's headline number.
Perth forecast FAQ
How is the sea at Perth today?
As of Sep 11, 2026, the SeaLegs AI verdict for Perth is CAUTION. Friday starts well with light 11-16 knot NE to NNE winds and a long-period 4.3-4.7 ft WSW swell at 14-second periods, giving smooth, well-organized conditions through the morning into early afternoon. From late morning onward a NNE-to-NW wind-wave develops and begins crossing the underlying WSW swell, producing a confused cross-sea where the two wave trains arrive from different directions and create an awkward, uncomfortable motion with no single comfortable heading - this steep wind-wave chop persists for around 9 hours and the crossing pattern for about 8 hours. Winds stay mostly moderate (occasionally touching 18 knots NW with gusts near 23 knots in the late afternoon), but the building cross-sea is the main reason for caution today, especially from midday onward.
What is the Fremantle Doctor?
It's the southwesterly sea breeze that blows into Perth on most warm-season afternoons, commonly at 15 to 20 knots. It usually arrives somewhere between late morning and mid-afternoon and is strongest in December and January. For boaties it's the main reason mornings are typically the calmer part of a Perth summer day.
How accurate is this Perth marine forecast?
The outlook is generated from the latest marine model data and rated GO, CAUTION, or NO-GO by the same AI engine used in the SeaLegs AI app. It's a planning aid, not a substitute for the Bureau of Meteorology's coastal waters forecast and marine warnings — always check those before heading out.
How often is this forecast updated?
The page is rebuilt every morning from the latest model run, and the SpotCast card refreshes live in your browser. The date stamp above the outlook shows when it was last generated.
What do GO, CAUTION, and NO-GO mean?
GO means conditions are favourable for most recreational boats. CAUTION means marginal — manageable for experienced crews in capable vessels, but check the wind and sea timing closely. NO-GO means conditions are hazardous for small craft and the trip is best postponed.
What is the water temperature at Perth today?
As of Sep 10, 2026, the satellite-derived sea surface temperature at Perth is about 63.9°F, with chlorophyll around 0.53 mg/m³ (green shelf water). The SST and chlorophyll charts on this page are rebuilt every morning from the SeaLegs AI DeepCast satellite pipeline.
More offshore forecasts
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