Weather in Perth in September

A good month. September works. It is not the peak, but nothing about it fights you. Highs average 18 °C, lows 13.3 °C, and rain falls on 11 days — nothing in the month is working against you.

September ranks 9 of 12 in Perth: past the worst of the year but short of January, which is the month to book if the dates are open.

Rain on 11 days, 2 of them heavy. Enough to need a plan B, not enough to need a plan around it. Nothing specialised needed — this is the month you pack for the trip rather than for the weather.

What the averages hide

Averages flatten a month, and this one hides a few things: it never really gets hot: not one day in an average September reaches 30 °C; the day barely swings — 4.7 °C between the overnight low and the afternoon high. Across the twenty years measured, the hottest September day reached 25.5 °C and the coldest night fell to 8.2 °C, and the wettest single day dropped 28 mm — roughly 40% of the month's rain in one day.

September is moderately variable: 15 mm in the driest year against 147 mm in the wettest, around an average of 70 mm. Roughly two Septembers in three land near that average, and the third does something else entirely.

Wind sits around 18.4 km/h — a steady breeze rather than a nuisance, and welcome on the warmer days, and humidity is unremarkable at 73%.

How September sits in the year

Temperatures hold steady either side: 17.6 °C in August, 18 here, 19.9 in October. Nothing about the timing within the month matters much.

Daylight in September

11.9 hours of daylight, gaining 1 hours across the month. That is between Perth's extremes of 14.2 and 10.1 hours, so days are long enough not to constrain the plan.

Sea temperature

The sea sits at about 19 °C in September — swimmable, but it takes a moment to commit. The sea peaks at 22.9 °C in March and bottoms out at 19 °C — water lags the air by a month or two, which is why the best swimming often comes after the best weather.

How busy it gets

Quiet. Few other visitors, cheaper rooms, and a real chance some seasonal operators are shut.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

September in Perth versus nearby

If Perth is one option among several, the nearby comparison is worth making. Bunbury is close enough to be a coin toss — within a degree on temperature, 3 days more rain. Geraldton is a better bet in September — within a degree on temperature, 5 days less rain.

So: September is a compromise. January is 24 points better and is what Perth is actually like at its best — worth moving the trip for if that is possible, and worth adjusting expectations for if it is not.

Every month in Perth

See all twelve months in Perth, or where else to go in September.