Australia Weather by Month: 416 mm of Rain in Cairns in January, 23 mm in Perth

Cairns averages 416 mm of rain in January; Perth, 23 mm — an 18-fold difference. Australian weather needs flipping twice. First, it's the southern hemisphere, so the seasons run opposite to Korea's: Korea's July–August holidays land in Sydney's and Melbourne's midwinter. Second, north and south have opposite wet seasons: the tropical north (Cairns) is wet in summer (December–March), while the Mediterranean-climate south-west (Perth) is wet in winter (June–August).

Visit Sydney in Korea's July or August and you get 17–18°C days and 8°C nights; T-shirts alone won't cut it after dark. Melbourne is cooler still: 13.3°C by day, 6.5°C at night in July. Many Australian homes and hotels are less heated and insulated than Korean ones, so visitors often end up wearing knitwear indoors in winter.

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Melbourne is famous for "four seasons in one day". Its January average high is the same 26.6°C as Sydney's, but it gets 4.6 days above 33°C — more than twice Sydney's 1.9.

Melbourne's summer problem is volatility, not the average. A north wind off the inland desert can push it into the high 30s in a day, and a southerly change can drop it below 20°C within hours. Locals carry a light layer even in midsummer.

Cairns, gateway to the Great Barrier Reef, is best from June to October: August brings 37 mm of rain, 9% of January's 416 mm, and 24–26°C days. That lines up exactly with Korea's summer holidays. In the December–March wet season, passing cyclones cancel reef trips and cloud the water.

The Gold Coast runs a season warmer than Sydney, with 20°C days even in July, so winter (Australian) surfing and theme-park trips work. From June to November humpback whales migrate along the coast and whale-watching tours run. February–March is the wettest stretch (225 mm in March).

Perth has hot, dry summers: 9 mm of rain in December and 8.2 days above 33°C in February, though low humidity keeps the shade cool. Its rain falls in winter (June–August), so Perth is best in the Australian spring and autumn (March–April, October–November).

Clothing advice is for Sydney. Go one step warmer in Melbourne all year; Cairns is T-shirt weather year-round.

• Period and source: daily values from Open-Meteo's historical weather data (ERA5 reanalysis), 2016–2025, averaged by month at each city-centre coordinate.
• Versus official normals: reanalysis temperatures usually land within 1–2°C of station normals, but downpours get smoothed out, so monthly rain totals come out lower and rainy-day counts slightly higher.
• Rainy day: at least 1 mm of precipitation. Reanalysis picks up even light showers, so counts run high — especially in the tropics, where monthly millimetres are the better guide. Most tropical rain is an hour or two of downpour, not a washed-out day.
• Best months: a first pass from temperature, rainy days and humidity, then adjusted for seasonal factors such as southern school holidays, the tropical wet season and cyclones, and stinger season. It is a judgement call.