September in Melbourne, Australia, brings average daily highs of 17°C and overnight lows of 8°C in the 2016–2025 historical record. Bring layers that work for a longer spell outside as well as a short walk. A warm extra layer gives you options when the day's weather feels cooler than the monthly average suggests.
In the record, at least 1 mm of rain or snow falls on 12 of 30 days on average, a daily chance of 39%. Give wet-weather alternatives a proper place in the itinerary. Arrange outdoor plans so you can move them between days, and pack a rain layer rather than relying on a completely dry run of weather.
The calculated day length, sunrise to sunset, averages about 12 hours. Sunshine averages 9 hours a day. Use the daylight window to plan the length of excursions, and check local sunrise and sunset times for the dates of your stay. Sunshine is a separate measure, and those hours need not arrive in one uninterrupted stretch.
If the coast is part of your plan, check water conditions separately. Air temperature and sunshine do not establish swimming conditions, surf quality or diving visibility. For a culture-focused visit, group the places you want to see into manageable areas, with time between stops. Check each venue's opening dates before fixing the order.
October has an average daily high of 20°C, 3°C higher than September. Its historical rain-day chance is 37%, compared with 39% this month. If your dates are flexible, compare those trade-offs with the kind of days you want. Neither set of averages predicts the conditions of one particular holiday.