Sydney is comfortable for travellers to visit any time of year.
The city enjoys over 300 sunny days each year.
(December to February) is the best time to enjoy Sydney's beachside outdoor lifestyle. Temperatures usually reach around 26°C but it can be very hot, with temperatures climbing to over 40°C for a few days each summer. Summer days can be humid, and sometimes have searing dry winds, but they frequently end with a "southerly buster", a cold front sweeping up from the south, bringing a clearly noticeable drop in temperature. Within hours, the storm can pass and the evening continues cooler. Hot windy days can close national parks, walking trails, and ban fires because of the fire risk. Rain is usually in the form of afternoon thunderstorms, that can be intense but usually pass quickly. Occasionally low pressure systems drift down from the tropics, giving periods of more unstable weather.
You won't need to pack much more than T-shirts to visit Sydney in summer, but remember your hat and sunglasses.
March to May) March and April, especially, tend to have clear, warm days with mild nights. There can be good days for the beach in March, but you can't count on it. It is a good time for visiting attractions, going to the zoo, catching ferries around the harbour without the summer crowds. You may need a sweater for the evenings, especially for May.
June to August) is cool, not cold. Average July maximum temperatures are 17°C, and daytime temperatures rarely drop below 14°C, but night-time temperatures can fall to below 10°C. Most rain falls as a result of a few off-shore low pressure systems, which usually result in two or three rainy weeks during winter. The Icebergs will be in the ocean doing their morning laps, but most of Sydney will be well away from the beach. It does not snow in Sydney, and unless you intend spending long periods outside, you can usually get by with just a sweater. Sydney is a year-round city, and only the outdoor water-parks close for the winter. If the beach isn't your scene, and you don't like the heat, winter may be your time to visit.
(September to November). September is Sydney's driest month, and Spring days are great for exploring Sydney's attractions, bushwalking, cycling, and the outdoors. Beaches are generally patrolled from the end of October, and Sydneysiders start flocking to the beaches in November. Sydney's Western Suburbs that lie away from the coast tend to be hotter during the day and a little cooler during the night. They miss the afternoon sea breezes, and the night-time warming effect of the ocean.
Sydney has air conditioning in all public buildings, and on most (but not all) public transport. Carry water during summer.
Remember sun protection year round, as the UV exposure risk can be extreme at any time of year.
Sydney Climate and Weather information is available online at the Australian Bureau of Meteorology: www.bom.gov.au