Weather in Sydney in December

The month to avoid. Of the twelve, December is the one to avoid. Highs sit at 2.7 °C and the day is short; this is an indoors-with-excursions month, not an outdoors-all-day one.

December ranks 11 of 12 — near the bottom of Sydney's year. July is the month that works, and the swing between the two is 65 points, which is a different holiday rather than a slightly better one.

Rain on 17 days, 4 of them heavy. Enough to need a plan B, not enough to need a plan around it. Layers, and a genuinely waterproof outer — at 2.7 °C the difference between a good day and a miserable one is entirely down to what you are wearing.

What the averages hide

Averages flatten a month, and this one hides a few things: 22 nights drop below freezing, so anything left outside stays frozen; the day barely swings — 4.7 °C between the overnight low and the afternoon high. Across the twenty years measured, the hottest December day reached 12.9 °C and the coldest night fell to -13.4 °C, and the wettest single day dropped 54 mm — roughly 40% of the month's rain in one day.

December is statistically steady but not small: the year-to-year variation is modest in relative terms, yet the wettest December on record still delivered 312 mm against 96 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 136 mm average is a reasonable planning figure, not a promise.

Wind sits around 24.6 km/h — a steady breeze rather than a nuisance, and welcome on the warmer days, and humidity runs at 85%, which at 2.7 °C means damp rather than muggy — the kind of cold that gets into a coat and stays there.

How December sits in the year

The month is on the way down: 5.1 °C cooler than November, with January dropping another 3.3 °C. The first week and the last are not the same trip.

Daylight in December

December sits at the dark end of Sydney's year — 8.7 hours of daylight against 15.7 at midsummer, holding steady all month. Sightseeing days are genuinely shorter, and an itinerary built for summer will not fit.

Sea temperature

The sea sits at about 4.7 °C in December — too cold to swim without a wetsuit. The sea peaks at 18.4 °C in August and bottoms out at -0.2 °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.

December in Sydney versus nearby

If Sydney is one option among several, the nearby comparison is worth making. Halifax is close enough to be a coin toss — within a degree on temperature, 3 days less rain. Moncton is close enough to be a coin toss — 2.7 °C cooler, 4 days less rain.

So: December is a compromise. July is 62 points better and is what Sydney 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 Sydney

See all twelve months in Sydney, or where else to go in December.