This Saturday, June 21, marks Australia’s winter solstice, the shortest day and longest night of the year for the Southern Hemisphere. But if you’re bracing for bone-chilling temperatures as soon as the sun sets, you may be surprised: according to meteorologists, Australia’s coldest weather usually hits weeks after the solstice, thanks to a phenomenon called seasonal lag.

Across the country, daylight hours on Saturday will vary dramatically by latitude. Down south, Hobart will shiver under just 9 hours and 1 minute of daylight, while tropical Darwin still enjoys 11 hours and 24 minutes. Here’s how the capitals line up, south to north:

• Melbourne: 9h 32m
• Canberra: 9h 46m
• Adelaide: 9h 48m
• Sydney: 9h 54m
• Perth: 10h 3m
• Brisbane: 10h 24m

The winter solstice happens because of Earth’s 23.5-degree tilt. As we orbit the sun, this tilt shifts how directly sunlight strikes our part of the planet — giving us short days in winter and long days in summer.

This year, the solstice occurs at 12:42pm for eastern states, just after noon for the NT and SA, and 10:42am for WA — meaning Friday night is technically the longest for the west coast.

So why isn’t it coldest on the shortest day?

From a simple energy perspective, the solstice brings the least direct sunlight, so you’d expect it to be the chilliest time of year. But for nearly all of Australia, the true depths of winter lag behind.

Why? Oceans hold the answer. Land heats and cools quickly, but water does not. The vast seas surrounding Australia absorb warmth through summer and autumn, then slowly release that stored heat back into the air.

So, even as the sun’s energy drops to its minimum in late June, the oceans act like giant heaters — delaying the coldest nights until mid-to-late July. This heat lag is why coastal cities like Sydney, Melbourne, Perth, and Adelaide usually see their coldest days in the second or third week of July — weeks after daylight hours start increasing again.

Just how much delay are we talking about?

According to the Bureau of Meteorology:

• Southwest Tasmania and coastal WA towns like Albany have the longest lag — about five weeks past the solstice.
• Major cities including Sydney, Melbourne, Brisbane, Perth and Adelaide average their coldest days about three weeks after June 21.
• Inland areas, far from ocean influence, feel the chill sooner — sometimes just a few days after the solstice.
• For minimum overnight temperatures, more than 90% of Australia hits its coldest nights between July 11 and 21.

Northern Australia’s weather is trickier: cloud cover and tropical dynamics mean some regions actually record their coolest daytime highs slightly before the solstice.

Seasonal lag happens elsewhere too

Australia isn’t alone. Seasonal lag is a global quirk. In San Francisco, for example, the warmest month is September — three months after the longest day in June. The same lag explains why southern Australia’s hottest days arrive in January, even though the summer solstice is in late December.

Of course, weather is famously unpredictable. Cold snaps can hit anytime from April to November. But if you’re counting on July’s frosty mornings and icy nights, the odds are firmly in your favour.

So bundle up — but maybe not quite yet. This solstice is just the start.