Why Sydney's summer heat comes with a harbour breeze and a sudden southerly change
Sydney's summer is built around two great cooling forces: the Pacific Ocean and the southerly buster. The city sits on a deep, drowned river valley, so the harbour and the coastline are never far from the suburbs. On a classic summer morning, a north-easterly sea breeze carries cool, moist air off the Tasman and tempers the inland heat by early afternoon. That is why the eastern beaches and harbour foreshores often feel ten degrees milder than the western suburbs. But the same hot, humid airmass that builds over the interior can also trigger a southerly buster, a sharp cool change that marches up the coast from the south, often late in the day. Temperatures can drop fifteen degrees in an hour, the wind swings to the south-east, and the city collectively opens its windows. It is a dramatic relief, and it is also why Sydney's summer weather is less predictable than it looks.