Neal Brown of Lake Hawea asks :-
Is there a connection between the weather in New Zealand and Australia?
Erick Brenstrum, a meteorologist with the MetService, responded.
The two countries are far enough apart that they can have opposite weather when a large-scale trough stalls over the Tasman Sea. Then New Zealand experiences warm northerlies while Victoria and New South Wales have cold southerlies.
However, hot air from Australia will sometimes cross the Tasman Sea and bring high temperatures to parts of New Zealand.
Many of our warm days are caused by air arriving from the northwest which has been over warm ocean offshore from Queensland rather than the continent. East of Australia a warm ocean current transports water away from the tropics towards higher latitudes. In fact, there are warm currents east of all the continents. Conversely, there are cold currents running up the west side of continents moving cold water from high latitudes towards the tropics.
These currents have a profound influence on the weather. Cold currents cool the air above them making it denser than the air higher up. Consequently, the air resists upward motion thereby suppressing rain and causing deserts over the adjacent land. By contrast, warm currents on the eastern side of continents encourage rain by heating the air, making it unstable and more likely to rise.
Drive north of Perth and you reach desert: drive north of Sydney and you find rainforest. Similarly, California is dry while Florida has swamps and alligators. The coast of northern Chile and Peru has the Atacama Desert, while the east coast of South America has agriculture.
The warm ocean east of Australia also promotes the rapid deepening of depressions over the Tasman Sea, many of which move southeast bringing stormy weather to New Zealand. Easterly winds on the southern side of these lows bring rain to places such as Canterbury, Wairarapa and Hawkes Bay that are sheltered from rain carried by the normal westerly winds.