Late Summer Heatwave Grips Much of Eastern Australia (Credit: The Sydney Morning Herald and Australian Bureau of Meteorology)

DISCUSSION: As Southern Hemisphere Fall settles in, Australia also winds down on the summer heat experienced since earlier this year. But last weekend, a considerable late-summer heat wave held a firm grip on the eastern Australian coast. Sydney recorded a trio of consecutive days with high temperatures above 30°C (86°F), a streak that has not been observed in the New South Wales capital since 1902 and only once more in 1889. Saturday afternoon also saw high temperatures exceed 30°C in all of the eastern capitals (e.g. Adelaide, Melbourne, Sydney, Brisbane, Canberra, and Hobart) for the first time since 1965. Inland locations of New South Wales and Queensland saw the mercury soar to near 40°C (104°F) which set new daily records in stations such as Albion Park.
 
The heat generated over the last couple of days was largely due in part to a strong low-pressure system and associated cold front moving east over the Great Australian Bight. This low-pressure system promoted southeasterly advection of hot air from the Australian Outback. In addition, a high-pressure system was located over southern Queensland. Sunny skies prevailed as plenty of subsidence was induced by the more stable airmass. The combination of these two features in close proximity creates a tight pressure gradient which led to average wind speeds in excess of 20 mph over much of the east coast for much of the afternoon hours on Sunday. The high temperatures and brisk winds combined to spark several bushfires along the Far South Coast, including the town of Tathra where damage and destruction to over 100 houses and caravans were reported through Monday morning.
 
On a global scale, the weather patterns resemble typical conditions during a La-Niña event. La-Niña is the term that describes a cooling of the Eastern and Central Pacific sea surface temperatures, shallowing of the ocean thermocline (e.g. the slope of lines of constant temperature) towards the surface, and elevated trade winds in the near-equatorial latitudes. Direct effects on Australia from La-Niña include a slight cool departure in temperatures and wetter than normal conditions, which makes this event highly anomalous.
 
Fortunately, a reprieve from this heat wave is in store for the rest of this week for much of the South Coast. A high-pressure system over the Tasman sea will induce southeasterly flow onto the mainland. At the same time, a shortwave trough is expected to move east towards New South Wales which is expected to destabilize the atmosphere enough for thunderstorms to develop. The Sydney area could expect to see rainfall accumulations above 50 mm through Saturday. Those along the Hunter Coast (e.g. including cities like Newcastle and Port Stephens) may expect upwards of 100 mm, which is why the Bureau of Meteorology has issued a severe storm watch and a flood watch. This onshore flow and greater cloud coverage should also keep afternoon temperatures in check. However, much of inland Queensland won’t see much in the way of rain over the next few days as continued subsidence prevails, keeping much of the state in a substantial drought.
 
Image credits: David Porter; Australian Bureau of Meteorology
 
To learn more about other high-impact weather events occurring across Australia and the South Pacific Ocean, be sure to click here!
 
© 2018 Meteorologist Brian Matilla