Climate indicators shore up wet weather outlook

The Bureau of Meteorology says all climate model outlooks it surveys suggest an Indian Ocean driver associated with increased winter and spring rainfall for much of Australia is likely to form in the coming months.

The Indian Ocean Dipole (IOD) index has been below zero over the past four weeks, with two of those weeks exceeding the negative threshold value. Outlook accuracy for the IOD significantly improves from June.

In the Pacific, the La Nina associated with this year’s wet conditions and flooding is slowly weakening in the tropics and compared to two weeks ago sea surface temperatures have warmed.

Most climate models surveyed by the bureau indicate a return to neutral Pacific conditions during the southern hemisphere winter, while two of the seven models maintain La Nina conditions through the southern winter.

“Warmer than average sea surface temperatures around much of Australia are likely to be contributing to wetter outlooks over the coming months, and the forecast sea surface temperature pattern in the tropical Pacific still favours average to above-average winter rainfall for eastern Australia,” the bureau says.

Australia’s rainfall in May was 40% above average for the country as a whole, driven by conditions in Queensland and NSW.

Daily rainfall records were observed across much of the eastern half of Queensland, northern Queensland, and parts of NSW between May 10 to 14. Multi-day totals to May 15 were two to eight times the average monthly total for large parts of Queensland.

Senior climatologist Andrew Watkins says in a recent outlook that winter is expected to by drier than usual in southwestern Australia and western Tasmania, but parts of central and eastern Australia have an increased chance of being unusually wet.

The rainfall on an already wet landscape means soils are likely to remain wetter than average through the winter months and stream flows are also likely to stay high across eastern Australia during May to July.

“With wet soils and full dams and rivers, the main flood risk this winter moves towards the southeast,” Dr Watkins said.