A remarkable mid-year wet spell has caused widespread and prolonged flooding across inland NSW, which is far from over.
The state just experienced its wettest September on record, picking up three times its long-term average rainfall for the month. Most of this rain fell west of the ranges, with close to average falls observed along the eastern seaboard.
The sodden month helped produce riverine flooding through a number of inland river catchments from the North West Slopes and Plains down to the Riverina. One of the standout events was major flooding in the Lachaln River, which forced Forbes residents to evacuate before water entered their houses.
September will go down in the state’s history as a significantly wet month, although it can’t be solely blamed for the flooding situation that continues to grip inland catchments today.
NSW has now experienced above average rainfall for five consecutive months. This included the state’s wettest May in 16 years, third wettest June on record and the third wettest winter on record. As a result, catchments west of the Divide were already saturated before the wettest September on record had even started.
The string of wet months was caused primarily by above average sea surface temperatures surrounding northern and eastern Australia and the strongest negative Indian Ocean Dipole (IOD) in recorded history. Warm water at the surface of the ocean causes more moisture to enter the atmosphere through evaporation, providing extra fuel for rain-bearing systems crossing the country.
The rest of this week will be generally dry before rain returns next week with the passage of a front.
As we move further into the second month of spring, we are still being influenced by the negative IOD and warmer-than-usual waters to Australia’s north and east. As a result, rainfall is expected to remain above average across inland NSW during October.
Climate models suggest that more typical conditions are favoured in November as the IOD gradually weakens into late spring.
