WA: Widespread rain breaks May records across WA Wheatbelt
Wed 05 May 2021

A trough and low pressure system have brought heavy rain across the Wheatbelt and Great Southern on Tuesday and overnight into Wednesday breaking many May records, some that have stood for over a century.

Northam in the Central Wheatbelt and Colorado, Corrigin, Kojonup and Redlands in the Great Southern all have well over a hundred years of rainfall observations. Kojonup, with a near-perfect set of observations back to 1885 was notable. It smashed its former May one-day record of 54.2 set on 21 May 2014 by recording 81.2mm, the highest total in southern WA. Bickley on the eastern outskirts of Perth had 71.2 in the gauge and Wickepin 70.4.

The unusually heavy rain was caused by the movement of the low. It lay off the WA West Coast on Tuesday, dragging cloud and deep moisture down its eastern side but cut across SW WA overnight from Kalbarri to Esperance. This brought the moisture, instability and rain through the Wheatbelt and Great Southern.

Even heavier rain fell in the Pilbara due to a second trough. Barrow Island registered 103.2mm for the 24 hours to 09:00 Wednesday, more than twice its average monthly rain for May. Roebourne followed up with 86.2mm.

The rain map shows that a large part of the western third of the state recorded over 25mm of rain and AWN's rain list shows totals over 50mm.

 NSW: Lines of showers accumulate big totals on NSW South Coast
Wed 05 May 2021

On the other side of the country, another trough brought heavy rain to parts of the Illawarra and South Coast from about 23:00 Tuesday as lines of showers following the same track moved onshore into the coastal mountains.

The heaviest of these shower lines was in the Bega Valley where all of the BoM's Flood Gauge Network reported more than 100mm. The heaviest 24 hour total to 09:00 Wednesday was 156mm at Black Range, 5km S of Bega, with 75mm falling in 2 hours to 03:00. The Bega AWS reported 115.0mm, breaking its May record of 75.2 in 26 years of operation.

Other heavy shower lines crossed the coast around Ulladulla where a small low developed briefly near midnight. Lake Tabourie just to the south had an 09:00 total of 100mm and heavy rain extended SW along the coastal mountains to between Braidwood and Batemans Bay.

A third area of heavy showers moved up the Shoalhaven River valley bringing rain totals of 50 to 150mm. The heaviest were on the arc of escarpments from N to SW of Nowra with Mongarlowe, 20km NE of Braidwood, highest with 82mm to 09:00 and a further 74 to 17:30.

During the afternoon, a low developed in the trough off the NSW North Coast. It's the residue of a cut-off low that has moved from the Southern Ocean, through western and northern NSW to the SE QLD coast over the past two days. This has begun to move down the coast but, because it is dragging the heavy showers with it, showers are not lingering as they did on the South Coast overnight so totals to 18:00 have been less than 25mm.