Neutral El Niño leaves 50-50 chance of early or late North West monsoon rainfall onset

A neutral El Niño weather pattern is leaving models uncertain about when the rains will arrive in the North West as the rest of northern Australia prepares for early monsoonal rainfall.

In its final northern rainfall onset update of the year released this week, the Bureau of Meteorology predicted most of the North West had roughly equal chances of an early or late rainfall onset.

The one exception was the East Kimberley, which had a 60 per cent likelihood of monsoonal rains arriving early this season.

This was in line with most of northern Australia, which has up to an 80 per cent chance of seeing early significant rains after September 1.

BoM said the El Niño–Southern Oscillation was currently neutral and that most climate models indicated the central tropical Pacific was likely to cool in the coming months.

“In the Indian Ocean, a negative Indian Ocean Dipole is forecast for spring and likely to return to neutral IOD in December, which is typical of the IOD seasonal cycle,” BoM said.

Modelling for all years shows the onset — when rainfall total reaches 50mm — usually arrives in November in the East Kimberley, December in Broome and surrounds, and January-February in the Pilbara.

Broome has recorded 19.8mm of rain so far over the dry season, with the last significant rainfall occurring in mid-June.

Port Hedland has recorded 34.8mm this dry season and Newman 10mm.

Further south it has been an unseasonally wet dry season — Karratha recorded 115.2mm, Paraburdoo 48mm, Onslow 111.6mm and Exmouth 260.9mm.

Carnarvon has recorded 155mm since the start of May.

No rain has been registered in Kununurra since March.