West coast hit by mini tsunamis

Mini tsunamis generated by intense thunderstorms hit WA's coast in recent days but there was little damage because the tides were not higher, an ocean expert says.

Chari Pattiaratchi, head of coastal oceanography at the University of WA's school of environmental engineering, said a succession of "meteo-tsunamis" had struck from Carnarvon to Busselton since Sunday.

The comments came as another storm swept into Perth yesterday afternoon - the third day in a row the city had been hit by wild weather after high temperatures and stifling humidity.

Neil Bennett, the Weather Bureau's regional manager, said though it was not unusual for Perth to have summer thunderstorms, the extent to which they had persisted was uncommon.

He explained that a holding pattern caused by a low off the eastern seaboard, which was blocking a high pressure system in the Great Australian Bight, was behind the unusual events.

It meant a trough off WA's west coast that was drawing in hot, moist air from the Indian Ocean had also been unable to move and was funnelling storms over Perth. "It's pretty tropical - that would be the characteristic you would describe it as," Mr Bennett said.

The storms have been linked to this week's meteo-tsunamis. Professor Pattiaratchi said monitoring buoys showed one that hit Hillarys about 7pm on Sunday coincided with high tide and brought a 50cm surge in water levels.

He said any effects were minimised because the tides at this time of the year were not particularly high, though he warned the city might not be so lucky the next time they occurred.

Meteo-tsunamis, so called because of their meteorological origin, typically happen when powerful storms and cold fronts travelling in a particular direction push waves in front of them.

They differ from conventional tsunamis, which are caused by open-ocean earthquakes and are more destructive, but have similar characteristics.