SYDNEY (Reuters) - Australia can expect an average cyclone season with up to 11 tropical storms, four of them severe, in the next six months, the Bureau of Meteorology forecast said on Monday.
Australia's cyclone season runs from November 1 to April 30 with storms forming in the tropical waters off the northeast and northwest coasts before making landfall.
Each year, cyclones close shipping lanes and disrupt mining of hundreds of millions of tonnes (1 tonne = 1.102 metric tons) of iron ore, coal and other commodities in Australia.
Last February, Cyclone Rusty, packing winds up to 200 kms (120 miles) per hour, closed the Indian Ocean ports of Cape Lambert and Dampier ports used by Rio Tinto. It also closed nearby Port Hedland, used by BHP Billiton and Fortescue Metals, which handle 500 million tonnes of iron ore annually between them.
Flooding caused by cyclones in eastern Australia in January 2011 disrupted about 40 percent of the world's metallurgical coal exports and 8 percent of the world's thermal coal exports
"Near average tropical cyclone activity is most likely for the Australian region this season," the bureau said, citing a neutral outlook for El Nino and La Nina weather events.
In the absence of El Nino or La Nina, cyclone numbers around Australia are most often close to average, though individual years can be above or below the long term mean, it said.
The last time the number of cyclones exceeded the national average was in 2005/06, when 14 cyclones were recorded, nine categorized as severe.
Only cyclones with winds above 165 kms per hour (100 miles) are classified severe by the bureau.
Australia on average sees its first cyclone make landfall in late December.
(Reporting by James Regan; Editing by Michael Perry)