By Colin Packham
SYDNEY (Reuters) - A tropical cyclone off Western Australia's northwest coast that has already forced port authorities to close two ports will intensify before making landfall, the national weather bureau said on Thursday.
Tropical Cyclone Olwyn is expected to strengthen to a category three storm hitting land to the west of Australia's largest iron ore export terminal, Port Hedland, the Australian Bureau of Meteorology (BOM) said.
There has so far been no significant disruption at Port Hedland, but the Pilbara Ports Authority said on Thursday that two smaller ports have been closed.
Dampier and Ashburton were cleared of all vessels on Wednesday, and both have since been closed.
Dampier is one of two ports used by Rio Tinto to ship iron ore. Ashburton is used by Chevron for its liquefied natural gas (LNG) exports.
More than 140 million tonnes of iron ore was exported from Dampier during the 2013/14 financial year, according to statistics from the Pilbara Ports Authority.
Winds in excess of 165 kilometers per hour could develop, the BOM said, along with heavy rains that may cause flooding.
While Cyclone Olwyn is expected to lash Western Australia, Australia's east coast may be spared, the BOM said.
Tropical Cyclone Nathan was earlier expected to hit Queensland's north coast on Thursday, but current models now suggest the cyclone will reverse course and head back out to sea, the BOM said.
The island nation of Vanuatu to the east of Australia across the Coral Sea, however, is still likely to be hit by Tropical Cyclone Pam. The cyclone has been upgraded to a category four storm, the second highest rating, and is expected to bring destructive winds and heavy rains.
(Editing by Tom Hogue)