Higher than average sea surface temperatures, a monsoon trough and "favourable" winds in the atmosphere's upper layer have combined to create what locals fear could be one of the biggest cyclones to hit the Pilbara in years.

The slow-moving nature and size of severe tropical cyclone Rusty made it difficult to pinpoint its landfall crossing time and location, the Weather Bureau's Neil Bennett said.

"It's such a slow-moving system and there's a fairly broad area from Bidyadanga to Mardie that could be affected by 150km/h-plus winds, and if it gets to a category four we could start seeing in excess of 200km/h winds," he said.

He warned there was likely to be a lull as the eye crossed the coast before gusts of up to 200km/h returned. Images from NASA's Terra satellite show Rusty developing an eye spanning 20 nautical miles.

Mr Bennett said Rusty would be most damaging if the eastern side of the storm surge crossed near Port Hedland.

Grahame Reader, manager of weather services at the bureau, said sea temperatures were higher than normal.

"Sea surface temperature always has an impact because that's where cyclones draw their energy from," he said. "But probably the more important determinant is the winds in the upper layer of the atmosphere, which have allowed it to develop to its full potential."

The West Australian

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