The Australian Broadcasting Corp. said Rusty's winds were roaring up to 125 miles per hour near its center. The powerful storm, about 125 miles wide, was expected to still be at Category 4 when it hits land somewhere between Port Hedland and Pardoo sometime during the afternoon, the ABC said.
Forecasters predict Rusty will saturate parts of Australia with up to 24 inches of rain in a 24-hour period, the ABC said.
People living in the red alert area have been warned to take shelter or a prolonged period because the storm is moving forward so slowly.
"Unfortunately it's not typical of the cyclones we get up here, that take about 12 hours to cross, and we say goodbye to that one, and focus on the next one," Les Hayter of the Department of Fire and Emergency Services said.
"I really feel sorry for the people in red alert mode at the moment. This is going to be for a very long period of time."
Mike Bergin of the Bureau of Meteorology said Port Hedland will experience the equivalent of Perth's entire winter rainfall in just three days.
"It's going to be a long, protracted and quite dangerous experience," he said.