The river system south of the town, which is still recovering from severe flooding two weeks ago, was expected to see a 200 ml rise in the water level, he added.
It will lower to a category two cyclone before dying into a low-pressure system on Saturday morning,
The coastal stretch to the east of Exmouth was already suffering a "very dangerous storm tide", Mr Watkins said.
"At the strength we're talking about with Olwyn, anything that is not strapped down could become a missile - trees and power lines could be brought down," Mr Bergin told the WA Today news outlet.
12 March 2016Last updated at 21:53
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Cyclone Olywn brings winds to Western Australian coast
Cyclone Olwyn is seen just before hitting the WA coastline near Exmouth
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The wind speeds near the eye of the storm were potentially "very destructive", Austen Watkins, a tropical cyclone forecaster from the Bureau of Meteorology, told the BBC.