Cyclone Olwyn heads for WA's Pilbara coast

Residents in WA's north are being warned to prepare their homes for Cyclone Olwyn, which has formed north of the state.

A blue alert has been issued for people in or near communities between Whim Creek and Ningaloo in the Pilbara.

That includes people in Point Samson, Wickham, Roebourne, Karratha, Dampier, Onslow, Pannawonica, Exmouth and surrounding areas.

The Bureau of Meteorology says the tropical low is about 500km north of Karratha and 660km northeast of Exmouth, and is moving south at 9km/h.

Olwyn could reach cyclone intensity by Thursday morning and is likely to reach the west Pilbara coastline on Friday morning.

Gales up to 100km/h are forecast between Karratha and Exmouth late on Thursday.

If the system takes a more southerly track on Thursday, then gales might develop as far east as Port Hedland.

Heavy rain was likely to develop over the western Pilbara and northern Gascoyne on Friday and Saturday, and could lead to flooding, the bureau said.

The Department of Fire and Emergency Services has warned residents to prepare their homes and family for a possible cyclone, including organising an emergency kit with a portable battery-operated radio, torch, spare batteries and first-aid kit.

The Pilbara Ports Authority expected to have all port anchorages cleared by 6pm on Wednesday.