Tropical cyclone Seroja gathers strength as it heads towards WA

Western Australians have been warned of a strengthening tropical cyclone heading towards them from Indonesian waters.

Tropical Cyclone Seroja formed near the Timor Island north of Western Australia in the early hours of Monday morning, Weatherzone meteorologist Joel Pippard said.

Earlier today, Seroja was producing winds of up to 100km/h and is expected to gain strength as it tracks down parallel to the WA coast later this week.

The system had a high chance of becoming at least a category 3 severe tropical cyclone by Wednesday and possibly becoming a category 4 later on, Mr Pippard said.

"For most of the north coast, rough seas and somewhat gusty winds will be the worst of the weather experienced during the next few days, depending exactly how far the system is from the coast," he said.

"However, from about Thursday or Friday, Seroja will start to interact with another tropical low or cyclone coming from near Christmas Island, with its track becoming very uncertain as a result."

While it was still not clear where or if the cyclone would make landfall, there was a risk it could impact the Pilbara and Gascoyne coasts, Mr Pippard said.

The cyclone could lead to wild winds of more than 120km/h and heavy rainfall of more than 200mm, he said.