Tropical cyclone gathering force off WA coast

A tropical cyclone forming off the coast of Western Australia is forecast to gather strength from today.

Tropical Cyclone Herman began as a low pressure system off the Cocos-Keeling Islands, about 1800km from the northwestern WA town of Exmouth.

The Bureau of Meteorology said the weather system is entering a region of greater wind speed that should enable it to gain strength.

READ MORE: Sydney renter left stunned by real estate ad

"Tropical Cyclone Herman is expected to move to the southeast and intensify over the next 12 to 24 hours," the bureau said early today.

"TC Herman is then forecast to weaken during Friday and Saturday and turn to the west, staying well away from the Australian mainland and any island territories in the Indian Ocean."

This outlook was backed by the US military's Joint Typhoon Warning Centre, which gives a high potential for tropical cyclone development over coming hours.

The bureau said Herman was not expected to impact mainland WA and would lose strength by early next week.

It has issued a severe thunderstorm warning for north-western WA today, with heavy rainfall forecast for the Pilbara, Gascoyne, North Interior and South Interior districts.

READ MORE: Army of ticks 'torture' Sydney grandfather

Tropical cyclones are intense low-pressure systems that form over warm ocean waters at low latitudes.

They form when the sea-surface temperature is above 26.5C, drawing their energy from warm tropical waters.

Cyclones produce gales, torrential rain and storm surges of varying intensity, depending on how low the storm's central pressure becomes.

READ MORE: Australians paying $6 billion for unused parking, study finds

- Reported with Weatherzone

Sign up here to receive our daily newsletters and breaking news alerts, sent straight to your inbox.