The correct answer to the question "What is Willy-Willy?" is option 3: a tropical cyclone of the north-west Australia.

Willy-Willy is a term commonly used in Australia to refer to tropical cyclones that occur in the north-western part of the country. These cyclones are characterized by strong winds and intense rainfall. They are a significant weather phenomenon in the region and can cause widespread damage and disruption.

Tropical cyclones, also known as hurricanes or typhoons depending on the region, are large-scale weather systems characterized by low-pressure centers and strong rotating winds. They form over warm ocean waters and can cause severe weather conditions such as heavy rainfall, storm surges, and high winds. The term "Willy-Willy" specifically refers to cyclones that occur in the north-western part of Australia.

North-west Australia, particularly the Pilbara and Kimberley regions, is prone to the occurrence of tropical cyclones due to its geographical location and warm ocean waters. These cyclones can develop during the tropical cyclone season, which typically runs from November to April. The north-western Australian coastline has experienced significant cyclone activity in the past, with notable examples including Cyclone Tracy in 1974 and Cyclone Yasi in 2011.

The term "Willy-Willy" is derived from the Aboriginal language, where it means "spiraling wind." It is often used colloquially by locals to describe the tropical cyclones that impact the region.

In summary, Willy-Willy refers to tropical cyclones that occur in the north-western part of Australia. These cyclones are characterized by strong winds, intense rainfall, and are a significant weather phenomenon in the region. The term "Willy-Willy" is derived from the Aboriginal language and is widely used colloquially to describe these cyclones.