Frequently Asked Questions (FAQ)

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Characteristics and Formation

5. What is the eye and eye wall?

The circular eye or centre of a tropical cyclone is an area characterised by light winds, fine weather and often clear skies. The eye is the region of lowest surface pressure

The size of the eye varies from one cyclone to the next ranging from 10 km to over 100 km. The eye diameter of severe cyclones off the northwest coast tends to be about 20 to 40 km, and are typically smaller than those in some other parts of the world such as the north Pacific. The eye size of Tracy (Darwin, 1974) was just 12 km across. Rosita (Broome, 2000) only had an eye diameter of 20 km.

The eye is surrounded by a dense ring of cloud known as the eye wall. This marks the most dangerous part of the cyclone having the strongest winds and heaviest rainfall. Radar and satellite imagery often show that the eye wall clouds are the inner-most coil of a series of spiral rain-band clouds that extend hundreds of kilometres from the centre and typically produce very strong wind squalls. See a schematic of the eye and eye-wall structure. The eye-wall is not always symmetrical, in fact at any one time it is common for the strongest convection and surface winds to be in one part of the eye wall as shown during Monty (2004).

Broome radar image as Rosita crossed the coast south of the town. The eye wall is clearly visible surrounding the eye.

For more technical description of the eye and eye wall go to the US Atlantic Oceanographic and Meteorological Laboratory's Hurricane FAQ page.