Most people are familiar with the various significant tropical cyclones that have impacted the United States such as Hurricanes Camille, Hugo, Andrew, and Katrina… but what about other areas of the globe? Tropical cyclones can form in most tropical and subtropical oceanic basins. This Discovery Guide visits the southern hemisphere where we will go over the basins, climatology, and meteorology of tropical cyclones that occur there. We will also look at the history of significant tropical cyclones that have occurred there.
Tropical cyclones (known as hurricanes in the North Atlantic and Eastern Pacific and typhoons in the Western Pacific) are
warm-core low pressure systems that act as significant heat engines of the Earth by transporting energy from the tropical regions to the polar regions. In the northern hemisphere, the familiar structure of significant tropical cyclones is that of a large system that rotates counter-clockwise. These tropical cyclones have a calm area in the center known as the eye which is surrounded by the strongest winds and storms in the system in the eyewall. At landfall, northern hemisphere tropical cyclones will have the worst impact on the right side of the cyclone’s direction of movement (for example, if a hurricane is moving north towards the Gulf Coast of the United States, the worst weather will be east of the eye). Due to the
Coriolis effect, southern hemisphere tropical cyclones instead rotate clockwise and have the worst impact at landfall on the left side of the direction of movement. In addition, while the northern hemisphere usually experiences most tropical cyclones from May/June through November, the southern hemisphere usually experiences them from November through April/May.
One of the southern hemisphere’s defining characteristics that impacts its meteorology is the distinct lack of significant land masses when compared to the northern hemisphere. The friction of land helps generate
vorticity which is an essential element in the formation of tropical cyclones.
Synoptically, the land also allows the
Intertropical Convergence Zone (ITCZ) to move away from the equator. This is why, despite the larger area of water, the southern hemisphere climatologically only has on average 31% (Hurricane Research Center, "Frequently Asked Questions") of the amount of tropical cyclones per year globally. This lack of land is also related to why we never see tropical cyclones in the southeastern Pacific basin, as well as why we rarely see any in the southern Atlantic basin.
The main active basins for tropical cyclones in the southern hemisphere are the southwest Indian Ocean, Australian Region, and southwest Pacific Ocean. These are further divided into basins which are warned by various Regional Specialised Meteorological Centres (RSMC) as designated by the World Meteorological Organisation (WMO). These are the southwest Indian Ocean (warned by RSMC Météo-France La Réunion), the southeast Indian north of 10°S latitude (warned by RSMC Meteorology and Geophysical Agency of Indonesia-Jakarta), the southeast Indian Ocean south of 10°S latitude (warned by RSMC Australian Bureau of Meteorology-Perth, WA), the Timor and Arafura Seas and western Gulf of Carpenteria (warned by RSMC BOM-Darwin, NT), the Coral Sea and eastern Gulf of Carpenteria (warned by RSMC BOM-Brisbane, QLD), the Solomon Sea and Gulf of Papua (warned by RSMC National Weather Service- Port Moresby, Papua New Guinea), the Tasman Sea and far southwestern Pacific (warned by RSMC Meteorological Service of New Zealand- Wellington), and the remainder of the southwestern Pacific and Polynesia (warned by RSMC Fiji Meteorological Service- Nadi).
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