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The Role of West African Coastal Upwelling in the Genesis of Tropical Cyclones: a New Mechanism

Michael Diaz & Fredrick Semazzi
Newsletter of the Climate Variability and Predictability Programme, December 2008

In the present study, we investigate a new mechanism related to tropical cyclogenesis associated with upwelling along the northwestern coast of Africa. As one of the most prominent upwelling regions in the world’s oceans, these coastal waters are significantly colder than one would expect at such low latitudes. Driven by persistent northeasterly Trade Winds, which blow parallel to the coast, this upwelling produces the southward flowing Canary Current, which entrains the chilled coastal waters and eventually merges into the North Equatorial Current (Mittelstaedt, 1991). The interaction between this upwelling and the large scale ocean currents allows the cold, upwelled water to be advected farther offshore and southward (Mittelstaedt, 1991). This structure of ocean currents produces a frontal zone in the SST field off the coast of Mauritania during summer. We postulate that the variability of SST along the West African coast, associated with upwelling, may have a profound influence on the development of tropical cyclones in the eastern Atlantic.

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