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On the Genesis and Intensification of Hurricanes

Special talk by Gilbert Brunet, ECCC and McGill University

In general, observations indicate that only a small fraction in a fixed framework (from 140° W to 20° E) covering African to the eastern Pacific regions of the easterly waves that occur in a single hurricane season contribute to tropical cyclogenesis. However, this small fraction includes a large portion of named storms. In addition, a study by Dunkerton et al. (2009) has shown that named storms in the Atlantic and eastern Pacific basins are almost all associated with wave breaking of a tropical easterly waves. We will discuss fundamental dynamical and physical processes related to hurricane genesis. We will show that the coexistence of an African easterly wave that is breaking and a region of weak meridional potential vorticity (PV) gradient over several days might be a major factor determining whether or not tropical disturbances develop into hurricanes. This finding answered the long-standing question of why only a small fraction of African easterly waves contribute to hurricane genesis.