Environmental conditions leading to spinup and intensi cation during the 2008 West Paci c tropical cyclone season

The large-scale features favoring tropical cyclogenesis and development are low vertical wind shear, below normal sea-level pressure and abnormally warm ocean temperatures. High wind shear is thought to inhibit development by preventing cumulonimbus condensation from collecting into a distinct heat source at the core of a disturbance. Also, it shears the initially delicate pattern of circulation created by azimuthal winds, which are forced into cyclonic rotation by the Coriolis and pressure gradient forces. Low surface pressure assists this process by e ecting an in ow into the core region in order to drive radial winds that pick up heat and moisture from the air/sea interface.