Two modes of tropical cyclogenesis were identified and simulated in an idealized environment using a three-dimensional, full physics model (MM5V1). One mode is the in situ formation/development of tropical disturbances throughthe breakdown of a continuous ITCZ. Another mode is the formation/development of tropical disturbances far away from (about 10 degrees north of) the continuous ITCZ, which is related to the formation of the upper level vortices