A regional nonhydrostatic mathematical model of the wind system of the lower atmosphere, developed recently in the Polar Geophysical Institute, is utilized to investigate the initial stage of the origin of large-scale vortices at tropical latitudes. The model produces three-dimensional distributions of the atmospheric parameters in the height range from 0 to 15？km over a limited region of the Earth’s surface. Time-dependent modeling is performed for the cases when, at the initial moment, the simulation domain is intersected by the intertropical convergence zone (ITCZ). Calculations are made for various cases in which the initial forms of the intertropical convergence zone are different and contained convexities with distinct shapes, which are consistent with the results of satellite microwave monitoring of the Earth’s atmosphere. The results of modeling indicate that the origin of convexities in the form of the intertropical convergence zone, having distinct configurations, can lead to the formation of different large-scale vortices, in particular, a cyclonic vortex, a pair of cyclonic-anticyclonic vortices, and a pair of cyclonic vortices, during a period not longer than three days. The radii of these large-scale vortices are about 400–600？km. The horizontal wind velocity in these vortices can achieve values of 15–20？m/s in the course of time. 1. Introduction It is known that severe tropical cyclonic storms and hurricanes can cause tremendous damage and numerous fatalities. Therefore, prediction of tropical cyclone formation is a very important problem. Despite considerable efforts, the physical theory of tropical cyclone formation is still far from completion, even if some aspects of tropical cyclogenesis are commonly understood, in particular, in the late stages of formation as well as in a fully developed stage (see [1–4] and references therein). For tropical storm forecasting, it is necessary to investigate the pregenesis evolution of tropical cyclone. This investigation assumes that physical aspects of tropical cyclone formation must to be studied. To investigate physical mechanisms responsible for the tropical cyclone formation, mathematical models may be utilized. Most of numerical studies of tropical cyclogenesis explore how a tropical cyclone forms from vortices, those are precursors to tropical cyclones, or from other preexisting large-scale disturbances of the troposphere [5–12]. In the Polar Geophysical Institute (PGI), the nonhydrostatic model of the global wind system in the Earth’s atmosphere has been developed not long ago [13, 14].
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