Real-Time Prediction of the Tropical Cyclogenesis Location over Bay of Bengal Using Global Forecast System (GFS) - Monitoring and Prediction of Tropical Cyclones in the Indian Ocean and Climate Change - page 282

Real-Time Prediction of the
Tropical Cyclogenesis Location
over Bay of Bengal Using
Global Forecast System (GFS)
V.R. Durai* and S.K. Roy Bhowmik
India Meteorological Department, New Delhi - 110003
*e-mail: [e-mail]
1. Introduction
Cyclogenesis of tropical storms has not yet been completely understood, but
these storms develop over five major zones in the Northern hemisphere. Bay
of Bengal (BoB) and the Arabian Sea are two such zones. Cyclones, tropical
disturbances of all intensities with reference to wind speed greater than 33
knots, form in the BoB and in the Arabian Sea almost throughout the year.
They are more frequent in the Bay and in Arabian Sea in the region between
latitude 6ºN and 15ºN during the pre-monsoon and post-monsoon seasons and
are least frequent during the winter. Tropical cyclone formation involves
interaction of a variety of processes, both on the synoptic scale as well as the
mesoscale. Gray (1979) identified several large-scale conditions as necessary
for tropical cyclogenesis, including preexisting low-level relative vorticity and
high mid-tropospheric humidity. Chen and Frank (1993) noted that mesoscale
convective vortices (MCVs) spawned by tropical convection could be a possible
mechanism for forming the initial low-level relative vorticity maximum. This
variety of tropical cyclogenesis mechanisms provides a challenge in identifying
the sufficient conditions for genesis.
Tropical cyclogenesis also continues to be a forecasting challenge. Current
operational models have difficulty accurately forecasting tropical cyclone
formation. This is particularly true for the initial development stages of the
pre-cursor tropical disturbance. Chen and Frank (1993) noted that the process
by which MCVs evolved into tropical cyclones could be divided into two stages:
the genesis stage (formation of mid-level mesoscale vortex) and the
intensification stage (further intensification of this vortex into a tropical