Understanding the Tropical Cyclone Gonu

Abstract

Tropical cyclones are non-frontal synoptic-scale warm-core low-pressure systems that originate over the tropical or subtropical oceans and contain organized deep convection and a well-defined cyclonic surface wind circulation. Tropical cyclones form over warm ocean waters, which supply energy to the atmosphere in the form of latent and sensible heat. Under favorable atmospheric thermodynamical conditions associated with low-level convergence a surface low develops into a cyclonic storm. The movement of the tropical cyclone is generally known by the knowledge of the upper atmospheric conditions and the prevailing circulations. Based on intensity, tropical cyclones in the Atlantic, Eastern, and Western Pacific are classified as a tropical depression for a weaker system with V _max≤ 17 m/s ($\approx$62 km/h), a tropical storm for a moderate system with 18 m/s ≤ V _max ◆ 32 m/s, and a hurricane or typhoon for a strong system with V _max ≥ 33 m/s. Hurricanes are called major hurricanes when V _max ≤ 50 m/s and typhoons are classified as super typhoons when V _max ≤ 67 m/s. The maximum wind speed of a strong tropical cyclone may exceed 100 m/s, which may produce storm surge by driving an ocean rise of several meters along the coast. On the average about five tropical cyclones occur annually over the Bay of Bengal (Bhaskar Rao DV, Ashok K (1999) in the north Indian Ocean, which contributes 6% of the global annual frequency. Based on the maximum sustained winds associated with the system and geographical location of their occurrences, they are classified as depression, tropical storm, severe cyclone, or hurricane (Asnani 1993). There are two cyclone seasons in the north Indian Ocean, viz., pre-monsoon (especially May) and post-monsoon (October and November). A few cyclones can also form in the transitional monsoon months, June and September (i.e., arrival and withdrawl phase of the Indian summer monsoon).