Structure of the Regional Heavy Rainfall System that Occurred in Mumbai, India, on 26 July 2005

Abstract

An intense rainfall system that developed on the west coast of India caused heavy rain in excess of 900 mm at Santa Cruz, a suburb of Mumbai, on 26 July 2005. This system was simulated by the non-hydrostatic model (NHM) of the Japan Meteorological Agency (JMA), using the global analysis data of JMA as the initial condition. A maximum rainfall amount exceeding 1,100 mm in 17 hours was obtained by the simulation with a horizontal resolution of 5 km.
The detailed structure of the rainfall system at the intense rain stage was investigated by NHM with a horizontal resolution of 1 km. The rain was mainly caused by a humid westerly flow near the surface, which overrode a cold pool near the mountain range. A dry southwesterly flow at the height of 2.51 km enhanced the cold pool. Another low-level humid westerly flow entered the rainfall system from the north and formed a thick humid northerly flow that reinforced the rainfall.
Sensitivity experiments were conducted to investigate the influences of the mountain range, water vapor of the airflow north of the system, and the dry westerly flow. The results supported the proposed structure of the heavy rainfall system.