A study of five tropical cyclones in the Bay of Bengal has been conducted to estimate the pressure drop in the eye of the cyclone and associated storm surge height using Doppler velocity data. A new value of constant K (13.637) has been found in the empirical relation Vmax = K�(P-Pc) between maximum velocity (Vmax) and central pressure drop (P-Pc) in terms of maximum radial velocity measured by the Doppler Weather Radar (DWR) for coastal region of India. The present study provides an alternate method for estimating central pressure drop and expected storm surge height associated to a tropical cyclone. The study also reveals that the storm surge height estimated from Doppler velocity measurements for these cyclones is very close to the actual occurrence. The results of pressure drop estimates from Doppler velocity are in close agreement with the satellite estimates. It is also observed that DWR estimates are sometimes better than those from satellite. However, the limitation of DWR is the limited range of observation (400 km) and shorter duration of cyclone tracking.

Thunderstorm and hailstorm are well known short term severe weather phenomena which sometimes turn in to natural hazard especially in Gangetic West Bengal region of India. Large vertical extent of the cumulonimbus cloud, very high reflectivity, squally wind speed sometimes exceeding 100 km/h and heavy rainfall are the main features of these thunderstorms during pre-monsoon period in this region. A study of 70 thunderstorms has been carried out during the pre-monsoon season (March-May) of the year 2005 around Kolkata (22.5° N, 88.5° E) using Doppler Weather Radar and Upper air data. Standard convective indices like CAPE, CINE, LI, BRN and VGP have been evaluated and analyzed statistically. As no definite thresholds of the convective indices are available for thunderstorm prediction in this region, an attempt has been made to find threshold of these indices for possible occurrences of thunderstorms in Gangetic West Bengal region after the analysis of the thunderstorms during year 2005. The validity of these convective indices has been checked with 34 occurrences of thunderstorms during 2006-2007 recorded by Doppler Weather Radar Kolkata. The study reveals that nowcasting of thunderstorms may be done at least 2-3 hrs in advance witha fair degree of accuracy using Doppler radar products only. However, the lead time of nowcasting may be further improved if the convective indices are also analyzed and used in addition to the DWR data. A simple technique has been suggested by the authors for better prediction of thunderstorms at least three to four hours in advance.

This study aims to investigate the impact of the Three-Dimensional Variational (3DVAR) assimilation of Doppler Weather Radar (DWR) wind data together with the India Meteorological Department (IMD) upper air and surface data for the prediction of a tropical cyclone, which formed over the Bay of Bengal. The National Centers for Environmental Prediction Final Analyses (NCEP FNL) data are used to produce initial conditions. Three numerical experiments were designed to study the effect of 3DVAR assimilation. For the first experiment, the model integrations were performed without any assimilation of observations. IMD upper air and surface observations were assimilated using 3DVAR for the second experiment and the third experiment assimilated DWR wind data along with IMD observations. The model results are compared with one another and also with the observations. The results of the study indicate that the assimilation of DWR wind data and IMD data have resulted in improvements in the simulation of strong vertical velocity, higher warm core temperature and strong gradients in the horizontal wind speed as well as improved spatial distribution of the precipitation.

On 12 March 2003 a very severe thunderstorm traversed across the Gangetic West Bengal in India and adjoining areas of Bangladesh. Documentation and analysis of the thermodynamic condition of the atmosphere and evolution, structure and movement of the storm as tracked by the Doppler radar is presented in this paper. One particular cell of the system lasted for over 12 h. Based on the internal structure, reflectivity, duration and weather pattern on the ground, it has been concluded that the particular cell was a supercell.