A study of rapid intensification of tropical cyclone Ockhi using C-band polarimetric radar

Tropical cyclone Ockhi (2017) had a very unusual track with unprecedented rapid intensification (RI) and dynamical evolution. During its early phases, a C-band polarimetric Doppler Weather Radar (DWR), installed in Thiruvananthapuram, Kerala, continuously monitored it. The present study focuses on the observations and analysis of the extremely tall precipitation features overshooting Troposphere, called hot towers, prior to and during the RI stages of Ockhi. The maximum height of such features within the inner core exceeded 20 km, with the maximum observed areal coverage over 800 km2. The peak convective burst (CB) activity was seen 9–12 h prior to the onset of RI of Ockhi. The differences among the Maximum Sustained Wind speed (MSW) and Mean Sea Level Pressure (MSLP) obtained from various best track data sets were in the range 5–25 knots and 1–28 hPa, respectively, with the maximum difference seen during the CB phase. Ockhi also exhibited differential reflectivity enhancements, often collocated with the hot towers. Further, we investigated upper ocean Tropical Cyclone Heat Potential (TCHP), derived from the Global Temperature and Salinity Profile Programme (GTSPP) profiles. During the peak CB activity, the TCHP was around 121 kJ cm−2, almost 50 kJ cm−2 higher than the climatological mean of that area. Significant drop in TCHP was observed in the next 24 h concurrent with the RI. The radar-based observations of the hot towers in conjunction with the TCHP and other relevant ocean parameters could prove to be valuable indicators in predicting the RI phase of the storms and gaining a better insight for estimating the damage potential of the cyclones.