Climatology and characteristics of rapidly intensifying tropical cyclones over the North Indian Ocean

Abstract

AbstractRapid intensification (RI) of a tropical cyclone (TC) is defined as an increase in the wind speed by 30 knots within 24 hours. It is a less understood process, particularly for TCs over the North Indian Ocean. We considered data for the past 39 years (1982–2020) from the JTWC and studied the climatology of TCs. We found that, out of 197 cases, 44 TCs (22%) experienced RI. There is a significant increasing trend in RI TCs frequency and duration over the Arabian Sea (AS). Lifetime maximum intensity (LMI) is significantly higher, and genesis to LMI duration is also significantly longer for TCs undergoing RI over the AS. LMI is double for RI TC than for non‐RI (NRI) TC. The longer duration to achieve the higher maximum intensity resulted in a longer total lifespan for RI TCs. All TCs reaching a super cyclonic storm category underwent RI and generally, RI onset happens in the depression stage. The composites are prepared to understand the characteristics of RI TCs in contrast to NRI TCs. For the RI TC composite, the period includes 12 hours before and 24 hours after the RI onset. For the NRI TC, we considered 36 hours starting from the initial intensification stage. The analysis shows the RI TCs are embedded in the warm water regions with ocean heat content of 90–100 kJ · cm−2 and strong latent heat flux transport. RI TCs also have higher positive low‐level relative vorticity, higher upper‐level divergence, and higher mid‐level relative humidity, with higher moisture content around the TC centre. Deep clouds with 208 K < IRBT <240 K dominate in RI TCs. The total surface rainfall for RI cases is symmetric around the centre. RI TCs have higher rainfall fractions with intense surface rain rates for stratiform and convective rainfall during the pre‐monsoon.