Warm ocean anomaly, air sea fluxes, and the rapid intensification of tropical cyclone Nargis (2008)

On 2 May 2008, category‐4 tropical cyclone Nargis devastated Myanmar. It was observed that just prior to its landfall, Nargis rapidly intensified from a weak category‐1 storm to an intense category‐4 storm within only 24 h. Using in situ ocean depth‐temperature measurements and satellite altimetry, it is found that Nargis' rapid intensification took place on a pre‐existing warm ocean anomaly in the Bay of Bengal. In the anomaly, the subsurface ocean is evidently warmer than climatology, as characterized by the depth of the 26°C isotherm of 73–101 m and the tropical cyclone heat potential of 77–105 kj cm−2. This pre‐existing deep, warm subsurface layer leads to reduction in the cyclone‐induced ocean cooling, as shown from the ocean mixed layer numerical experiments. As a result, there was a near 300% increase in the air‐sea enthalpy flux to support Nargis' rapid intensification.