Modulation of low-latitude west wind on abnormal track and intensity of tropical cyclone Nargis (2008) in the Bay of Bengal

Tropical cyclone (TC) Nargis (2008) made landfall in Myanmar on 02 May 2008,bringing a storm surge, major flooding, and resulting in a significant deathtoll. TC Nargis (2008) displayed abnormal features, including rare eastwardmotion in its late stage, rapid intensification before landing. Usingreanalysis data and a numerical model, we investigated how a low-latitudewesterly wind modulated TC Nargis' (2008) track and provided favorableatmospheric conditions for its rapid intensification. More importantly, wefound a possible counterbalance effect of flows from the two hemispheres onthe TC track in the Bay of Bengal. Our analysis indicates that a strongwesterly wind burst across the Bay of Bengal, resulting in TC Nargis' (2008)eastward movement after its recurvature. This sudden enhancement of westerlywind was mainly due to the rapidly intensified mid-level cross-equatorialflow. Our results show that a high-pressure system in the SouthernHemisphere induced this strong, mid-level, cross-equatorial flow. During therapid intensification period of TC Nargis (2008), this strong and broadwesterly wind also transported a large amount of water vapor to TC Nargis(2008). Sufficient water vapor gave rise to continuously high and increasedmid-level relative humidity, which was favorable to TC Nargis' (2008)intensification. Condensation of water vapor increased the energy supply,which eventuated the intensification of TC Nargis (2008) to a category 4 onthe Saffir-Simpson scale.