On the separation of upper and low-level centres of tropical storm Kong-Rey (2013) near Taiwan in association with asymmetric latent heating

Tropical Storm (TS) Kong-Rey (2013) moved northward off the eastern coast of Taiwan in late August. Satellite and radar observations indicated an asymmetric convective structure to the south and southwest of the typhoon centre. The maximum rainfall produced was also far from its centre and unlike the usual pattern in climatology, causing flooding, inundation, and casualties in southwestern Taiwan. Moreover, as a detached centre in the middle and upper levels moved over land, a highly tilted vertical structure was revealed and its cause is the focus of the present study. Even though vertical wind shear was present and might cause asymmetry in convective pattern at an early stage, the detachment of the centre aloft during the period of interest (28–29 August) is found to link to Taiwan's steep topography through model experiments and potential vorticity tendency diagnosis. With the uplifting of strong low-level westerly flow by the topography, the intense convection in the control experiment is concentrated at the windward slopes (in southwestern Taiwan) and the wave-number-1 motion vector from the diabatic heating produces southwestward movement of the centre aloft, and thus leads to the detachment. On the other hand, in the sensitivity test without Taiwan terrain, the rainfall region shifts eastward toward the low-level TC centre, and the detachment does not occur. Overall, with a weak vertical coupling of TS Kong-Rey (2013), the impacts of topography can explain both the observed separation of its centres and the unusual rainfall pattern in Taiwan.