Typhoon interaction with the Taiwan topography during the Tropical Cyclone Structure—2008 (TCS-08) experiment

During the THORPEX - Pacific Asian Regional Campaign/Tropical Cyclone Structure - 2008 (T-PARC/TCS-08) experiment, two typhoons passed over the island of Taiwan. Typhoon Sinlaku produced widespread flooding with multiple precipitation accumulations in excess of 1000 mm (40 in) and a maximum total of 1611 mm (63.4 in). Two weeks later, Typhoon Jangmi passed over the island producing a maximum precipitation amount of 1125 mm (44.3 in) and a peak wind gust of 62.4 m/s (121.3 kts). The effect of the mountainous terrain of Taiwan on these two storms is examined using numerical simulations with the Naval Research Laboratory's tropical cyclone version of the Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS®-TC).

The initial control simulation of Typhoon Sinlaku produced a relatively accurate track with the exception of an excessive southward deflection upstream of the island, possibly due to the model underestimating the intensity of the storm. This small upstream track error resulted in very large QPF errors between the simulated and observed tracks. When the topography of Taiwan was reduced and eventually removed, the amount of southward deflection lessened and the storm began to recurve upstream of the island. The precipitation amounts over land were greatly reduced due to both the decrease in upslope forcing and the strongest pre-existing convection to the right of Sinlaku's track failing to make landfall. Since Typhoon Jangmi passed over the same area as Sinlaku a short time later, ocean surface processes were important upstream of Taiwan. The effect of terrain on Jangmi's track was less dramatic, but did produce significant differences, especially after the storm had passed over the island. The findings from these two cases are compared to preliminary results from simulations of the record-setting Typhoon Morakot which produced significantly more precipitation and flooding in the season after TCS-08.