Synoptic analysis and mesoscale numerical modelling of heavy precipitation: a case study of flash flood event in Kota Kinabalu, Malaysia

Abstract

A case of severe flash flood event affecting Kota Kinabalu (KK) on 17 Jul 2005 is analyzed by means of synoptic analysis using ERA-Interim Reanalysis and NCEP-FNL Data sets. In the synoptic scale, significant amount of precipitation was recorded in Sabah on 16 Jul and 17 Jul 2005. The heavy rainfall was associated to the upper-level ridge and lower-level cyclone observed over the South China Sea. Several low-pressure centers were also noticed over the Philippines Sea which were believed to intensify the heavy rainfall in Sabah. The vertical cross section for divergence along 116°E at Kota Kinabalu also revealed that a significant convergence was observed near the surface and accompanied by a strong updraft of divergence at upper-level. In the mesoscale, the ability of the convection-permitting WRF model to reproduce the convective cells associated with the heavy rainfall event is examined. A triply nested WRF model with the highest resolution of 5-km horizontal grid spacing was integrated with conventional analysis data. The simulation results were validated against observation from TRMM, CHIRPS, and PERSIANN-CDR. The modelled results agree moderately to the observation and fairly well simulated the initiation, intensification, and deceleration of heavy rainfall at nearly the right time except for some mismatch in terms of spatial distribution. The corresponding precipitation amount was also reasonably reproduced in its distribution but slightly overestimated. We also found that the cause of this severe flash flood is rooted to the prolonged heavy rainfall in the KK region induced by Typhoon Haitang.