Analysis of the Cyclonic Vortex and Evaluation of the Performance of the Radar Integrated Nowcasting System (RaINS) During the Heavy Rainfall Episode which caused Flooding in Penang, Malaysia on 5 November 2017

Abstract

ABSTRACT: Even though Malaysia is relatively safe from the direct path of tropical cyclones nevertheless the passage of such systems over the neighbouring seas and their tail effect present a unique challenge for forecasters. In rare situations, tropical cyclones had made landfall on Malaysian shores such as Typhoon Vamei in 2001 and Tropical Storm Greg in 1996. Hence it is vital to forecast the severity of the heavy rainfall events associated with low pressure systems to assist the disaster management agencies in decision making. Towards this endeavour, the Malaysian Meteorological Department (MMD) utilises a nowcasting system called Radar Integrated Nowcasting System (RaINS) which uses a combination of radar data and Numerical Weather Prediction (NWP) data. RaINS was adapted from SWIRLS (Short-range Warning of Intense Rainstorms in Localised Systems) developed by the Hong Kong Observatory (HKO) and operationalised in MMD in August 2017. This paper studies the cyclonic vortex and synoptic features during the heavy rainfall event that caused major flooding in Penang, Malaysia on 5 November 2017. This paper also investigates the performance of RaINS in predicting the rain cloud distribution and intensity during that event. It is found that RaINS is capable of forecasting the rain cloud distribution and intensity reasonably well in the very short-term period of 1-3 hours. The forecasts are verified by comparing the RaINS forecast data with observed radar echo. Keywords: cyclonic vortex, RaINS, NWP, SWIRLS, Penang