The Winter Rainfall of Malaysia

Abstract

Abstract Malaysia is geographically separated into Peninsular Malaysia and west Borneo. The rainfall maximum in the former region occurs during November–December, whereas that in the latter region occurs during December–February. This difference of maximum rainfall period indicates that the formation mechanism is different for the rainfall centers in these two parts of Malaysia. Since rainfall is primarily produced by severe weather systems, the formation of a climatological rainfall center is explored through synoptic activity and the rainfall amount of this center is estimated through contributions by rain-producing disturbances. The major cause of the rainfall maximum of Peninsular Malaysia is cold surge vortices (CSVs) and heavy rainfall/flood (HRF) events propagating from the Philippine area and Borneo. In contrast, the major cause of the rainfall maximum of Borneo is these rain-producing disturbances trapped in Borneo. Disturbances of the former group are formed by the cold surge flows of the Philippine Sea type, whereas disturbances of the latter group are formed by cold surge flows of the South China Sea (SCS) type. The population of HRF events is about one-fourth of the rain-producing disturbances in both Peninsular Malaysia and Borneo, but they produce less than ~60% rainfall for these two regions. It is revealed from the synoptic and dynamic analyses that the major Borneo rain-producing disturbances propagate westward before December by strong tropical easterlies, but they are trapped after December by strong northeasterlies of the SCS-type cold surge flow.