Variability of Southwest Monsoon Onset and Withdrawal Dates in East Coast Peninsular Malaysia

The accurate prediction of the onset and withdrawal of the southwest monsoon (SWM) is crucial to the economic and social well-being of the local community whose livelihoods depend strongly on monsoon rains. To date however, there has been a paucity of research into the prediction of SWM timing in east coast Peninsular Malaysia (ECPM) as compared to other monsoon regions. Thus, this study attempts to identify the variability of SWM dates in ECPM and analyze the influence of ENSO on the timing of SWM. Composites of daily 850 hPa zonal winds and outgoing long-wave radiation (OLR) during 2000-2020 were analyzed. The SWM onset is identified by the sudden acceleration of southerly winds in mid-May, while the retreating SWM wind is recognized by the steady decrease of westerly winds through September until October. The average date of SWM onset and withdrawal over ECPM was found to be May 23rd and September 27th, respectively. ENSO has a greater influence on the SWM onset than the SWM withdrawal. The study adds to our understanding of the inter-annual variability of SWM start and retreat dates, laying the groundwork for future research into the impact of climate change on the monsoon timing variability in the study area.