Since the Asian Monsoon brings significant rainfall to the wider Southeast Asia region and its neighboring countries, it is hugely important to the billions of people in the region for their agriculture, economy and livelihoods. When the Asian Summer Monsoon starts anomalously early or late in some years, It could cause floods/droughts, resulting in the disruption of agricultural production, even displacement of inhabitants. In addition, the extraordinary late monsoon onset leads to an extended length of high sea surface temperature, and thus increasing the risk of coral bleaching, as is the case in 1998, 2010 and 2016. It is vital for countries in the region to improve the monitoring capability on monsoon onset in the wider Southeast Asia region for societal and ecosystem benefit.