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IOC Sub-Commission for the Western Pacific (WESTPAC)

Advancing knowledge and cooperation for a healthy ocean and prosperous society

Our Programme

Monsoon Onset Monitoring

What is it?

A monsoon is a tropical and subtropical seasonal reversal in wind direction and associated precipitation, which is the result of the differential heating of a continent-scale landmass and the adjacent ocean. Monsoonal climates are characterized by a dramatic seasonal change in direction of the prevailing, or strongest, winds over a region, which brings a remarkable change in rainfall and leads to distinct wet and dry seasons throughout much of the tropics and subtropics.

Why is it important to us in the region?

Asia experiences the vigorously changing monsoon climate. The Asian Monsoon, as the most active monsoon system, plays a key role in the spatial distribution and strength of rain belt in Asia, and has great influences on the weather and climate of most Asian countries.

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.

What we do?

In view of the fact that the Asian Monsoon is evidently influenced by and coupled with the ocean, the IOC Sub-Commission for the Western Pacific (WESTPAC) initiated in 2009 one pilot project entitled “Monsoon Onset Monitoring and its Social and Ecosystem Impact” (MOMSEI) within its South East Asia Global Ocean Observing System (SEAGOOS), with a focus to understand the preconditioning role of ocean in monsoon onset in order to improve forecasting the Asian monsoon onset and its multi-scale variability.

Since 2009, WESTPAC/MOMSEI has been carrying out large-scale observations over the Andaman Sea and eastern Indian Ocean to investigate the critical ocean-atmosphere interactions, as well as the impacts of monsoon anomaly on the massive coral reef bleaching in the Andaman Sea and the eastern Indian Ocean upwelling variations along Java-Sumatra coast.

WESTPAC assists its Member States advancing ocean knowledge and enhancing their capacities for monsoon onset monitoring, through cruises, workshops, student/professional exchanges, and summer schools, as well as informs management actions to prepare for and mitigate the impact of coral bleaching caused by the delayed monsoon onset.


Field Survey in Andaman Sea and Eastern Indian Ocean

Science and Capacity Development

Research updates and publications

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How to cite articles on the website?

The following are examples of how to cite articles on this website:

Web page with known publication date

WESTPAC. Monsoon onset monitoring: What is it?. IOC Sub-Commission for the Western Pacific website,, 27/09/22.

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WESTPAC. Monsoon onset monitoring: What is it?. IOC Sub-Commission for the Western Pacific website,, accessed on 27/09/22.

Field Survey

The SEAGOOS program works to establish several pilot ocean forecasting systems for selected subdomains including the Andaman Sea (Thai’s waters) and the Malaysian East Peninsula Continental Shelf, for high resolution development.