Seasonal forecasting of thailand summer monsoon rainfall

This paper describes the development of a statistical forecasting method for summer monsoon rainfall over Thailand. Predictors of Thailand summer (August-October) monsoon rainfall are identified from the large-scale ocean-atmospheric circulation variables (i.e. sea-surface temperature and sea-level pressure) in the Indo-Pacific region. The predictors identified are part of the broader El Nino southern oscillation (ENSO) phenomenon. The predictors exhibit a significant relationship with the summer rainfall only during the post-1980 period, when the Thailand summer rainfall also shows a relationship with ENSO. Two methods for generating ensemble forecasts are adapted. The first is the traditional linear regression, and the second is a local polynomial-based nonparametric method. The associated predictive standard errors are used for generating ensembles. Both the methods exhibit significant comparable skills in a cross-validated mode. However. the nonparametric method shows improved skill during extreme years (i.e. wet and dry years). Furthermore, the models provide useful skill at 1-3 month lead time that can have a strong impact on resources planning and management. Copyright (c) 2005 Royal Meteorological Society.