South Asian Summer Monsoon: SST-Based Predictability and Real-Time Forecast of the 2016 and 2017 Monsoon

Accurate and timely forecasts of summer monsoon rainfall are of great value to the agrarian economies of the resource stressed and densely populated South-Southeast Asian region. Experimental forecasts of seasonal rainfall are developed using influential climate system components, such as sea surface temperature (SST), whose large thermal inertia and reliable long-term observational record are exploited in the prediction effort. The distinctive feature of this forecasting strategy is its consideration of SST evolution in addition to the usual consideration of SST spatial structure.

The summer monsoon rainfall forecast proceeds with the projection of the antecedent multi-season SST anomalies on the recurrent modes of spatiotemporal variability of seasonal SSTs in the 20^th century (1900-2015); the modes were obtained from an extended-EOF analysis (following Guan and Nigam 2008) of global SSTs. As the multi-season SST anomaly is centered several seasons prior to the forecast period (summer season), the obtained SST principal components are multiplied by their multi-season-lagged seasonal rainfall regressions, generating the summer (June-September) monsoon rainfall forecast. We show that focusing on the multi-season SST structure leads to a discriminating analysis and facilitates forecast of the monsoon rainfall distribution.

The prediction is based on the influence of global SSTs on the South-Southeast Asian monsoon. The skill of the SST-based statistical forecast establishes the bar – an evaluative benchmark – for the dynamical prediction of summer monsoon rainfall.