Rapid northward progress of monsoon over India and associated heavy rainfall over Uttarakhand: A diagnostic study and real time extended range forecast

Abstract

The unusual features of monsoon over India during 2013 was it’s rapid progress northward from southern tip of India after normal onset on 1st June. The monsoon covered entire India by 16 June and it witnessed very heavy rainfall in June over many parts of northern India in general and Uttarakhand meteorological subdivision in particular, leading to large scale destruction of life and property. In the present study the diagnostic features associated with this unusual behaviour of rapid progress of monsoon is analysed. The performance of the real-time extended range forecasts based on coupled model outputs is also analysed. The latest coupled model from NCEP (the climate forecast system version 2; CFSv2) with 16 members, Japan Meteorological Agency (JMA) Ensemble Prediction System (EPS) with 50 ensemble members and Multi-model ensemble (MME) forecasts are used for this purpose. The rapid progress of monsoon northward with unprecedented rainfall over north India and particularly over Uttarakhand was associated with the movement of low pressure area leading to the increase in moisture convergence over northern India and juxtaposition with upper level deep westerly trough. The rapid progress of monsoon to Northwest India and associated heavy rainfall over northwest India are captured by both models and MME with JMA model performed slightly better in terms of longer lead time of forecasting the coverage of monsoon to entire India. The JMA model performed better in terms of higher departure of rainfall over Uttarakhand compared to that in CFSv2 model, although, it was also underestimated compared to observation and it could be due to the fact that the interaction of upper level westerly trough with the low level convergence was not captured in the model. However, useful skill of monsoon forecast in the extended range is observed on all India level and also over the smaller domain of northwest India.