Verification of forecasts of IMD NWP based cyclone prediction system (CPS) for cyclones over the north Indian seas during 2013

Abstract

As a part of our effort to meet the specific requirement of the operational forecaster, an objective NWP based Cyclone Prediction System (CPS) was developed and implemented for the operational cyclone forecasting work. The method comprises of five forecast components, namely (a) Cyclone Genesis Potential Parameter (GPP), (b) Multi-Model Ensemble (MME) technique for cyclone track prediction, (c) Cyclone intensity prediction, (d) Rapid intensification and (e) Predicting decaying intensity after the landfall. GPP is derived based on dynamical and thermo dynamical parameters from the model output of IMD operational Global Forecast System. The MME technique for the cyclone track prediction is based on multiple linear regression technique. A Statistical Cyclone Intensity Prediction (SCIP) model for predicting 12 hourly cyclone intensity (up to 72 hours) is developed applying multiple linear regression technique. For forecast of inland wind after the landfall of a cyclone, an empirical technique is developed. This paper describes the development strategy of the CPS and performance skill of the system during 2013 for seven cyclonic disturbances. The performance evaluation shows that the GPP analysis at early stages of development of a low pressure system was able to indicate the potential of the system for further intensification. The 12 hourly track forecast by MME (with error 68 km at 12 hr to 187 km at 120 hr), and intensity forecast by SCIP model (with error 5.9 kt at 12 hr to 19.8 kt at 72 hr) are found to be consistent and very useful to the operational forecasters. The probabilistic rapid intensification forecasts are found to be skillful compared to climatology. The error statistics (11 kt at 6 hr to 6 kt at 24 hr) of the decay model shows that the model could predict the decaying intensity after landfall with reasonable success. The performance statistics demonstrates the potential of the CPS for improving operational cyclone forecast service over the north Indian Seas.