Unusual tracks:Statistical,controlling factors and model prediction

The progress of research and forecast techniques for tropical cyclone(TC)unusual tracks(UTs)in recent years is reviewed.A major research focus has been understanding which processes contribute to the evolution of the TC and steering flow over time,especially the reasons for the sharp changes in TC motion over a short period of time.When TCs are located in the vicinity of monsoon gyres,TC track forecast become more difficult to forecast due to the complex interaction between the TCs and the gyres.Moreover,the convection and latent heat can also feed back into the synoptic-scale features and in turn modify the steering flow.In this report,two cases with UTs are examined,along with an assessment of numerical model forecasts.Advances in numerical modelling and in particular the development of ensemble forecasting systems have proved beneficial in the prediction of such TCs.There are still great challenges in operational track forecasts and warnings,such as the initial TC track forecast,which is based on a poor pre-genesis analysis,TC track forecasts during interaction between two or more TCs and track predictions after landfall.Recently,artificial intelligence(AI)methods such as machine learning or deep learning have been widely applied in the field of TC forecasting.For TC track forecasting,a more effective method of center location is obtained by combining data from various sources and fully exploring the potential of AI,which provides more possibilities for improving TC prediction.

Numerical tests for tropical cyclone track prediction by the global WRF model

This work use the global WRF model containing quadruply nesting with which the highest resolution reached 10 km to simulate the typhoons landed on the coast of China in 2011.The model is driven by the reanalysis data fnl with the resolution of 1°x 1°.The study assess the feasibility and applicability of the global WRF model in the 1-7 days prediction of Tropical Cyclone(TC)track by comparing it with the regional WRF model containing the same setting(physical scheme,dynamical frame,model resolution and nesting grid domain).The global model obtain a similar forecast accuracy to the regional model in 1-7 days,with a difference less than 50 km.The forecast accuracy of the global model for 1,2,3,4,5,6 and 7 days is about 70 km,120 km,180 km,240 km,320 km,400 km,and 500 km,respectively.The reason of the significant TC track errors in the forecast more than 3 or 4 days is analyzed,it is due to the poor representation of typhoon and its steering flow under the situation of binary typhoon system.The study show that the global WRF model can be exploited to proceed the high resolution TC simulation and make the TC track forecast up to 7 days but not in the case of multiple typhoon.