Applications of Weighted Track Analog Intensity Prediction Scheme for Western North Pacific Tropical Cyclones

APPLICATIONS OF A WEIGHTED TRACK ANALOG INTENSITY PREDICTION SCHEME FOR WESTERN NORTH PACIFIC TROPICAL CYCLONES

Hsiao-Chung Tsai Russell L. Elsberry Department of Meteorology Trauma, Health, & Hazards Center Naval Postgraduate School University of Colorado, Colorado Springs

The situation-dependent intensity prediction (SDIP) technique of Elsberry and Tsai (2014) has been extended for use as an operational intensity prediction technique and to provide an intensity spread guidance. In the first step of searching for the 10 best historical track analogs to match the JTWC forecast track, more weight is given to the 72-h to 120-h period so that if a landfall is being predicted, a higher rank is assigned to those potential analogs that have a similar landfall. A weighted analog intensity (WANI) prediction scheme is then developed by using the weighting factors defined by the inverse track difference. As was the case for the SDIP technique, the WANI has the intensity prediction skill relative to the present method (ST5D) in almost all of the sub-regions, but especially for forecast tracks near the Philippines, Taiwan, Japan, Southeast Asia, and South China Sea. In addition, reliable intensity spread guidance is provided by these 10 best historical analogs after accounting for the intensity bias and a calibration of the raw intensity spread. The second application of the WANI technique is to improve the intensity forecasts of the 5-day ECMWF ensemble that are available in near-real time on the TIGGE website. Tsai and Elsberry (2013, Geophysical Research Letters) have demonstrated the reliability of selecting those track clusters with at least 70% of the ensemble members as having a more accurate track than the ensemble mean track. It is well-known that a relatively coarse-mesh ensemble is not capable of predicting the actual intensity. Thus, the WANI technique is separately applied to each track cluster within the ECMWF 5-day ensemble to provide an intensity forecast corresponding to that specific track cluster forecast versus the ensemble mean track. The skill and reliability of the intensities for the dominant track cluster versus that for the ensemble mean track are evaluated in terms of the mean absolute errors (MAEs) and biases. Also, the relationships between the ensemble track cluster probabilities and MAEs, and the probability of detection at different forecast times, will be presented. Since WANI can be extended beyond 5 days given any longer track forecast, a third application is to generate intensity forecasts for the tropical cyclone events predicted in the twice-daily ECWMF 15-day ensemble predictions. Thus, an intensity forecast can be generated for the entire life cycle of these tropical cyclone events as soon as they appear in the ECMWF ensemble forecasts.