Evaluation of Tropical Cyclone Formation and Track Forecasts from the ECMWF 15-day and 32-day Ensemble for the western North Pacific

The European Center for Medium-range Weather Forecasts (ECMWF) made available daily 15-day, and weekly 32-day, 51-member ensemble forecasts of western North Pacific tropical cyclone formations and tracks in support of the Impact of Typhoons on the Ocean in the Pacific (ITOP) field experiment during August to October 2010.

In all analysis-forecast sequences, model-derived variables that are related to tropical cyclone formation have been extracted for each trackable tropical system. Specific parameters include location, vertical wind shear, warm core magnitude, moisture conditions, vorticity, and sea-level pressure. The utility associated with the use of these variables for probabilistic forecast of tropical cyclone formation will be examined. Additionally, the reliability of the model in forecasting tropical cyclone genesis at short (days 1-3), medium (days 4-8) and long term (days 9-32) periods will be reported at the meeting.

Secondly, a process was also developed to create ensemble weighted mean vector motion tracks to generate forecast tracks that were comprised of individual ensemble member tracks for the longer term (days 9-32) period. In post-season analysis, some techniques (lagged-in-time, pre-processing and/or post-processing, etc.) are being examined to improve the accuracy and the reliability of these tracks. The outcome of these developments will also be reported at the meeting.