A Comprehensive (Tropical) Cyclone Tracker - Application to Global Model TC Genesis and Intensity Prediction

All model-based TC forecasting schemes require a 'tracker' to locate and analyze both existing (TCs) and pre-formation (pTCs) systems. While a variety of trackers are in use at the operational numerical weather prediction (NWP) centers, all find centers based on well-known synoptic features of TCs, such as maxima in 850 hPa relative vorticity and minima in sea-level pressure. However, these trackers tend to be model and data-format specific, and to be narrowly focused on track and surface wind field prediction.

This paper describes a general and more comprehensive tracker that is a merger of several trackers and diagnostics codes into a single package. The open-source technical implementation generates both the input data and the Fortran read module so as to separate the nitty-gritty details of I/O from the meteorological algorithms and to give fine control over the grid and input model fields. In addition, all control parameters of the tracker are extracted from the code, allowing the user to explicitly control all aspects of the scheme.

As with all operational trackers, this tracker outputs the standard location (latitude/longitude) and parameters of the surface circulation, e.g., maximum 10 m wind speed (TC intensity) and 34/50/64 kt wind radii. The key additional output parameters, that make the tracker comprehensive, are in the 'diagnostic file' -- input to dynamical-statistical TC intensity forecast models LGEM/SHIPS (Logistic Growth Equation Model/Statistical Hurricane Intensity Prediction Scheme). These parameters measure large-scale properties of the cyclone ('storm') and the environment ('sounding'). Beyond the standard diagnostic file parameters, the general tracker calculates a 'user' section with the Hart Cyclone Phase Space and symmetric/asymmetric properties of the 850-200 hPa shear and model precipitation, among others.

The bulk of the talk concerns application to TC genesis and intensity prediction using the operational global NWP modeling systems (deterministic and ensemble) of NCEP, ECMWF and the UKMO. We show that the high-resolution global models circa 2010 not only make excellent track and intensity forecasts but can analyze and forecast preformation TCs, i.e., support the meteorology of 'INVESTS' or the pTCs analyzed by the operational TC forecast agencies (NHC/JTWC).