A vortex isolation and removal algorithm for numerical weather prediction model tropical cyclone applications

Inserting an externally defined (i.e., synthetic) tropical cyclone (TC) vortex into numerical weather prediction (NWP) model analyses requires that an existing TC vortex first be removed. Similarly, statistical‐dynamical forecasting methods require that the larger‐scale environmental attributes of the flow be separated (and preserved) from those on the smaller meso‐ and TC vortex scales. The existing operational methods to accomplish such tasks are optimized particularly for the respective models grid spacing resolution and thus are not general when applied to finer resolution analyses. Further, the existing methods often adhere to rigid assumptions regarding the size and structure of the TC. A methodology is provided in this study to overcome these limitations. This is accomplished through analyzing the features of the NWP model analysis (e.g., the variables in the vicinity of the TC) and then systematically removing the TC through the application of both a smoothing operator and a subsequent statistical evaluation of the smoothed analysis variable. The value of our methodology is determined when analyzing the results from experiments initialized from an analysis containing TCs and those initialized from analyses without the respective TCs. This methodology is also robust for it does not require a tuning of parameters relative to varying grid‐spacing resolutions and may thus benefit the statistical‐dynamical TC intensity prediction schemes. Key Points Isolate and remove tropical cyclones from prognostic variable fields Estimate the environment surrounding and underlying a tropical cyclone