A tropical cyclone analysis system for COAMPS-TC

COAMPS-TC is a version of the Coupled Ocean and Atmosphere Mesoscale Prediction System (COAMPS®) that has been developed for tropical cyclone (TC) track and intensity forecasts. Among other improvements to COAMPS-TC, we have upgraded the NRL Atmospheric Variational Data Assimilation System (NAVDAS) to better analyze the structure and intensity of tropical cyclones. The upgrades include a variable analysis length scale to handle multi-scale circulations in tropical cyclones, vortex relocation to correct the position errors of background tropical cyclones, and moving-grid update cycling to manage data assimilation for storm following inner meshes. The variable analysis scale is gradually reduced toward the center of the TC to analyze the smaller scale circulation near the center. The vortex relocation moves background tropical cyclones to their observed locations without generating discontinuities in the background fields. The moving-grid update cycling determines the configuration of the inner meshes for TC analysis based upon the grid movement history and update cycle time interval, and then moves the grid centers to be collocated with selected TC centers within the first 6 hours of the forecast. The vortex relocation significantly reduces the background errors of the TC analysis. The moving-grid update cycling maintains the high-resolution structure of the tropical cyclones in the background fields thereby improving the TC structure and intensity analysis. This paper will describe this TC analysis system and demonstrate its performance.