A method of initializing tropical cyclones for high-resolution numerical models

An objective analysis method has been developed at Naval Research Laboratory to analyze tropical cyclone circulations for use with high-resolution model forecasts. The method takes into account the special characteristics of tropical cyclone circulations and the availability of observations near cyclone centers. It is based upon a 3-dimensional multi-variate variational analysis with modifications to include (1) variable analysis length scales to handle multi-scale circulation near tropical cyclone centers, (2) different balance conditions between wind and pressure gradient near cyclone centers, (3) relocation of background cyclone centers to their observed locations prior to the analysis, and (4) synthetic soundings to supplement observations near cyclone centers. The synthetic observations are constructed at constant pressure levels by fitting the observed tropical cyclone wind structure parameters to a Rankin vortex feature model. The relocation of background cyclone centers is achieved by isolating the tropical cyclone circulation from the flow in the environment and then relocating it to its observed location. The analysis length scale near the cyclone center is chosen to be much smaller than that outside the area of the cyclone core. Initial conditions resulting from this analysis method and their impacts on tropical cyclone intensity and track forecasts will be discussed.