Analysis of Tropical Cyclone Initialization in COAMPS-TC for Hurricane Patricia (2015) Utilizing TCI Experiment Datasets
Naval Postgraduate School Monterey United States
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From 21 to 23 October 2015, Eastern Pacific Hurricane Patricia underwent a period of extreme rapid intensification that both hurricane specialists and numerical weather prediction NWP models failed to predict, including the Navy operational model for hurricane prediction, the Coupled OceanAtmosphere Mesoscale Prediction System for Tropical Cyclones COAMPS-TC. Fortunately, the Office of Naval Research ONRfunded Tropical Cyclone Intensity TCI initiative collected high spatial resolution in-situ and remotely sensed data during Patricias rapid intensification.In order to understand the relationship between initial conditions and subsequent intensity forecast errors, this study utilizes these datasets to validate the initial conditions in the multiply-nested COAMPS-TC model at three synoptic times and finds three main conclusions. First, the structure of the outflow layer in the COAMPS-TC initial conditions at 1800 UTC 22 and 23 October did not include an observed equatorward outflow jet. Second, the maximum winds of the COAMPS-TC model vortex at 1800 UTC 21 October were too weak. Finally, the initial vortex in the COAMPS-TC model at 1800 UTC 22 October had a radius of maximum winds that was too large, a warm core too low in elevation, and an outer circulation where the winds were too strong. While other factors may have contributed to the intensity forecast errors for Patricia, this study indicates it is likely that the initial condition errors contributed significantly, and illustrates the need for sophisticated data assimilation systems that can ingest high-density observations in order to improve TC intensity forecasting.