Analysis of Hurricane Rita (2005) Track Forecasts using Ensemble Reforecast Data

Hurricane Rita was an intense tropical cyclone that developed over the western North Atlantic on 18 September 2005. Rita moved westward and intensified to Category-5 strength on the Saffir-Simpson scale over the central Gulf of Mexico on 22 September. Rita subsequently weakened to Category-3 as it turned northwestward and made landfall on the Texas-Louisiana border on 24 September. At its most intense phase near 0000 UTC 22 September, Rita deepened to 895 hPa, and operational track forecasts indicated a significant threat for Houston, Texas in the 24-72 hour time frame. All of the operational numerical guidance had a distinct left-of-track error, however, as the observed track of Rita fell along the extreme right side of the multi-model and NCEP Global Forecast System ensemble (GEFS) of track forecasts. The aim of this presentation is to utilize NOAA's second-generation global medium-range ensemble reforecast dataset (same configuration as the 2012 version of the NCEP GEFS) to examine the factors that contributed to the systematic short- to medium-range left-of-track forecast error for Rita. We will also place these forecast errors into context by examining a 26-year climatology of track forecast errors over the Gulf of Mexico from 1985–2010.

Emerging results show that the left-of-track forecast errors for Rita were linked to the structure of the subtropical ridge over the southeast U.S. and the evolution of an upper-level cyclonic PV anomaly located west of Rita. Ensemble members that steered Rita on a westward (northwestward) course were characterized by a relatively strong (weak) subtropical ridge over the southeast U.S. and a less (more) amplified subtropical waveguide over the Mexican Plateau and Gulf of Mexico. Errors in the southeastern U.S. subtropical ridge appear to be linked to a wave train emanating from the eastern North Pacific; an error that is systematic in the GEFS reforecasts during 1985–2010 and likely contributes to a climatological left-of-track error over the Gulf of Mexico. Errors in the amplitude of the subtropical waveguide appear to be linked to errors in the bulk upscale effect of convection associated with Rita.