Creation of a Statistical Ensemble for Tropical Cyclone Intensity Prediction

The Logistic Growth Equation Model (LGEM) and the Statistical Hurricane Intensity Prediction Scheme (SHIPS) model are two statistical-dynamical intensity guidance models currently in operational use at the National Hurricane Center (NHC). LGEM has been a top-performing operational intensity guidance model since its introduction in 2006, while SHIPS has been continually updated since its introduction in 1991 to remain a high-performing operational intensity guidance model. SHIPS employs a multiple-regression technique, while LGEM uses a version of the growth equation. Both models rely on large-scale environmental predictors as input to forecast the change in tropical cyclone intensity, using the official forecast track to derive the predictors from the Global Forecast System (GFS) model fields.

SPICE (Statistical Prediction of Intensity from a Consensus Ensemble) has been developed as a combination of the official SHIPS and LGEM intensity guidance, as well as SHIPS and LGEM runs based off the large-scale environments in the GFDL and HWRF regional models. The six total forecasts are combined into two unweighted consensuses: one from the three SHIPS forecasts and one from the three LGEM forecasts. The two unweighted consensuses are then combined into one weighted consensus, with the weights determined empirically from the 2008-2010 official SHIPS and LGEM sample. These weights favored the SHIPS consensus in the early time periods, shifting to the LGEM consensus being weighted more heavily after about 36 hours.

Retrospective tests of SPICE over the 2008-2010 Atlantic hurricane seasons indicated that SPICE outperformed both SHIPS and LGEM at all lead times, and the improvements were statistically significant at almost all times. SPICE was run real-time during the 2011 season as part of the Hurricane Forecast Improvement Project (HFIP), and results from the season will be presented here. Experiments with using COAMPS-TC, additional regional and global models, and a variable consensus will also be considered.

DISCLAIMER: The views, opinions, and findings in this report are those of the authors and should not be construed as an official NOAA and/or U.S. Government position, policy, or decision.