65th IHC Booklet/Program (pdf - 4.9MB) - Office of the Federal ...

Evaluation and Development of Ensemble Prediction System for the Operational HWRF
Model
Zhan Zhang, V. Tallapragada, R. Tuleya, Q. Liu, Y. Kwon, S. Trahan, J. O’Connor, and W. M.
Lapenta
(zhan.zhang@noaa.gov)
NOAA/NCEP/EMC-IMSG, Camp Springs, MD
Ensemble prediction system (EPS) has been proven to be effective in reducing various
uncertainties in model initial states and model physics, and therefore improving model forecast
skills. This talk reviews the undergoing efforts at NCEP/EMC to develop EPS based on the
operational Hurricane Weather Research and Forecasting (HWRF) model. The study attempts to
understand the impact of various uncertainties on the model hurricane track and intensity
forecasts, and to find out the best combination of ensemble perturbations for HWRF EPS.
The key to a successful hurricane ensemble forecast is to generate a set of ensembles that
represent the uncertainties in hurricane model prediction system. The important uncertainties that
need to be taken into account in hurricane EPS include the uncertainties in the hurricane initial
structures, initial large scale environment flows, model lateral boundary conditions (LBC), and
model physics. Following ensemble perturbations are evaluated within the operational HWRF
model framework:
• Initial hurricane structures: in order to reduce the uncertainties in initial hurricane
structure, the observed initial radius of maximum wind is perturbed by
increasing/decreasing 25% of its value in tcvital file;
• Large scale environment flows and LBC at initial states: data sets from Global Ensemble
Forecast System (GEFS), which have resolution of T190L28 and includes 21 ensemble
members, are used to initialize HWRF domain and LBC;
• Physics-based perturbations: uncertainties due to model physics can be reduced by using
various physics packages in HWRF. Several model physics packages have been used for
this purpose. They include two convective schemes: Simplified Arakawa-Schubert
(SAS), Kain-Fritsch, and two PBL schemes: GFS PBL scheme, MYJ PBL scheme.
• Combined ensemble perturbations: all above ensemble forecasts are then combined to
construct one ensemble.
Forecast experiments of three hurricanes in 2010 season, Earl, Alex, and Celia, are carried out
for different ensemble configurations. The track and intensity forecasts from each subset of
ensemble are evaluated and compared. Different combinations of ensembles are examined to
find out the best results for HWRF EPS. Various probabilistic forecast products resulted from
EPS, such as track striking probability, ensemble track spread, are also discussed.
Session 6 – Page 5