Evaluation of the Outstanding Track Performance of the GFDL SHiELD
Global Model During the 2021 Atlantic Hurricane Season
Abstract
The 13 km SHiELD (System for High-resolution prediction on
Earth-to-Local Domains) global model that is under development at the
Geophysical Fluid Dynamics Laboratory (GFDL) and runs in near real time,
produced outstanding tropical cyclone track forecasts during the 2021
Atlantic hurricane season, compared to both the upgraded National
Weather Service Global Forecast System (GFSv16), the Hurricane Weather
Research and Forecasting (HWRF) model and the European Centre for
Medium-Range Weather Forecast Integrated Forecasting System (IFS).
SHiELD’s average track forecast errors were 10% and 15% less than the
GFSv16 and HWRF, respectively, for the 3-5 day forecast lead times.
SHiELD’s track forecast skill was comparable to the National Hurricane
Center’s official forecast at several forecast lead times, and
approached 70% skill relative to the Climatology and Persistence Model
(CLIPER) at 3 and 4 days. Similar improvements were found in the western
Pacific basin in 2021, with improvements also seen in the eastern
Pacific at days 4 and 5. Improved performance was also found in the 2019
Atlantic hurricane season, with neutral performance in 2020, when SHiELD
was run retrospectively from the GFSv16 initial conditions. Distribution
of the spatial errors and biases showed that in both the 2021 Atlantic
hurricane season and the previous two years, the largest track forecast
errors from both SHiELD and GFSv16 occurred in the subtropical eastern
Atlantic, associated with a distinct northeast bias. Analysis indicated
that some of the excessive north bias in the GFSv16 is associated with
lower geopotential height fields compared to those in SHiELD.