GFS Storm Precipitation, 2019 and 2020 Storms

Operational forecast models are necessary for the prediction of weather
events in real time. Verification of these models must be performed to
assess model skill and areas in need of improvement, particularly with
different types of weather events that may occur. Despite the devastating
impacts that can be caused by tropical cyclones (TCs) that undergo
extratropical transition (ET) and become post-tropical cyclones (PTCs),
these storms have not been extensively studied in the context of
short-term weather prediction. This study completes the first analysis of
the Global Forecast System (GFS) and a pre-operational version of the
newly operational Hurricane Analysis and Forecast System (HAFS) models in
forecasting the occurrence of ET and the rainfall associated with ET
storms in the North Atlantic basin. GFS's skill exceeds that of HAFS
in forecasting the occurrence of ET, but HAFS tends to have lower track
and rain rate errors in the fully tropical phase of ET storms' life
cycles. Both models simulate rain rates that are often too high near the
storm center and fail to capture the larger area of moderate rain rates
that greatly contributes to total rainfall accumulation. The discrepancies
in rain rates between the models and IMERG could be attributed to the
models' tendency to keep storms too intense and too compact with an
overly strong warm core, even throughout the ET process.