HAFS Storm Precipitation and Trajectories, 2020 and 2021

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.

Methods
This dataset includes the data from HAFS in the manuscript "Verification of Operational Forecast Models in cases of Extratropical Transition of North Atlantic Hurricanes" for the analysis of precipitation throughout the entire TC life cycle.

This dataset enables the analysis of precipitation throughout the entire tropical cyclone (TC) life cycle, including points during and after extratropical transition (ET) occurs. The ET process enables TCs to lose their tropical characteristics and be sustained by midlatitude forcing.

The files beginning with "traj_**********" are trajectories for the entire TC and PTC life cycle. TCs are first tracked with TempestExtremes, and these files are the TC trajectories extended using ExTraTrack to include all points during and after ET occurs. Further information about the contents of these files can be found here: https://github.com/zarzycki/ExTraTrack. Finally, the netCDF files (beginning in "masked" and ending in ".nc") contain the isolated TC and PTC precipitation that exceeds the 95th percentile threshold for the model simulations. The 95th percentile varies by location and is calculated from all days, regardless of the presence of rainfall or not, for each set of simulations- historical and future. Precipitation exceeding the 95th percentile is tracked using TempestExtremes, then co-located with TCs and PTCs using a dynamical radius calculated around the trajectories included in this dataset. A full description of the methods can be found in the full manuscript.