2. 2018 Hurricane Michael¶

Hurricane Michael was a category 5 hurricane, which made landfall at Florida on October 10, 2018. The peak wind speed and the minimum surface pressure reached to 140 knots and 919 hPa, respectively.

2.1. Model Configuration and Datasets¶

The case runs are initialized at 00z Oct 07, 2018 with 120 hours forecasting. The app uses ./xmlchange to change the runtime settings. The settings that need to be modified to set up the start date, start time, and run time are listed below.

./xmlchange RUN_STARTDATE=2018-10-07,START_TOD=0,STOP_OPTION=nhours,STOP_N=120

Initial condition (IC) files are created from GFS operational dataset in NEMSIO format. The Stand-alone Geophysical Fluid Dynamics Laboratory (GFDL) Vortex Tracker is a tool to estimate hurricane tracks and intensities. The Best Track dataset provides the ‘truth’ data for hurricane evolution.

The GFS model EMC global workflow points to the most up-to-date GFS model development code. The GFS.v16.0.10 is tested in C768 (~13km) resolution and in 128 vertical levels. It uses two scripts, setup_expt_fcstonly.py and setup_workflow_fcstonly.py to set up the mode simulation date and case directories.

The case runs are initialized at 00z Oct 07, 2018 with 120 hours forecasting. The settings that need to be modified to set up the start date and directories are listed below.

./setup_expt_fcstonly.py --pslot Michael --configdir /PATH/TO/YOUR/GLOBAL/WORKFLOW/parm/config --idate 2018100700 --edate 2018100700 --res 768 --comrot /PATH/TO/YOUR/EXP/DIR/comrot --expdir /PATH/TO/YOUR/EXP/OUTPUT/expdir

The account and simulation duration time can be set up in /expdir/Michael/config.base file.

./setup_workflow_fcstonly.py --expdir /PATH/TO/YOUR/OUTPUT/expdir/Michael

Next step is to go to /expdir/Michael to submit the run by

crontab Michael.crontab

2.2. Case Results¶

2.2.1. Hurricane Track and Intensity¶

Hurricane tracks from MRW_GFSv16beta (blue line), MRW_GFSv15p2 (red line), and Best Track (black line). The dots are color coded with the vortex maximum 10-m wind speed (WS, kt).¶

MRW_GFSv16beta and MRW_GFSv15p2 generate left-of-track bias. Hurricane track from MRW_GFSv15p2 is closer to the Best Track compared with MRW_GFSv16beta.
MRW_GFSv16beta and MRW_GFSv15p2 do not capture the hurricane intensities (represented by max WS), especially before the landfall.

_images/tracker_timeseries_Michael_ufsv1.png

Time series of the vortex maximum surface wind speed (WS, left panel) and minimum mean sea level pressure (MSLP, right panel)¶

The maximum surface wind speed at the vortex center in MRW_GFSv15p2 (80 kts) is larger than MRW_GFSv16beta (60 kts). However, both two physics compsets do not reach the peak intensity identified in Best Track data (140 kts).
The minimum sea level pressures from MRW_GFSv15p2 and MRW_GFSv16beta are 965 hPa and 985 hPa, respectively, which are larger than Best Track data.

2.3. Summary and Discussion¶

The physics compset of GFS.v16beta in MRW.v1.0 does not show improvements compared with the compset of GFS.v15p2 in simulating Hurricane Michael track and intensity. The physics for MRW_GFS.v16beta was frozen in Jan 2020 for the public release of UFS MRW App version 1.0. Several major changes have been made to the GFS model after that, which include more vertical levels, several tuning parameters, and modified background diffusivity as a function of stability in the PBL scheme, etc. (Yang 2020). In GFS.v16.0.10 (GitHub tag created in Jun 2020), the simulated hurricane landfall location and hurricane intensity is closer to Best Track data compared to MRW_GFSv15p2.

References

Yang F. (2020). Development and evaluation of NCEP’s Global Forecast System Version 16. Unified Forecast System Community Webinar, Oct 22, 2020. [Link]