993
NOUS41 KWBC 241630
PNSWSH

Service Change Notice 25-48
National Weather Service Headquarters Silver Spring MD
1230 PM EDT Tue June 24 2025

To: Subscribers:
 -NOAA Weather Wire Service
 -Emergency Managers Weather Information Network
 -NOAAPort
 Other NWS Partners, Users and Employees

From: David Michaud, Director
 NCEP Central Operations

Subject: Upgrade to Hurricane Analysis and Forecast System
(HAFS)to version 2.1: Effective July 24, 2025

Effective on or about Thursday, July 24, 2025 with the 1200
Coordinated Universal Time (UTC) cycle, the National Centers for
Environmental Prediction (NCEP) Central Operations (NCO) will be
implementing a new upgrade of Hurricane Analysis and Forecast
System version 2.1 (HAFSv2.1) for both HFSA and HFSB
configurations.  In the event that the implementation date is
declared a Critical Weather Day (CWD), an Enhanced Caution Event
(ECE), or other significant weather is occurring or is
anticipated to occur, implementation of this change will take
place at 1200 UTC on the next weekday not declared a CWD and
when no significant weather is occurring.

The scientific and technical enhancements include the following:
- Model code updates based on later UFS revision (July 3, 2024)

Atmospheric physics advances:
* Improved Scale-Aware Simplified Arakawa-Schubert (sa-SAS)
convection scheme using:
* scale-adaptive convective cloud water calculations
* prognostic sigma closure for all TC basins
* Improved Turbulent Kinetic Energy (TKE)-based Eddy-Diffusivity
Mass-Flux (EDMF) Planetary Boundary Layer (PBL) scheme
* Enabled exponential-random cloud overlap method in the Rapid
Radiative Transfer Model for GCMs (RRTM-G)

Ocean model updates:
* Initialized ocean model using the latest RTOFS version 2.5,
which is scheduled to be implemented into operations along with
HAFS version 2.1
* Upgraded ocean coupling and improved ocean model mixed layer
scheme

Vortex Initialization (VI) and Data Assimilation (DA)
improvements:
* Improved VI for more accurate storm intensity representation
* Applied wavenumber filtering to DA increments
* Enabled storm-following Three-Dimensional Incremental Analysis
Update (3DIAU) in inner-core DA
* Assimilated NOAA-21 Advanced Technology Microwave Sounder
(ATMS) and Cross-Track Infrared Sounder (CrIS) observations
* Turned off assimilation of both P3 and C-130 Stepped Frequency
Microwave Radiometer (SFMR) surface wind speed observations

The HASFv2.1.0 system has been fully tested and compared with
the forecast skill of 2024 operational HAFSv2.0, demonstrating
overall improved tropical cyclone track and intensity forecast
guidance in all global oceanic basins.

Product Timing Changes:
There will be no changes on the HAFS product delivery time for
users of public data on the NOAA Operational Model Archive and
Distribution Service (NOMADS).

Data files for the HAFS remain at their current location on
NOMADS/FTPPRD web services at:
ftp://ftp.ncep.noaa.gov/data/nccf/com/hafs/prod
https://nomads.ncep.noaa.gov/pub/data/nccf/com/hafs/prod

An event driven parallel feed of HAFSv2.1.0 data is available on
the NCEP sites at the following URLs:
ftp://ftp.ncep.noaa.gov/data/nccf/com/hafs/para
https://nomads.ncep.noaa.gov/pub/data/nccf/com/hafs/para

Sample HAFS products from HAFSv2.1 are available at:
https://www.emc.ncep.noaa.gov/gc_wmb/vxt/zack/HAFS_Sample_Files/
HFSA_sample/hafs/v2.1/
https://www.emc.ncep.noaa.gov/gc_wmb/vxt/zack/HAFS_Sample_Files/
HFSB_sample/hafs/v2.1/

NCEP encourages users to ensure their decoders are flexible and
are able to adequately handle changes in content order, changes
in the scaling factor component within the product definition
section (PDS) of the Gridded Binary (GRIB) files, and any volume
changes which may be forthcoming. These elements may change with
future NCEP model  implementations. NCEP will make every attempt
to alert users to these changes prior to any implementations.
Any questions, comments or requests regarding this
implementation should be directed to the contacts below.

For questions regarding these model changes, please contact:

Dr. Zhan Zhang
Hurricane Modeling Project Lead
NOAA/NCEP/Environmental Modeling Center
National Centers for Weather and Climate Prediction
College Park, MD
301-683-3674
zhan.zhang@noaa.gov

For questions regarding the data flow aspects of these datasets,
contact:
Margaret Curtis - HPC Dataflow Team Lead
NCEP Central Operations HPC Dataflow Team Lead
ncep.pmb.dataflow@noaa.gov

National Service Change Notices are online at:

https://www.weather.gov/notification