1. Extra-Tropical Storm Surge (ETSS 1.5) Pre-Implementation Briefing College Park, MD October 8, 2014 Arthur Taylor, Huiqing Liu and Ryan Schuster MDL/NWS/NOAA

2. 2 Purpose Should we implement ETSS 1.5? GFS GRIB1 files are being deprecated –ETSS 1.0 uses these for input, so we need to change before or as part of the GFS upgrade Minimal resource impact –Same number of CPU for same amount of time –Slightly more memory required Additional benefits –Bug fixes for scripts and for the Alaska mask –Slightly improved accuracy and precision

3. 3 Background Extra-Tropical Storm Surge (ETSS) The ETSS model is a modification of the SLOSH model to use GFS winds to predict storm surge –Runs 4x daily –Predict surge to the coastline but not overland –Intended for large extra-tropical storms rather than hurricanes Output to NDFD CONUS grid with data from –The East Coast Basin (Updated: February 2009) –The Gulf of Mexico Basin (Updated: January 2011) –The West Coast Basin (Updated: February 2011) Output to NDFD Alaska grid with data from –The Arctic Ocean Basin (Updated: January 1996) –The Bering Sea Basin (Updated: October 1998) –The Gulf of Alaska Basin (Updated: April 2008)

4. 4 ETSS 1.5 Enhancements Technical Objectives Convert from GFS GRIB1 to GRIB2 Move to vertical structure Bug fixes for error handling Science Objectives  Correct mask for south Bering Sea just north of Aleutian Islands to use Bering Sea vs. Gulf of Alaska guidance  Switch input from 1 degree to 0.5 degree winds and pressure  Switch output from 5 km NDFD CONUS; 6 km NDFD Alaska to 2.5 km NDFD CONUS; 3.0 km NDFD Alaska

5. 5 ETSS 1.5 Mask Correction Issue: Pink area on the NDFD Alaska grid came from Gulf of Alaska basin instead of Bering Sea basin Alaska Region and WFO’s requested it come from the Bering Sea basin

6. 6 ETSS 1.5 Mask Correction Issue: Red circled area on the NDFD Alaska grid came from Gulf of Alaska basin Alaska Region and WFO’s requested it come from the Bering Sea basin http://nws.weather.gov/mdlsurge/comparison/

7. 7 ETSS 1.5 OPC Science Review Conclusions 1.ETSS 1.5 showed as good and at times finer detailed storm surge guidance than ETSS 1.0 2.ETSS 1.5 compared well with NOS water level guidance 3.ETSS is the only guidance available for the Bering Sea and Arctic

8. 8 ETSS 1.5 NHC Science Review Conclusions 1.Changes to the ETSS output were negligible 2.Differences between ETSS 1.5 and observations were generally within a half foot (0.2 meters) 3.Largest variance between observations and ETSS was consistently seen at the Prudhoe Bay site (MDL – ETSS 2.1 may address) 4.When differences between the observations and ETSS were noted, the difference seen most frequently was WL too high at low tide 5.There were cases where both versions of ETSS were too slow to return WL to normal after surge events

9. 9 MDL Comparison ETSS 1.5 vs 1.0 Extra-Tropical March 2013 Extra-Tropical February 2014 # StationsRMSE (ETSS 1.0)RMSE (ETSS 1.5) NY, NJ70.64 feet0.63 feet NJ, DE (bay)50.63 feet0.62 feet MD, Chesapeake70.63 feet0.59 feet Outer Bank NC30.65 feet0.63 feet Overall220.64 feet0.62 feet # StationsRMSE (ETSS 1.0)RMSE (ETSS 1.5) NY, NJ70.59 feet0.58 feet NJ, DE (bay)50.66 feet0.64 feet MD, Chesapeake70.61 feet0.58 feet Outer Bank NC30.69 feet Overall220.63 feet0.61 feet

10. 10 MDL Comparison ETSS 1.5 vs ETSS 1.0 Hurricane Irene 2011 # StationsRMSE (ETSS 1.0)RMSE (ETSS 1.5) NY, NJ70.72 feet0.74 feet NJ, DE (bay)50.70 feet0.76 feet MD, Chesapeake120.47 feet0.49 feet Outer Bank NC30.49 feet0.58 feet Overall270.58 feet0.61 feet Peak surge comparison: NY, NJ – Evenly split NJ, DE (bay) – ETSS 1.5 is better than ETSS 1.0 MD, Chesapeake – ETSS 1.5 is better than ETSS 1.0 Outer Bank NC – ETSS 1.5 is better than ETSS 1.0

11. 11 ETSS 1.5 Enhancements Science Objectives Correct mask for south Bering Sea just north of Aleutian Islands to use Bering Sea vs. Gulf of Alaska guidance  Switch input from 1 degree to 0.5 degree winds and pressure  Overall impact is negligible  Higher fidelity to the wind model is for the most part beneficial  More impactful up bays and estuaries where direction and magnitude are critical Switch output from 5 km NDFD CONUS; 6 km NDFD Alaska to 2.5 km NDFD CONUS; 3.0 km NDFD Alaska  ETSS 1.5 showed as good and at times finer detailed storm surge guidance than ETSS 1.0

12. 12 Implement ETSS 1.5  OPC – Recommends implementation  NHC – Recommends implementation  MDL – Recommends implementation  NCO?  Others – Alaska Region?  Others – WFOs?

13. 13 Future FY15Q3 – ETSS 2.0 “Overland East Coast, Gulf of Mexico + Post Processing” –Add gridded tidal forcing where available –Re-enable overland calculations –Nest coarse Extra-Tropical basins with finer Tropical basins to produce overland guidance –SHEF encode the station based Total Water Level guidance available on MDL’s website for eventual use in AHPS FY15Q4 – ETSS 2.1 “Bering Sea and Arctic” –Add gridded tidal forcing –Replace Bering Sea and Arctic basins from 1990’s with a single uniform grid with overland information to resolve Bering Strait

14. 14 Questions

15. 15 ETSS-1.5 Mask Correction Unalaska station NHC – New version (right) too low with high and low tides MDL – Station plots are derived from text as opposed to gridded product, so are not impacted by mask correction MDL – Difference here is based solely on 1 degree vs 0.5 degree wind input ETSS ETSS 1.5

16. 16 Sample Stations ET-March 2013

17. 17 Sample Stations ET-February 2014

18. 18 Sample Stations Hurricane Irene 2011