Extra-Tropical Storm Surge (ETSS 2.1) Pre-Implementation Briefing College Park, MD Oct 30, 2015 Arthur Taylor and Huiqing Liu Decision Support Branch

Sandy Supplemental Motivation Future coastal flood and storm surge warnings likely require overland guidance ETSS 1.5 (Oct 2014) and ESTOFS Predict storm surge to the coastline but not overland ETSS 2.0 (May 2015) Overland “surge only” guidance for East Coast and Gulf of Mexico Operationalize total water level post-processed guidance ETSS 2.1 (Nov 2015) Overland “surge and tide” guidance for East Coast and Gulf of Mexico AK Priority: Resolve Bering Strait problem via a single Bering Beaufort Chukchi basin Future – P-ETSS 1.0 (Jun 2016) Probabilistic Extra-Tropical overland Storm Surge and tide guidance Extra-Tropical Tropical Storm Surge to Coastline ETSS (1995 – 2014) ESTOFS (2012 – ) ETSS 1.5 (2014 – 2015) SPLASH (1972 – 1984) Overland Storm Surge ETSS 2.0 (May 2015) ------------------------------------- No Real-Time Ensemble No Climate Ensemble SLOSH (1984 – ) ------------------------------------- P-Surge 1.0 (2008 – 2013) MEOW/MOM (1986 – ) Overland Storm Surge + Gridded Tide ETSS 2.1 (Nov 2015) ------------------------------------- P-ETSS (2016 - ) No Climate Ensemble SLOSH + Tide (2012 – ) ------------------------------------- P-Surge 2.0 (2014 – 2015) P-Surge 2.5 (May 2015) No Climate Ensemble

ETSS 2.0 as of May 2015 Predicts overland inundation based on storm surge only Runs 4 times a day using 0.5 degree Global Forecast System winds and pressure to create 96 hours of hourly guidance Does so in the following areas … Arctic AK (updated Jan 1996), Bering Sea (updated Oct 1998), Gulf of AK (updated Apr 2008), East Coast (updated Feb 2009), Gulf of MX (updated Jan 2011), West Coast (updated Feb 2011) Based on the SLOSH model, but is intended for Extra-Tropical storms due to the wind forcing Does not account for Tides, Waves, or River Flow

ETSS 2.1 Objectives Overland Guidance from Extra-Tropical Surge and Tide 37 tidal constituents from ADCIRC’s EC-2014 (East Coast and Gulf of Mexico) 13 tidal constituents from Oregon State University's TPXO Global Tidal model (West Coast and Alaska) Provide 625 m resolution output (vs 2.5 km) BBC (Bering Beaufort Chukchi Seas) basin Update 20 year old bathymetry data and incorporate topography data Allow water to flow through the Bering Strait. Previously ETSS used two non-communicating basins on either side of the Strait. Bug fixes Merging Methods for East Coast and Gulf of Mexico Correct SHEF products to use MLLW (rather than MHHW)

Bug Fix – Merging Methods 2012-Sandy Adv 27 (Surge only) ETSS 2.0 (EX2 backup; smaller NY3 mask) Red=NY3; Purple=EX2; Black=2.5km CONUS ETSS 2.1 (EX2 ignored; larger NY3 mask) Red=NY3; Purple=EX2; Black=2.5km CONUS

Objective 1 Surge Only vs Surge + Tide (at 2.5 km) ETSS 2.1 Surge Only 2.5 km inundation for 2012-Sandy (Blue is field verified) ETSS 2.1 Surge + Tide 2.5 km inundation for 2012-Sandy (Blue is field verified)

Objective 1 Surge Only vs Surge + Tide (at 625 m) ETSS 2.1 Surge Only 625 m inundation for 2012-Sandy (Blue is field verified) ETSS 2.1 Surge + Tide 625 m inundation for 2012-Sandy (Blue is field verified)

Impact of Output Resolution on Inundation Extent ETSS 2.1 Surge + Tide 2.5 km inundation for 2012-Sandy (Blue is field verified) ETSS 2.1 Surge + Tide 625 m inundation for 2012-Sandy (Blue is field verified)

ETSS 2.1 Inundation Improvements ETSS 2.0 Surge Only 2.5 km inundation for 2012-Sandy (Blue is field verified) ETSS 2.1 Surge + Tide 625 m inundation for 2012-Sandy (Blue is field verified)

Room for Improvement Gridded vs Parametric and Native Res ETSS 2.1 Surge + Tide 625 m inundation for 2012-Sandy (Blue is field verified) SLOSH Surge + Tide native res. inundation for 2012-Sandy (Blue is field verified)

Objective 2: Opening the Bering Strait BBC (Bering, Beaufort, Chukchi Seas) ETSS 2.1 (Oct 2015) BBC (Green) replacing OTZ (Purple) NOM (Blue) Future Goal (beyond Jun 2016) Five (or more) nested higher resolution overland grids

Impact - Surge Only Forecast 0-h (06Z Oct 16) Surge values start out the same

Impact - Surge Only Forecast 12-h (18Z Oct 16) After 12 hours there are “minor” differences Bering Strait and North West Bering Sea

Impact - Surge Only Forecast 24-h (06Z Oct 17) After 24 hours there are “significant” differences Cause: ETSS 2.0 uses OTZ and NOM basins which have a common boundary (at the Bering Strait), but information is not shared

Impact - Surge Only Forecast 36-h (18Z Oct 17) After 36 hours the differences continue to spread Most of Bering Sea is impacted Very strong changes on “North Slope” Red Dog Dock key observation point

Impact - Surge Only Forecast 48-h (06Z Oct 18) After 48 hours the differences continue to spread

Statistical Analysis How to Determine Historic Events? Obs. at Nome (example), Prudhoe, and Red Dog Dock from 2006 to 2014 Human Impact: Observation above Ground (MHHW) > Child height (3 feet) 3 feet MHHW is 4.52 feet MLLW for Nome Surge Impact: Observation – Tide (aka Surge Only) > 4 feet

Storms Used to Validate the Model 15 for Human, 2 for Surge, 2 Omitted Storm ID Year Forecast Start Time 96 hour period (6 hour projection) over which RMSE, PAE is calculated 2006-A 2006 FEB 12 – 15 (00, 06, 12, 18z) FEB 12 01z – FEB 16 00z 2006-B OCT 15 – 18 (00, 06, 12, 18z) OCT 15 01z – OCT 19 00z 2007-A 2007 JAN 29 – FEB 1 (00, 06, 12, 18z) JAN 29 01z – FEB 2 00z 2007-B SEP 9 – 12 (00, 06, 12, 18z) SEP 9 01z – SEP 13 00z 2007-C NOV 28 – DEC 1 (00, 06, 12, 18z) NOV 28 01z – DEC 2 00z 2009-A 2009 MAR 4 – 7 (00, 06, 12, 18z) MAR 4 01z – MAR 8 00z 2009-B OCT 10 – 13 (00, 06, 12, 18z) OCT 10 01z – OCT 14 00z 2009-C DEC 5 – DEC 8 (00, 06, 12, 18z) DEC 5 01z – DEC 9 00z 2010-A 2010 APR 10 – 13 (00, 06, 12, 18z) APR 10 01z – APR 14 00z 2010-B AUG 14 – 17 (00, 06, 12, 18z) AUG 14 01z – AUG 18 00z 2011-A 2011 FEB 23 – 26 (00, 06, 12, 18z) FEB 23 01z – FEB 27 00z 2011-B NOV 8 (12, 18z) NOV 9 – 11 (00, 06, 12, 18z) NOV 12 (00, 06z) NOV 8 13z – NOV 12 12z 2011-C DEC 3 – DEC 6 (00, 06, 12, 18z) DEC 3 01z – DEC 7 00z 2012-A 2012 SEP 4 – 7 (00, 06, 12, 18z) SEP 4 01z – SEP 8 00z 2012-B OCT 4 (12, 18z) OCT 5 – 7 (00, 06, 12, 18z) OCT 8 (00, 06z) OCT 4 13z – OCT 8 12z 2013-A 2013 JUN 30 – JUL 3 (00, 06, 12, 18z) JUN 30 01z – JUL 4 00z 2013-B NOV13 – NOV16 (00, 06,12,18z) NOV 13 01z – NOV 17 00z 2014-A 2014 OCT 25 – 28 (00, 06, 12, 18z) OCT 25 01z – OCT 29 00z 2014-B NOV 9 – 12 (00, 06, 12, 18z) NOV 9 01z – OCT 13 00z

Mean RMSE and Peak Surge at 3 stations for 17 cases

Overall Model Skill ETSS 2.0 ETSS 2.1 ETSS 2.0 ETSS 2.1 PAE (feet) RMSE (feet) 2006A 2006 B 2007 A 2007 B 2007 C 2009 A 2009 B 2009 C 2010 A 2010 B 2011 A 2011 B 2011 C 2012 B 2013 B 2014 A 2014 B ETSS 2.0 0.91 0.81 0.96 0.86 0.78 0.89 0.77 1.27 0.74 1.82 1.01 0.84 1.28 1.20 1.04 0.94 ETSS 2.1 0.80 0.70 0.82 0.69 0.64 0.99 0.68 1.46 0.59 1.05 0.98 0.92 New wind Drag 0.62 0.57 0.75 0.46 0.66 0.56 0.79 0.67 0.49 1.11 0.87 PAE (feet) 2006A 2006 B 2007 A 2007 B 2007 C 2009 A 2009 B 2009 C 2010 A 2010 B 2011 A 2011 B 2011 C 2012 B 2013 B 2014 A 2014 B ETSS 2.0 1.31 1.42 0.97 0.64 1.52 1.11 1.37 1.34 0.53 3.08 1.92 0.78 1.72 1.56 1.44 1.21 ETSS 2.1 1.22 0.76 0.91 0.92 1.30 0.38 2.45 1.65 0.58 1.45 1.13 0.94 New wind Drag 0.45 0.72 0.79 0.41 0.52 0.69 0.80 0.31 1.28 0.95 0.18 1.33 0.82

ETSS 2.1 Should we Implement? Overland Guidance from Extra-Tropical Surge and Tide 625 m resolution East Coast and Gulf of Mexico 2.5 km resolution West Coast (and East Coast, Gulf of Mexico) 3.0 km resolution Alaska BBC (Bering Beaufort Chukchi Seas) basin Allows water to flow through the Bering Strait Avoids erroneous boundary influences Significantly improves the forecasts at the 3 observation sites for the 17 critical storms from 2006 to 2014 Bug fixes Merging Methods for East Coast and Gulf of Mexico Correct SHEF products to use MLLW (rather than MHHW)

Combined Impact of Sandy Supplemental Improvements ETSS 1.5 Surge Only 2.5 km to coast for 2012-Sandy (Blue is field verified) ETSS 2.1 Surge + Tide 625 m inundation for 2012-Sandy (Blue is field verified)

Backup

Surge Only Forecast 60-h (18Z Oct 18) After 60 hours the differences continue to spread

Surge Only Forecast 72-h (06Z Oct 19) After 72 hours the differences continue to spread

Surge Only Forecast 84-h (18Z Oct 19) After 84 hours the differences continue to spread

Surge Only Forecast 96-h (06Z Oct 20) After 96 hours the differences continue to spread

Tide Validation New Bering Sea (eBBC) # station RMSE (feet) 7 0.36

Tide Validation Gulf of Alaska (eGOA) # station RMSE (feet) 19 1.58

Tide Validation West Coast (eWC2) # station RMSE (feet) 34 0.92