1. Overview and outlook of NCEP's operational wave models
NOAA WAVEWATCH III
Overview and outlook of NCEP's
operational wave models
J. Henrique Alves & Hendrik L. Tolman
SAIC-GSO at NOAA/NWS/NCEP
Marine Modeling and Analysis Branch, EMC

2. Outline Short story of wind waves
From birth to breaking, what are they?
Representing the sea-state: significant wave and the wave spectrum
Forecasting waves using numerical models
The NCEP ocean wave guidance
Performance evaluations
Recent Changes and Future directions
Maximum wave in hurricane advisories
Tutorial: NCEP operational wave products
What are they?
Grib & grab guide

3. Wind Waves What are they?
Always born windseas, sometimes die as swells
How are they generated?
Wind turbulence: resonance
Pressure differences, disturbed field
Many scales are excited
From a cm to a whole km in length
As fast as a crawl, near 100mph
From a mm to 10 stories high
Multiple directions
If you’re out at sea, can’t ignore them
L = 1.56 T2
C = L / T
C = 1.56 T

4. Wind Waves Important parameters describing one wave
Water movements associated with wind waves
Need to be described, and predicted. But how?
How many parameters to describe sea state?
1ary: Height – Length – Period – Direction
2ary: Speed - Steepness
Many waves at same time: impossible to have a set of descriptive parameters for each wave individually
Solution: describe sea-state with average measures for wave fields: representative wave, wave spectrum

5. Wind Waves 1st approach: single representative wave (1940’s)
Most popular: Significant wave height Hs
Average height of the highest 33% of all waves.
Hs is closely what we see <= smaller waves are dwarfed against the background of larger ones
Theory, empirical data: heights follow a Rayleigh distribution. For Hs = 10m (33ft), one can expect:
1 in 10 waves to be larger than 10.7m (36ft)
1 in 100 waves to be larger than 15.1m (51ft)
1 in 1000 waves to be larger than 18.6m (62ft).
Largest individual wave may be roughly 2 x Hs
Associated parameters: Tp, Tz, p, m
Rayleigh breaks down in growing and mixed seas
In mixed seas, single wave parameter means little

6. Wave Spectrum Goal: represent main properties of multiple wave systems
What defines fully a wave?
L or T (dispersion relation)
Direction
Height (wave energy)
Wave spectrum bundles such information for multiple wave systems
Displays distribution of wave energy in “classes” of direction and frequency (period)
Easily represented graphically (sample spectrum at buoy 51004)

7. Wave Spectrum WAVEWATCH III Output spectra Blue: nearly no energy
Pink: maximum energy
Each contour has twice the energy of the previous
Directions show where wave is going to
Frequency range:
Center: f=0.04Hz (T=25s)
Outer: f=0.25Hz (T=4s)
Resolution:
24 directions
25 frequencies
600 “waves” (components)

8. Wave Spectrum Wave model spectral data
Red box: wave field traveling toward SE, with Tp~10s. Energy concentrated in f and  : regular, organized wave field
Blue box: wave field travels toward SW at lower periods. But more chaotic as energy spreads over wider range in  at higher f
Main fields: information in wave spectrum can be summarized
Hs = 0.7m, Tp = 6.6s
Hs = 1.4m, Tp = 15.9s
Hs = 1.4m, Tp = 7.0s
Hs = 0.3m, Tp = 9.9s
Sea state on 06/26/2000
Buoy 51004
Single wave scenario
Hs = 2.2m
Tp = 15.9s
Tm = 10s
p = 16o
m = 180o
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9. Wave Field Bulletin
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Such summary, in tabular format, is the basis of bulletins provided in our web site and in AWIPS
To a forecaster, spectrum provides qualitative information
Bulletins give quantitative info on up to six largest wave fields at a given time in the fcst horizon

10. Wave Field Bulletin AWIPS : feet, dir. from
Sample bulletin
1st column: date and hour
2nd column: overall Hs and number of identified individual wave fields
Next six columns (only two shown): height, period and direction of individual wave fields

11. NOAA WAVEWATCH III (NWW3) Model
bathymetry & coast line
Full spectral wave field FCST
10m winds, SST, Tair, [ice]
WAVEWATCH III MODEL
Wave Propagation
great circle
refraction
dispersion
Model Physics
growth (wind input)
decay (whitecapping)
wave-wave interaction
Reduced Output
local spectra
mean/integral field parameters

12. Operational NWW3 Model Suite (NCEP Guidance)
NOAA WAVEWATCH III: Version 1.18 replaced all previous operational models at NCEP, March 2000.
NWW3: Global, 1.25x1o, 168h, 3-hourly GFS winds
WNA: W North Atlantic, 0.25x0.25o, 168h, 3h GFS winds
NAH: Hurricane version of WNA, 0.25x0.25o, 72h, 1h GFS+GFDL winds
ENP: E North Pacific, 0.25x0.25o, 168h, 3h GFS winds
NPH: Hurricane version of ENP, 0.25x0.25o, 72h, 1h GFS+GFDL winds
AKW: Alaskan Waters, 0.5x0.25o, 168h, 3h GFS winds
All models: 24 directions, 25 frequencies, 4 daily cycles (00z, 06z, 12z, 18z) with 6h hindcasts for continuity
NOAA WAVEWATCH III: Version 2.22: operational since Aug. 2002
180h
March 2004
180h
GFDL
180h
180h

13. NCEP Guidance: The Global Model Domain
March 2000

14. NCEP Guidance: The WNA Model Domain
Operational WNA Model Domain implemented since March 2000
Also serving NAH Model since July 2001
Previous ECG WAM Model Domain (Operational at NCEP till March 2000, red square)

15. NCEP Guidance: The ENP and AKW Model Domains
ENP Model Domain implemented June 2002
Also serving NPH Model since Aug 2003
AKW Model Domain implemented on March 2000

16. NCEP Guidance: General Quality Evaluation
Validation statistics per month/season vs. buoy or satellite data.
Since February 1997 for Global model.
Since August 2000 for Regional models.
Six-month comparison with old operational global wave model (WAM). Strong points:
Good overall performance (rms errors ~10- 20% of mean measured Hs).
Improved max and min storm Hs relative to previous global model (WAM).
Comprehensive coverage of areas of interest by regional models

17. NCEP Guidance: General Quality Evaluation (Winds)
Weak points of external forcing affecting wave models:
Wave models, only be as good as its driving forces.
For our models (deep water): Wind!
Most important problems, GFS and GFDL resolutions:
Temporal output resolution, of GFS GFDL is much coarser than internal model time step:
Interpolation smears small systems with strong winds => underestimation of extremes.
Solutions: shorter output step for surface fields
Spatial resolution in GFS and GFDL, constrained by economical considerations (more difficult):
Problems with prediction of small-scale systems (frontal system moving offshore GMex and EC).
Poor land-sea (boundary layer) transition: problem for wave growth within systems moving offshore.

18. NCEP Guidance: General Quality Evaluation (Winds)
Weak points of the present wave models.
Resolution:
Spectral resolution is “borderline” enough, lacking for swell dispersion
Spatial resolution could locally be better for islands (partially solved) and hurricanes when GFDL winds are available
Shelf bathymetry not well resolved nearshore: problem for propagation of waves generated offshore
Physics (secondary, fine tuning):
Slow initial growth, but good predictions of peak and waning stages of storm.
Errors in spectral shape near peak make swell front arrival gradual and slightly late (DIA + numerical).

19. NCEP Guidance: Why Have Special Hurricane Models?
Why do we need a special Hurricane version (NAH, NPH) of regional models (WNA, ENP).
Wave model can only be as good as the winds that drive it.
Hurricane winds are not done particularly well by the GFS due to resolution problems and due to limitations of the model physics.
Better results expected when higher resolution models are used such as the GFDL model.
Need for blended GFS/GFDL winds.

20. NCEP Guidance: Why Have Special Hurricane Models?
AVN
AVN+GDFL
What got us started: Floyd and Gert Sept. 1999

21. NCEP Guidance: Why Have Special Hurricane Models?
Debby peak wave period (s)
2000/08/23 12z ( + 36 h)
AVN winds
AVN + GFDL winds

22. NCEP Guidance: Why Have Special Hurricane Models?
AVN winds
AVN + GFDL winds

23. NCEP Guidance: NAH vs. WNA during Lili and Isidore (2002)

24. NCEP Guidance: NAH vs. WNA during Hurricane Isabel (2003)
Isabel’s track and locations with buoy observations

25. NCEP Guidance: NAH vs. WNA during Hurricane Isabel (2003)
9/13/2003:
Isabel is small and poorly resolved by GFS
9/17/2003:
Isabel is larger and well resolved by GFS
WNA and NAH hindcasts of Isabel collocated with Jason-1 data.

26. NCEP Guidance: NAH vs. WNA during Hurricane Isabel (2003)
Hindcast at buoys near track
Maximum wave heights very well represented.
Initial swell arrivals underestimated. Swells generated when Isabel was cat. 5 hurricane (wind errors).
Do we believe last observation of Buoy in surf zone !

27. NCEP Guidance: NAH vs. WNA during Hurricane Isabel (2003)
For buoys at the Atlantic seaboard in shallow water, swells are overdone, most likely because shallow water processes are not well resolved yet.
Some tidal influence to be seen in data (not in model yet).
Hindcast at buoys south of track

28. NCEP Guidance: NAH vs. WNA during Hurricane Isabel (2003)
Many features as in previous time series.
Swells from NAH systematically higher.
Highest wave heights from WNA larger due to weaker winds over larger areas
Last two points also clear in previous slides.
Hindcast at buoys north of track

29. NCEP Guidance: NAH vs. WNA during Hurricane Isabel (2003)
WNA misses Isabel, swells
WNA and NAH similar

30. NCEP Guidance: NAH vs. WNA during Hurricane Isabel (2003)
This is an hourly animation of Isabel wave heights from hindcasts.
Note the pulsating nature of the wave height fields, which has to do with the hourly wind fields.
Possible reasons
Nature
GFDL peculiarities
Garden Sprinkler Effect for swells.

31. NCEP Guidance: NAH vs. WNA during Hurricane Isabel (2003)
NAH forecast envelope
Buoy 95% confidence interval
Ranges of wave heights in 72h forecasts

32. NCEP Guidance: NAH vs. WNA during Hurricane Isabel (2003)
12 h forecast
Max Hs > 45 ft
nowcast
Max Hs > 50 ft
24 h forecast
Max Hs > 55 ft
48 h forecast
Max Hs > 50 ft
Forecast wave heights very consistent and verify well against buoy and altimeter data
Timing is the biggest issue in the forecast, with NAH (GFDL) being a little fast.
WNA (GFS) with similar patterns, being a little slow in bringing Isabel to the shore.
NAH, 18/9/ :00 UTC

33. Maximum Hurricane Wave Height: Parametric Model for Advisory
Parametric model of Young (1988) [modified by Wu] basis of estimation of maximum Hs for TPC advisory
Relates maximum Hs and an equivalent fetch
Basis of Young’s approach:
2G wave model data using idealized hurricane winds
Relates max(Hs) and equivalent fetch (XEQ) using JONSWAP parametric formula
XEQ is assumed a function of Vf and Umax
O(2) polynomial in Vf & Umax is fit to JONSWAP formula, given model maximum Hs, providing XEQ
Given Vf, Umax and Rmax (nonlinear scaling factor), model estimates maximum Hs
EMC: Testing sensitivity to tuning data (wave model Hs) and to assumptions behind XEQ

34. Maximum Hurricane Wave Height: Sensitivity of Parametric Model
Effect of changing model only
Same parameterization of XEQ
New tests: WAVEWATCH III
Over 100 model runs, several Vf, Umax and Rmax
New XEQ, f(Rmax), adjusted by Vf, scaled by Umax
Scatter reduced O(100)
Highly sensitive to base wave model
New form of XEQ: higher accuracy (model independent?)
WAVEWATCH III, widely tested in real cases: better?

35. Recent upgrades
The following changes and of the model suite were made in the past two years:
Upgrade of blending scheme for NAH winds and upgrade time resolution of NAH wind fields to 1 hour (start of 2002 Hurricane season).
Second release of WAVEWATCH III code (Islands)...
Four cycles, eight-day forecast for all non-hurricane models.
North Pacific Hurricane (NPH) wave model.
Continuous upgrades to output points. New buoys and new requests added. West coast temporary output points removed from global model.

36. Recent upgrades: Hourly Winds in Hurricane Models
Michelle at 11/04/ z
wind speeds
wave heights
every 6 hours
every 1 hour
every 6 hours
every 1 hour
Two eyes of hurricane at the off hour due to rapid movement of Michelle, no consistency in wave fields.
Michelle with single eye at off hour, much more consistent and higher waves.

37. Recent upgrades: Island Blocking
bias without obstructions
bias with obstructions
Unresolved islands have been included in version 2.22 of WAVEWATCH III as obstructions in the grid. Even in the high resolution (25 km) WNA model this can have a major impact on local biases, as is shown here with model biases against the ERS-2 altimeter for the year 2001.

38. Recent upgrades: Data Assimilation
Data assimilation is not essential in wave modeling, due to the forced and damped nature of the problem.
There is grossly insufficient data for making a data- dominated analysis
Benefit in using data in hindcast and short term fcst shown at NCEP (WAM), as well as in other centers.
Objective: assimilate wave data into global wave model:
Buoy data from fixed platforms.
Altimeter wave data from ERS2 satellite.
Data expected in the near future: GFO and Jason-1
Observations assimilated using variational method as in, for instance, SST analysis.
Observations provide Hs, model works with E(f,).
Model spectra adjusted for corrections in Hs by rescaling.
Operational, Mar 2, 2004

39. Recent upgrades: Data Assimilation

40. Recent upgrades: Data Assimilation
Data assimilation of buoy and ERS2 data: systematically positive impact on the quality of the hindcasts and the short term wave forecast in the global NWW3 wave model.
Implementing this data assimilation scheme will put us in an excellent position to rapidly test and add other altimeter wave data source, with expected additional incremental improvement to hindcast & short term forecast

41. The future
The next step in expanding the functionality of WAVEWATCH III is to generate a multi-scale version of this model :
Regional models have a spatial resolution of 25km. In the next decade, we expect to be able to increase the near-coast resolution to 5-10km, using multi-scale technology
Two-way nesting of models with different scales that run simultaneously.
Moving nests follow features of interest, particularly hurricanes.
Hurricane nests plus coastal nests remove the need for running separate large regional models.
Selective application of highest resolution nests makes ensemble wave forecasting more feasible.
coupling with WRF

42. The Future Deep ocean model resolution dictated by GFS model
Higher coastal model resolution dictated by model economy
Highest model resolution in areas of special intest
Hurricane nests moving with storm(s) like GFDL and WRF

43. The future
At the moment we are not looking at adding regional models, or at increasing the spatial resolution of the existing model. Instead, the focus will be on new products:
Adding one or more steepness measures to the model output
Safety issue for (small) ships
Input from field appreciated (NCEP/OMB)
Doing separation of individual wave systems for all grid points, not just for output points.
Identify each individual swell field in space and time. Ideal for IFPS
Collabotation with Jeff Hanson (JHU).
Looking for funding
Bulletins in spreadsheets (Jeff Lorens, WR)
(USACE)

44. The future
Further efforts have been focused on physics of the model, to improve general behavior:
Improved nonlinear interactions for more realistic directional spreading in wind seas, and crisper swell arrival.
Improve particularly dissipation to prepare for later coupling with ocean models.
Improve stress calculations and hence growth rates for extreme (hurricane) conditions. Collaboration with Univ. of Rhode Island and Univ. of Miami.
These are all long term (multi-year) projects.

45. Products Mean wave parameters in GRIB format
Overall significant wave height.
Mean direction and period.
Peak direction and period.
Wind sea direction and period.
NOT AVAILABLE : mean swell height and direction (see next slides).
Text bulletins with different wave systems for output locations

46. Products There is rarely just one swell field.
What is the meaning of "the" swell height and the mean swell period and direction?
Up to nine swell fields can be identified in the spectral plots on the right!

47. significant wave height (m)
Products
significant wave height (m)
Wind seas
Swell ?

48. mean wave period (s) and direction
Products
mean wave period (s) and direction
Wind seas ?
Swell !
Swell ?

49. peak wave period (s) and direction
Products
peak wave period (s) and direction
Swell !
Swell !

50. wind sea wave period (s) and direction
Products
wind sea wave period (s) and direction
Wind seas
Wind sea !

51. wind speed (kn) and direction
Products
wind speed (kn) and direction

52. Products Numerical data and time evolution from bulletin (buoy 51004)
H = 0.6m T = 12s
Swell H = 1.2m T = 17s
marginal wind sea + swell T = 8s
marginal wind sea H = 1.6m T = 8s
Swell H = 0.9m T = 15s
Swell H = 0.3m T = 15s
different!
Swell H = 1.5m T = 11s

53. Products Available on AWIPS :
Most model fields. Errors in AWIPS graphics near coast. It takes some time to catch up with added cycles and extended forecast ranges.
Text bulletins in version modified for the use of WFOs (wave heights in feet, meteorological convention for directions).
Not available on AWIPS :
Spectral plots as used in this presentation. There are no plans for including these in in AWIPS. See also future plans slides below.

54. Products Available on web site:.
ALL model data, usually within 1 hour of the model run.
Historical hindcast data.
Validation data.
Background information, including a primer and presentations like this one.
We will work with any WFO or region to get products out as needed.
New output points (2-3 week turn around time).
Suggestions for new products welcome.
NAWIPS … (OPC, Hawaii …)

55. Finally ....
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