ADDRESSING THE NEARSHORE WAVE FORECASTING
DILEMMA: OBSERVATIONS FROM RECENT MODIFICATIONS
TO THE GLERL WAVE MODEL
18th Annual Canada/US
Great Lakes Operational Meteorology Workshop (GLOMW)
Toronto, Canada
March 24 2010
Cory Behnke Meteorologist
NOAA/NWS Detroit-Pontiac
Abstract
2
Despite more reliable wave height forecasts, the sparsity of real-time marine observations
fosters an uncertainty, particularly within the nearshore environment. Recent feedback from
the marine community in southeastern Michigan and Saginaw Bay suggests further
improvements in wave height forecasts are needed. Given the motivation, limitations of the
baseline Great Lakes Environmental Laboratory wave model were addressed for much of
2009 by including a shallow water consideration and an increased grid resolution to 2.5 km.
A basic sensitivity examination between the multiple setups was conducted using steady state
comparisons and results will be provided. With anecdotal accounts remaining the sole means
of "ground truth", maintenance trips into the central waters of Saginaw Bay on 9-19-2008
and 7-27-2009 provided for a great opportunity in qualitatively assessing forecast
performance.
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
3/24/2010
Motivation
3




Recent feedback out of Saginaw Bay and Lake St Clair is that wave height
forecasts need further improvement.
Areal coverage of the Great Lakes system is approximately 95,000 sq
miles/246,000 sq km.
Roughly 9,900 miles/15,900 km of shoreline.
20 total buoys. 9 U.S. 11 Canada. All located outside of 5nm from shoreline.
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
3/24/2010
Outline
4

Modifications to Operational GLERL Wave Model
•
Shallow Water Considerations1
•
Increased Grid Resolution to 2.5 km2

09/19/2008 Saginaw Light #1

07/27/2009 Gravelly Shoal
1) Implemented October, 2008 – Greg Mann
2) Implemented July, 2009
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
3/24/2010
Available Wave Forecast Guidance
5
Great Lakes Environmental Lab (GLERL)
Wave Model
•
•
•
•
Inputs include: NDFD 10m winds, NDFD 2m air
temperatures, GLERL LSTs and GLERL Ice
Analysis.
Run on-demand for specific domain within
WFO (~5-10 min)
Horizontal resolution is same as the host GFE
grids. NDFD currently supports 5km.
WaveWatch III
•
•
•
•
Inputs include: NDFD 10m winds, NDFD 2m air
temperatures, MMAB SSTs and Ice Analysis.
Runs for the Great Lakes occur 4 times daily at
NCEP (~40 min)
Horizontal resolution is roughly 4 km (latitudelongitude grid)
Runs to 156 hrs.
Runs to 156 hrs
A main limitation of the baseline
GLERL model is that shallow water
effects are ignored.
Source terms include: bottom friction,
depth-induced breaking, and
scattering due to wave-bottom
interactions.
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
3/24/2010
Wave Model Modifications
6

Shallow water physics approximation




Strictly Bottom Effects - does not include direct reflection or refraction effects
(although refraction may result from bottom drag effects on wave phase vector).
Phase speed of wave is incrementally lowered when Wavelength >= Depth and
limited by the breaking steepness.
Adjustment is a proportional comparison between the depth limited wavelength
and deep water wavelength acting on the deep water phase speed.
When wavelengths are shortened to breaking steepness (amplitude * 7 ~=
wavelength) or the wave height exceeds 40% of the depth the phase is relaxed
to a value greater than the deep phase effectively removing the stress and
allowing amplitude dampening – mimicking breaking.
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
3/24/2010
Steady State Flow Simulations
7

A total of 3600 simulations were run to steady state for
the western Great Lakes.

Horizontal resolution: 2.5 km and 5 km.

Shallow, Deep (baseline) water physics.



15 wind directions. [040, 090, 130, 180, 210, 220, 230,
240, 250, 260, 270, 280, 290, 320, 360]
12 wind speeds. [6, 10, 14, 18, 22, 26, 30, 34, 38, 42,
46, 50 knots]
5 stability classes. [stable, marginally stable, neutral,
marginally unstable, unstable]
A random sample was gathered to understand the
changes to the model output brought on by the
introduction of the shallow water physics and
increased resolution. Total sample size was 500
conditions.
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
3/24/2010
Comparison Results
8
On average, the shallow water adjustment increases gridded wave heights.
•
•
•
5.0 km Deep to 5.0 km Shallow results in an average increase of around 7.8%
2.5 km Deep to 2.5 km Shallow results in an average increase of around 5.0%
5.0 km Deep to 2.5 km Shallow results in an average increase of around 3.4%
Shallow water adjustment has the greatest impact on nearshore grids and under moderate to
strong flows.
•
•
Nearshore environment: average increase of around 10.4% for 5km Deep to 5km Shallow.
average increase of around 6.5% for 2.5km Deep to 2.5km Shallow.
average increase of around 4.8% for 5km Deep to 2.5km Shallow.
>=18 knots: average increase of around 10% for 5km Deep to 5km Shallow.
average increase of around 7.1% for 2.5km Deep to 2.5km Shallow.
average increase of around 6.2% for 5km Deep to 2.5km Shallow.
Deep 270 22kt 2.5km
Shallow 270 22kt 2.5km
Deep 270 22kt 5km
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
Shallow 270 22kt 5km
3/24/2010
Comparison Results cont…
9
Shallow water adjustment also outputs greater wave heights on average for the deeper
open lake environment.

5.0 km Deep to 5.0 km Shallow results in an average increase of around 4.0%

2.5 km Deep to 2.5 km Shallow results in an average increase of around 2.9%
Nov 13, 2003
Northern Lake Huron ~19 ft
Deep 320 42kt 2.5km
Shallow 320 42kt 2.5km
2003
2003
2003
2003
2003
11
11
11
11
11
13
13
13
13
13
9 21.9 26.7 291 4.24
10 20.7 26.3 297 5.38
11 21.3 27.3 302 5.32
12 21.0 26.5 312 5.77
13 21.1 27.4 308 5.78
Southern Lake Huron ~24 ft
Deep 290 42kt 2.5km
Shallow 290 42kt 2.5km
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
2003
2003
2003
2003
2003
11
11
11
11
11
13
13
13
13
13
8 21.1 26.1 283 3.78
9 21.3 26.7 281 5.44
10 22.8 29.3 286 6.01
11 21.7 27.0 290 5.91
12 21.7 27.2 292 7.17
3/24/2010
Comparison Results cont…
10
Solely increasing resolution results in a reduction of forecasted wave heights. This
difference is attributed to coarse grid averaging.


Shallow 220 22kt 5km
The 5km to 2.5km disparity is most pronounced in nearshore regions where bathymetrical
gradients are greatest .
In general, increased resolution leads to negligible differences for the open lake or where fetch
remains relatively constant.
Shallow 220 22kt 2.5km
Deep 220 22kt 5km
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
Deep 220 22kt 2.5km
3/24/2010
Effects of Shallow Water Approximations
11



Greater wave heights in the shallows (subject to breaking - so the height is depth
limited
Introduction of wave height variation in shallow water associated with bottom
structure (e.g. shoals, island slopes)
Higher wind conditions result in increased wave heights in deep water from wave
trains that originate in extensive shallow regions (e.g., wave generated in Saginaw
Bay translating to Lake Huron)
•
•
Initial waves are steeper producing shorter period wave trains for the given
amplitude allowing for greater wind stress.
Furthermore, slower dispersion of the wave phase in the deep water results in
prolonged surface stress resulting in maintenance greater amplitude.
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
3/24/2010
12
Short Case Studies
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
3/24/2010
WRF Configuration
13
•
•
•
•
•
•
•
•
2.5 km delta-x
40 levels
No convective scheme
Goddard Microphysics
Mellor-Yamada-Janjic PBL with Eta Similarity Scheme
NOAH land surface model
NAM initial and boundary conditions
(Replicate real-time forecast setup)
High Resolution RTG SST
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
3/24/2010
19 September 2008
14



NWS DTX electronics staff left Essexville CG aboard vessel at approximately 14Z.
Approximate 1 hr journeys to and from Saginaw Bay Light #1, SBLM4
Waves of 4 feet prevented personnel from landing at site!
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
3/24/2010
19 September 2008 - Nearshore Forecast
15
Inner Saginaw Bay
322 PM EDT THU SEP 18 2008
.FRIDAY...SOUTH WINDS 5 TO 10 KNOTS...INCREASING TO 10 TO 15 KNOTS.
MOSTLY SUNNY. WAVES 1 TO 2 FEET.
1000 PM EDT THU SEP 18 2008
.FRIDAY...SOUTH WINDS 5 TO 10 KNOTS...INCREASING TO 10 TO 15 KNOTS.
MOSTLY SUNNY. WAVES 1 TO 3 FEET.
353 AM EDT FRI SEP 19 2008
.TODAY...SOUTHEAST WINDS 10 TO 15 KNOTS...TURNING TO SOUTH. PARTLY
SUNNY. WAVES 1 TO 2 FEET.
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
3/24/2010
GSLM4 2008 09 19 07 13 130 9.8
16
GSLM4 2008 09 19 12 13 160 5.1
GSLM4 2008 09 19 15 14 180 2.6
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
3/24/2010
GLERL Wave Model Shallow
17
07Z
2.5 km
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
07Z
5 km
3/24/2010
GLERL Wave Model Shallow
18
14Z
2.5 km
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
14Z
5 km
3/24/2010
Steady State Example
19
Steady State example in much better agreement with observations. 130 18 kts unstable.
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
3/24/2010
27 July 2009
20

Embarked East Tawas Coast Guard vessel at approximately 14Z.

Approximate 1 hr journeys to and from Gravelly Shoals, GSLM4

Return trip to East Tawas Coast guard station at 1630Z
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
3/24/2010
27 July 2009 - Nearshore Forecast
21
Outer Saginaw Bay
355 PM EDT SUN JUL 26 2009
.MONDAY...WEST WINDS 10 TO 15 KNOTS...TURNING TO SOUTHWEST. PARTLY
SUNNY. WAVES 1 TO 3 FEET...SUBSIDING TO AROUND 1 FOOT LATE.
940 PM EDT SUN JUL 26 2009
.MONDAY...WEST WINDS 10 TO 15 KNOTS...TURNING TO SOUTHWEST. PARTLY
SUNNY. WAVES 1 TO 3 FEET.
351 AM EDT MON JUL 27 2009
.TODAY...WEST WINDS 10 TO 15 KNOTS...BECOMING SOUTHWEST 5 TO 10
KNOTS...THEN INCREASING TO 10 TO 15 KNOTS DURING THE AFTERNOON.
PARTLY SUNNY. WAVES 2 TO 4 FEET.
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
3/24/2010
27 July 2009 - What Happened?
22
Tawas Bay
~ 1 foot
Tawas Pt. to Alabaster
~ 1 to 3 feet
Alabaster to Pt. Lookout
~ 3 to 4 feet
Pt. Lookout to Gravelly Shoal
~ 5 feet occasional 6 feet
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
3/24/2010
SBLM4 2009 07 27 09 00 277 5.6
SBLM4 2009 07 27 14 00 205 6.3
23
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
SBLM4 2009 07 27 12 00 241 6.5
SBLM4 2009 07 27 15 00 222 6.3
3/24/2010
GLERL Wave Model Shallow
24
15Z
2.5 km
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
15Z
5 km
3/24/2010
GLERL Wave Model Shallow
25
16Z
2.5 km
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
16Z
5 km
3/24/2010
Steady State Example
26
Steady State example in much better agreement with observations. 220 18 kts unstable.
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
3/24/2010
Short Case Study Summary
27




19 September 2008 – Models did not resolve stronger wind field from the
night before. This led to lower wave heights overnight and less residual wave
activity during the morning.
19 September 2008 – Steady state example in better agreement with
observations provides 4 ft wave heights near Saginaw Bay Light #1.
27 July 2009 – Again, weaker modeled wind field led to under-forecasted
wave heights.
27 July 2009 – Steady state example in better agreement with observations
provides for 5 ft wave heights near Gravelly Shoals.
Seemingly uneventful days can be far from it on the Lakes.
No substitute for correct wind field and stability!
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
3/24/2010
Future work
28



With higher resolution gridded wave height forecasts, what is
the best way to convey this information?
Wave height comparisons with new GLERL shallow water
modification, WaveWatchIII and Swan.
Three Dimensional Atmospheric Idealized Flow over the Great
Lakes
18th Annual Canada/US Great Lakes Operational Meteorology
Workshop (GLOMW)
3/24/2010