1. Surf Forecasting Simplified
In search of the perfect session using modern technology
Nathan Cool
This presentation and accompanying material at: 1

2. Agenda The pebble in the pond, forecasting principle
Tools of the trade:
WAMs
Data Mining
Weather models
WAMs in-depth
Forecast Accuracy
Dissecting data (automatic data mining)‏
Forecasting examples
Near-term swell verification
Seasonal Surf Forecasting
Conditions to Consider
Q&A and web resources 2

3. Ripples across the ocean
The Pebble and the Pond
Ripples across the ocean
The Principle
Wind (the pebble)‏
Transfers energy to water
Waves are created
Travel outward
Eventually reaching shore
The Practice
Track ocean storms
Measure energy
Measure distance to shore
Wax your board 3

4. Old School Tight isobars How we did it back in the day...
Pressure Maps, Buoys, and NOAA radio...
...and yes...I once had hair...
Tight isobars
skipping work... 4

5. The Tools of the Trade Today
How the Internet changed everything
Wave Analysis Models (WAMs)‏
Model Data
Weather Models 5

6. Wave Analysis Models (WAMs)‏
Your Tax Dollars at Work
FNMOC
NOAA
NWS 6

7. Dissecting a WAM
Wave Heights
Date
Forecast Date
Heights
Scale/Key 7

8. Dissecting a WAM
Periods
Date
Forecast Date
Periods
Scale/Key 8

9. A model look at the future
The WAM Crystal Ball
A model look at the future
Today
Tomorrow
48 Hours
144 Hours 9

10. Weather Models
Your Tax Dollars, Still At Work
FNMOC
NOAA
NWS 10

11. WAM Raw Data Grabbing the middle-man
How LOLA, SwellWatch, WaveWatch and others do it
Data
Monitoring Mechanisms
Model
Wind data (wind fields)‏
Sea surface temperatures
Ice concentrations
Bathymetry/obstruction data 11

12. Thus…. WAM Raw Data Number Crunching Behind the Scenes
For any point on the planet
(“Virtual” Buoys)‏
Thus…. 12

13. WAM Raw Data Making a near-shore chart Data Charts
(Near-shore estimates)‏
Monitoring Mechanisms
Wind data (wind fields)‏
Sea surface temperatures
Ice concentrations
Bathymetry/obstruction data 13

14. Slide-Shows: Surf forecasting from start to finish
A Swell is Born
Slide-Shows: Surf forecasting from start to finish
1. Low Pressure Forms
(slide show)‏
2. Winds Increase
(slide show)‏
3. Fetch is created
(slide show)‏
4. Swell Travels to Coast
(slide show)‏ 14

15. Two examples: Winter NW, and Summer SW
Forecasting the Swell
Two examples: Winter NW, and Summer SW
The essentials
Distance
Angle
Trajectory
Wave Height
Period 15

16. A Note About Accuracy Calculations Forecast Tolerance
Time and Size
Calculations
Minutes, Seconds, Inches
(modeling)‏
Hours, Feet
(surf forecasting)‏
Forecast Tolerance 16

17. Distance Or the easy way... www.WaveCast.com/calculator
Where in the heck am I ???
Curvature of the Earth has to be accounted for
Haversine formula
Distance in nautical miles
R = earth’s radius (mean radius = 6,371km) Δlat = lat2 − lat1 Δlong = long2 − long1 a = sin²(Δlat/2) + cos(lat1).cos(lat2).sin²(Δlong/2) c = 2.atan2(√a, √(1−a)) d = R.c
=((DEGREES(ACOS(SIN(RADIANS(Lat1))*SIN(RADIANS(Lat2))+COS(RADIANS(Lat1))*COS(RADIANS(Lat2))*COS((RADIANS(Lon2-Lon1)))))*69.09))*0.87
Or the easy way... 17

18. Northern Hemi Numbers Distance: ~2700 nm Angle (A): ~285°
Trajectory (T): ~20°
Wave Height: ~40 feet
Period: 20 seconds T A
270
~210
180 18

19. Decay Factor (distance)‏
Running the Numbers
Decay Factor (distance)‏
Decay = (90-((LOG2(Distance)) * (2π)))/100
=(90-((LOG(A2;2))*(2*PI())))/100
Where A2 is the distance in nautical miles 19

20. Angular Spreading Decay Factor (Trajectory)‏
Running the Numbers
Angular Spreading Decay Factor (Trajectory)‏
Approx: (100–(θ*0.9))/100
...or: ((90–θ)+15)/100
0° = no loss
20° = ~15% loss
45° = ~40% loss 20

21. Northern Hemi Numbers Distance: ~2700 nm Angle (A): ~280°
Trajectory (T): ~20°
Wave Height (Wh): ~40 feet
Period (p): 20 seconds T A
Distance Decay (dd) = ~80%
Angular Decay (ad) = ~15%
Height (h) = ((Wh – dd) – ad)‏
Face Height = h * (p * 0.1)‏
Time = Distance / (p * 1.5)‏
Height = (40’ – 80%) - 15% = 6.8’
(40 * 0.2) * = 6.8'
Face Height = 6.8 * (20 * 0.1) = ~13.6' (best case)‏
Time = 2700 nm / (20 * 1.5) = 90 hours (~3.75 days)‏ 21

22. Shoaling Considerations
When the waves arrive...
Shoaling Considerations
6.8' seas * (20 * 0.1) = ~13.6' face max
Face Height Approximations
Steep Shoaling: h * (p * 0.1)‏
Slow-sloped Shoaling: h * (p * 0.075)‏
So…
Steep Shoaling: = 6.8 * 2.0 = ~13.6' face height
Slow-sloped Shoaling) = 6.8 * 1.5 = ~10.2' face height 22

23. Shoaling Considerations: Tidal Depth
When the waves arrive...
Shoaling Considerations: Tidal Depth
Tides, depth, conditions,
change hour to hour
Normal, Average Tides
Abnormal “Tidal Swing”, from lunar event
7' depth difference
over 8 hours 23

24. When the waves arrive...
Obstructions & Island Shadowing in SoCal (1 of 2)‏
Obstruction
Energy Skirts Past SoCal
Islands Block Energy Also 24

25. Obstructions & Island Shadowing in SoCal (2 of 2)‏
When the waves arrive...
Obstructions & Island Shadowing in SoCal (2 of 2)‏
More swell north of
Pt. Conception, less
swell in SoCal...
...due to NW angle 25

26. When the waves arrive... No loss from angular decay No obstructions
1/22/2011
No loss from angular decay
No obstructions
Size amplified by refraction
Jacob Trette
Moments before going
over the falls at Mavs. 26

27. Tracking A Southern Hemi
From the Southern Ocean to SoCal
Distance: ~5200 nm
Angle (A): ~210°
Trajectory (T): ~45°
Wave Height: ~36 feet
Period: 15 seconds A
To SoCal T
Trajectory
270
~210
180 27

28. Tracking A Southern Hemi
The Numbers for SoCal
Distance: ~5200 nm
Angle (A): ~210°
Trajectory (T): ~45°
Wave Height (Wh): ~36 feet
Period (p): 15 seconds A
To SoCal T
Trajectory
Distance Decay (dd) = >85%
Angular Decay (ad) = ~30%
Height (h) = ((Wh – dd) – ad)‏
Face Height = h * (p * 0.1)‏
Time = Distance / (p * 1.5)‏
Height = (35’ – 85%) - 30% = 3.7'
Face Height = 3.7 * (15 * 0.1) = 5.5 feet
Time = 5200 nm / (15 * 1.5) = 231 hours (~ 9 days)‏ 28

29. Near-term verification by buoys
Indicators
Near-term verification by buoys 29

30. Indicators Near-term verification by CDIP Now-cast Model
But, initialized at Pt. Conception
9-Period Bands
Buoy history 30

31. Seasonal Forecasting La Niña: El Niño: Winter (good)‏
ENSO
El Niño:
Winter (good)‏
Low pressure dominates Gulf
Improves storm track
Summer (bad)‏
Stronger southern hemi jetstream
Less chance for storms to drift north
More Pacific hurricanes
Blows out Atlantic hurricanes
La Niña:
Winter (bad)‏
High pressure blocking in Gulf
Less favorable storm track
Summer (good)‏
Weaker southern hemi jetstream
Better chance for storms to drift north
Fewer Pacific hurricanes
Better chance for Atlantic hurricanes 31

32. Seasonal Forecasting
ENSO : El Niño 32

33. ENSO : El Niño's effect on the jetstream : the results, 1998
Seasonal Forecasting
ENSO : El Niño's effect on the jetstream : the results, 1998 33

34. ENSO : This year's La Niña
Seasonal Forecasting
ENSO : This year's La Niña
Jetstream/
storm track
Strong high
pressure 34

35. ENSO : La Niña and Omega Blocking
Seasonal Forecasting
ENSO : La Niña and Omega Blocking 35

36. Southern Hemi Jetstream
Seasonal Forecasting
Southern Hemi Jetstream
Bend in jetstream
guides storms/swells 36

37. Conditions to Consider
Wind Swell
Pressure
Wind
Fetch 37

38. Conditions to Consider
Coastal Eddy, Southerly Winds, Onshore Flow
Pressure
Wind
Northerly Winds
Coastal Eddy
Trapped Between
Islands and Land 38

39. Conditions to Consider
Santa Ana, when the low passes and high takes over
High circulating clockwise
as low moves east
Offshore winds 39

40. Conditions to Consider
Santa Ana, thermal gradients
Tight Thermal Gradients
Normal Thermal Gradients 40

41. Q&A Thank You! www.NathanCool.com/lmu Presentation
Swell Calculator (Excel)‏
Forecast Discussion Group 41