Transcript Presentation - Nathan Cool

Surf Forecasting Simplified
In search of the perfect session using modern technology
Nathan Cool
www.NathanCool.com
This presentation and accompanying material at:
www.nathancool.com/lmu
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
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
Old School
Tight isobars
How we did it back in the day...
Pressure Maps, Buoys, and NOAA radio...
...and yes...I once had hair...
1987...skipping work...
The Tools of the Trade Today
How the Internet changed everything
Wave Analysis Models (WAMs)
Model Data
Weather Models
Wave Analysis Models (WAMs)
Your Tax Dollars at Work
• FNMOC
• NOAA
• NWS
Date
Dissecting a WAM
Wave Heights
Forecast
Date
Heights
Scale/Key
Date
Dissecting a WAM
Periods
Forecast
Date
Periods
Scale/Key
The WAM Crystal Ball
A model look at the future
Today
Tomorrow
48 Hours
144 Hours
Weather Models
Your Tax Dollars, Still At Work
• FNMOC
• NOAA
• NWS
WAM Raw Data
Grabbing the middle-man
How LOLA, SwellWatch, WaveWatch and others do it
Data
Monitoring
Mechanisms
• Wind data (wind fields)
• Sea surface temperatures
• Ice concentrations
• Bathymetry/obstruction data
Model
WAM Raw Data
Number Crunching Behind the Scenes
For any point on the planet
(“Virtual” Buoys)
Thus….
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
A Swell is Born
Slide-Shows: Surf forecasting from start to finish
1. Low Pressure Forms
3. Fetch is created
(slide show)
(slide show)
2. Winds Increase
(slide show)
4. Swell Travels to Coast
(slide show)
Forecasting the Swell
Two examples: Winter NW, and Summer SW
The essentials
• Distance
• Angle
• Trajectory
• Wave Height
• Period
A Note About Accuracy
Time and Size
Calculations
Minutes, Seconds, Inches
(modeling)
Hours, Feet
(surf forecasting)
Forecast Tolerance
Distance
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...
www.WaveCast.com/calculator
Northern Hemi Numbers
• Distance: ~2700 nm
• Angle (A): ~285°
• Trajectory (T): ~20°
• Wave Height: ~40 feet
• Period: 20 seconds
T
A
270
~210
180
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
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
Northern Hemi Numbers
• Distance: ~2700 nm
• Angle (A): ~280°
• Trajectory (T): ~20°
• Wave Height (Wh): ~40 feet
• Period (p): 20 seconds
A
T
• 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) * 0.85 = 6.8'
Face Height = 6.8 * (20 * 0.1) = ~13.6' (best case)
Time = 2700 nm / (20 * 1.5) = 90 hours (~3.75 days)
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
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
When the waves arrive...
Obstructions & Island Shadowing in SoCal (1 of 2)
Obstruction
Energy Skirts Past SoCal
Islands Block Energy Also
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
When the waves arrive...
1/22/2011
• No loss from angular decay
• No obstructions
• Size amplified by refraction
Jacob Trette
Moments before going
over the falls at Mavs.
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
270
~210
180
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
• 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)
Indicators
Near-term verification by buoys
Indicators
Near-term verification by CDIP
9-Period Bands
Buoy history
Now-cast Model
But, initialized at Pt. Conception
Seasonal Forecasting
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
Seasonal Forecasting
ENSO : El Niño 1997-98
Seasonal Forecasting
ENSO : El Niño's effect on the jetstream : the results, 1998
Seasonal Forecasting
ENSO : This year's La Niña
Jetstream/
storm track
Strong high
pressure
Seasonal Forecasting
ENSO : La Niña and Omega Blocking
Seasonal Forecasting
Southern Hemi Jetstream
Bend in jetstream
guides storms/swells
Conditions to Consider
Wind Swell
Pressure
Fetch
Wind
Conditions to Consider
Coastal Eddy, Southerly Winds, Onshore Flow
Pressure
Wind
Northerly Winds
Coastal Eddy
Trapped Between
Islands and Land
Conditions to Consider
Santa Ana, when the low passes and high takes over
High circulating clockwise
as low moves east
Offshore winds
Conditions to Consider
Santa Ana, thermal gradients
Normal Thermal Gradients
Tight Thermal Gradients
Thank You!
Q&A
www.NathanCool.com/lmu
• Presentation
• Swell Calculator (Excel)
• Forecast Discussion Group