Surf Forecasting Tuesday November 22, 2011

Surf ForecastingSurf ForecastingTuesday November 22, 2011Tuesday November 22, 2011

Kurt KorteKurt Korte

ForecasterForecaster

Surfline.comSurfline.com

OutlineOutline

• Who Am I?Who Am I?• SurflineSurfline

– Company InfoCompany Info– ToolsTools

• Marine and Atmospheric ForecastingMarine and Atmospheric Forecasting– Tools AvailableTools Available

• Case StudiesCase Studies– Hurricane Katia – Aug/Sept 2011Hurricane Katia – Aug/Sept 2011– Southern Hemisphere Swell – Summer 2011Southern Hemisphere Swell – Summer 2011

• BathymetryBathymetry

Who Am I?Who Am I?

• Grew up in Virginia Beach, VAGrew up in Virginia Beach, VA

• Graduate of University of Virginia with a Graduate of University of Virginia with a degree in Environmental Science (2005)degree in Environmental Science (2005)– Atmospheric Sciences ConcentrationAtmospheric Sciences Concentration

• Graduate School at North Carolina State Graduate School at North Carolina State University (2008)University (2008)– Majored in MeteorologyMajored in Meteorology– Thesis Work involving African Easterly Waves over Thesis Work involving African Easterly Waves over

central/western Africa and the eastern Atlanticcentral/western Africa and the eastern Atlantic

How Did I Get Interested in How Did I Get Interested in Weather and Forecasting?Weather and Forecasting?

• SurfingSurfing

• Work = Less Time to SurfWork = Less Time to Surf

• Work + School = Even Less Time To SurfWork + School = Even Less Time To Surf

• Work + School + Sports = Almost No Work + School + Sports = Almost No SurfSurf

How Did I Get Interested in How Did I Get Interested in Weather and Forecasting?Weather and Forecasting?

• Know the weather and you can figure Know the weather and you can figure out when the waves will be goodout when the waves will be good

• Practice and school times were set, but Practice and school times were set, but I could make my own work scheduleI could make my own work schedule

• So, the better I was at forecasting, the So, the better I was at forecasting, the better I could make my schedulebetter I could make my schedule

How Did You Get Your Job?How Did You Get Your Job?

• LuckLuck– Against my normal advice, occasionally, Against my normal advice, occasionally,

it pays not to skip school and go on a it pays not to skip school and go on a surf tripsurf trip

• Within a week, I was hiredWithin a week, I was hired

Surfline – Early DaysSurfline – Early Days

• ““What if you could call a number any time of day and What if you could call a number any time of day and instantly get an up-to-the-minute report on surf instantly get an up-to-the-minute report on surf conditions at not only one location, but dozens at conditions at not only one location, but dozens at once? And what if you could get an honest-to-once? And what if you could get an honest-to-goodness seventy-two hour forecast of expected goodness seventy-two hour forecast of expected swells? The forecast, made by weather guru Sean swells? The forecast, made by weather guru Sean Collins, might be the most exciting feature of the Collins, might be the most exciting feature of the new Surfline. The advantages of actually knowing new Surfline. The advantages of actually knowing when a swell can be expected and from what when a swell can be expected and from what direction it will come need no explanation. Thanks to direction it will come need no explanation. Thanks to Surfline, a lot of Southern California surfers will be Surfline, a lot of Southern California surfers will be scoring better waves than they did in the past." scoring better waves than they did in the past." SURFING MagazineSURFING Magazine Spring 1985Spring 1985

Surfline – On the Path to Surfline – On the Path to TodayToday

• WavefaxWavefax– Late 1980sLate 1980s

• Surfline.comSurfline.com– 19951995

• First Live Surf CamFirst Live Surf Cam– Huntington Beach in February 1996 Huntington Beach in February 1996 – Followed by Pipeline cam later in 1996Followed by Pipeline cam later in 1996

Surfline TodaySurfline Today

• 100+ HD Cams100+ HD Cams

• Thousands of Surf SpotsThousands of Surf Spots

• Daily Surf ReportsDaily Surf Reports

• 7 and 14 day LOLA Forecasts7 and 14 day LOLA Forecasts

• Written ForecastsWritten Forecasts

• Point and Click Forecasts for anywhere in Point and Click Forecasts for anywhere in the worldthe world

• Editorial ContentEditorial Content

Surfline TodaySurfline Today

• In 2010In 2010

– Average of 142,000 unique people per Average of 142,000 unique people per dayday

– Average of 1,750,000 per month Average of 1,750,000 per month

Surfline Forecast TeamSurfline Forecast Team

• Written ForecastsWritten Forecasts– Expert forecast team with over a Expert forecast team with over a

combined 100 years of marine combined 100 years of marine forecasting experienceforecasting experience

– Forecast team includes:Forecast team includes:•Two PhD's in oceanography and ocean Two PhD's in oceanography and ocean

engineeringengineering

•US Navy wave modeling expertUS Navy wave modeling expert

•Eight ForecastersEight Forecasters

Tools on Surfline:Tools on Surfline:HD CamsHD Cams

Tools on Surfline:Tools on Surfline:7 Day LOLA Forecast7 Day LOLA Forecast

Tools on Surfline:Tools on Surfline:Nearshore AnimationsNearshore Animations



Tools on Surfline:Tools on Surfline:LOLA BuoysLOLA Buoys

Quick Buoy Case StudyQuick Buoy Case StudySurface Analysis Surface Analysis

LOLA BuoysLOLA Buoys NDBCNDBC

Comparison of Buoy ReadingsComparison of Buoy ReadingsNDBC vs Surfline’s LOLANDBC vs Surfline’s LOLA



BuoysBuoys

• Great tool for observations but also Great tool for observations but also verificationverification

• Unfortunately, you need buoys in the Unfortunately, you need buoys in the right places for them to be usefulright places for them to be useful

• A buoy that is only 25 miles or so off A buoy that is only 25 miles or so off the coast, though great for the coast, though great for observations, gives us little in the observations, gives us little in the way of forecast lead timeway of forecast lead time

Marine ForecastingMarine Forecasting

• Now that we have an idea of the Now that we have an idea of the some of the tools on Surfline, let’s some of the tools on Surfline, let’s look at some other tools and look at some other tools and information that is out there that can information that is out there that can help us make a solid forecasthelp us make a solid forecast

Marine and Atmospheric Forecasting:Marine and Atmospheric Forecasting:ModelsModels

• Atmospheric ModelsAtmospheric Models– Global Global

• NWS/Global Forecast System (GFS) NWS/Global Forecast System (GFS) • Navy Operational Global Prediction System (NOGAPS) Navy Operational Global Prediction System (NOGAPS) • United Kingdom Met Office model (UKMET)United Kingdom Met Office model (UKMET)• European Center for Medium-range Weather European Center for Medium-range Weather

Forecasting (ECMWF) Model Forecasting (ECMWF) Model

– Tropical CyclonesTropical Cyclones• NWS/Geophysical Fluid Dynamics Laboratory (GFDL) NWS/Geophysical Fluid Dynamics Laboratory (GFDL)

model model • NWS/Hurricane Weather Research and Forecasting NWS/Hurricane Weather Research and Forecasting

Model (HWRF) Model (HWRF)

Marine and Atmospheric Forecasting:Marine and Atmospheric Forecasting:ModelsModels

• NOAA WAVEWATCH IIINOAA WAVEWATCH III – Driven by winds from the operational GFSDriven by winds from the operational GFS– Winds are converted to 10m height assuming neutral Winds are converted to 10m height assuming neutral

stability (*assumption*)stability (*assumption*)– 1.25° x 1° resolution1.25° x 1° resolution– 4 model cycles (00z, 06z, 12z, 18z)4 model cycles (00z, 06z, 12z, 18z)

• With a 6h hindcast to assure continuity of swell With a 6h hindcast to assure continuity of swell – No wave data assimilation No wave data assimilation – Based on shallow water physics without mean currents Based on shallow water physics without mean currents – Sea Surface Temperatures as needed in the stability Sea Surface Temperatures as needed in the stability

correction for wave growth are obtained taken from the correction for wave growth are obtained taken from the Global Data Assimilation Scheme Global Data Assimilation Scheme

Marine and Atmospheric Marine and Atmospheric Forecasting:Forecasting:

ModelsModels• Western North Atlantic (WNA) regional Western North Atlantic (WNA) regional

model model – Obtains hourly boundary data from the global model Obtains hourly boundary data from the global model – 0°-50°N 98°-30°W Domain with 0.25° resolution 0°-50°N 98°-30°W Domain with 0.25° resolution

• North Atlantic Hurricane (NAH) regional North Atlantic Hurricane (NAH) regional modelmodel– Obtains hourly boundary data from the global model Obtains hourly boundary data from the global model – 0°-50°N 98°-30°W Domain with 0.25° resolution0°-50°N 98°-30°W Domain with 0.25° resolution– Wind fields are blended with GFDL hurricane winds Wind fields are blended with GFDL hurricane winds

when possible when possible

LOLA vs Wavewatch IIILOLA vs Wavewatch III

LOLALOLA

• Initializes with adjusted wind speeds Initializes with adjusted wind speeds from various global models from various global models

• Data AssimilationData Assimilation– Jason SatelliteJason Satellite– Buoy DataBuoy Data– Ship DataShip Data

• Takes into account how swells are Takes into account how swells are distorted by offshore islands and the distorted by offshore islands and the continental shelf continental shelf

• Nearshore ModelingNearshore Modeling– Finer resolution in the shallow water Finer resolution in the shallow water

environmentenvironment

Wavewatch IIIWavewatch III

• Initializes with winds from the Initializes with winds from the operational GFSoperational GFS

• No Data Assimilation No Data Assimilation

• Courser resolution limits ability to Courser resolution limits ability to properly propagate wave energyproperly propagate wave energy

– Course blocking put into modelCourse blocking put into model

• Minimum depth in model is 25m Minimum depth in model is 25m

So, by running our own models we have tremendous flexibility and So, by running our own models we have tremendous flexibility and resolution to accurately calculate surf heights for any point on Earth resolution to accurately calculate surf heights for any point on Earth

Remote SensingRemote Sensing

• Jason SatelliteJason Satellite– Continuous ocean surface Continuous ocean surface

topography measurements topography measurements that began in 1992 with that began in 1992 with the TOPEX/Poseidon the TOPEX/Poseidon satellite and continued satellite and continued with the Jason-1 satellite in with the Jason-1 satellite in 2001 2001

– Monitor the variation of Monitor the variation of the global mean sea level the global mean sea level and its relation to global and its relation to global climate change climate change

– Provide estimates of Provide estimates of significant wave height significant wave height and wind speeds over and wind speeds over the oceanthe ocean


• QuikSCATQuikSCAT– Launched 1999Launched 1999– Provided near-real-time Provided near-real-time

ocean- surface wind ocean- surface wind speed and direction speed and direction data over 90 percent of data over 90 percent of the global ocean every the global ocean every day day

– Roughly 1800 km wide Roughly 1800 km wide swath swath

– Died November 23, Died November 23, 2009 2009


• ASCATASCAT– 2007-Present2007-Present– 500 km wide swaths 500 km wide swaths – Measures up to ~95ktsMeasures up to ~95kts– Currently Operational Currently Operational – Less susceptible to rain Less susceptible to rain

flags than QuikSCATflags than QuikSCAT– Significant low bias at Significant low bias at

stronger wind speeds stronger wind speeds (over ~50kts)(over ~50kts)• Can be 10-15kts lower Can be 10-15kts lower

than QuikSCAT obs at than QuikSCAT obs at high wind speeds high wind speeds

ASCAT vs QuikSCATASCAT vs QuikSCATHurricane Hanna 2008Hurricane Hanna 2008

What are the major differences between the two?

Moving On…Moving On…

• Now that we have an idea of the Now that we have an idea of the tools that are out there, let’s review tools that are out there, let’s review some basic marine forecasting some basic marine forecasting principles and go from thereprinciples and go from there

Key Components to Wave Key Components to Wave Growth?Growth?

• Wind SpeedWind Speed

• Wind DurationWind Duration– How long the wind affects a given distanceHow long the wind affects a given distance

• Fetch or Fetch LengthFetch or Fetch Length– The distance over which the wind blows The distance over which the wind blows

from a constant direction and at a constant from a constant direction and at a constant speed speed

Since we already have a Since we already have a good handle on wind speed good handle on wind speed and duration, let’s take a and duration, let’s take a

look at identifying and look at identifying and locating fetches locating fetches

Determining Fetch Determining Fetch BoundariesBoundaries

• Need to find where the wind blows from Need to find where the wind blows from a constant direction and at a constant a constant direction and at a constant speedspeed

• Understanding how the fetch region is Understanding how the fetch region is changing or how many different fetch changing or how many different fetch regions exist can help the forecaster regions exist can help the forecaster confirm that the numerical wave models confirm that the numerical wave models are correct in their analysis and forecasts are correct in their analysis and forecasts


• When evaluating fetch, a forecaster When evaluating fetch, a forecaster only needs to be concerned with the only needs to be concerned with the fetches that will propagate waves fetches that will propagate waves into the forecast area into the forecast area

• There are no set guidelines to There are no set guidelines to determine the fetch boundary since determine the fetch boundary since changes in wind speed and direction changes in wind speed and direction can be fairly subtle over open water can be fairly subtle over open water


Determining Fetch BoundariesDetermining Fetch Boundaries

• Of course, the previous examples are Of course, the previous examples are a snapshot…in real time wind speed a snapshot…in real time wind speed and direction are constantly and direction are constantly changingchanging

• This can become very complicated, This can become very complicated, especially with a compact, intense especially with a compact, intense area of low pressure, such as a area of low pressure, such as a tropical cyclonetropical cyclone

Tropical CyclonesTropical Cyclones

• Obviously can be very strong with wind speeds in excess of 100kts Obviously can be very strong with wind speeds in excess of 100kts over a small areaover a small area

• Small but intense fetches develop due to the wind patterns around Small but intense fetches develop due to the wind patterns around low pressurelow pressure

• This leads to chaotic seas and a difficult forecastThis leads to chaotic seas and a difficult forecast– Models do a poor job Models do a poor job

• Lack of model resolution of strongest windsLack of model resolution of strongest winds– Lack of dependable observationsLack of dependable observations

• Who wants to be on a ship in the middle of a hurricane?Who wants to be on a ship in the middle of a hurricane?– Incorrect intensity initializations and forecastsIncorrect intensity initializations and forecasts

• If the initial conditions are incorrect, this can lead to extensive errors If the initial conditions are incorrect, this can lead to extensive errors through the forecast periodthrough the forecast period

• We will discuss this more later when we look at Hurricane KatiaWe will discuss this more later when we look at Hurricane Katia

Tropical CyclonesTropical Cyclones

• From an operational standpoint, it is From an operational standpoint, it is advantageous to divide the surface wind field advantageous to divide the surface wind field of an intense tropical cyclone into two parts of an intense tropical cyclone into two parts – Broad region of the cyclone that contains tropical Broad region of the cyclone that contains tropical

storm force winds capable of generating swell storm force winds capable of generating swell that can affect a large expanse of ocean and that can affect a large expanse of ocean and coastline coastline

– Second part is the wind field in and just outside of Second part is the wind field in and just outside of the eyewall. This more narrow area generates the eyewall. This more narrow area generates extreme seas and swell that propagate in a extreme seas and swell that propagate in a focused great-circle path. focused great-circle path.

Dynamic FetchDynamic Fetch

• When storm systems When storm systems move, waves in the right move, waves in the right quadrant, or right of track, quadrant, or right of track, may grow larger than may grow larger than expected because the expected because the waves are moving in the waves are moving in the same direction as the same direction as the advancing fetch advancing fetch

• Complicated because of Complicated because of the non-linear relationship the non-linear relationship between wind speed, between wind speed, duration, fetch and the duration, fetch and the storm speed, of the wave-storm speed, of the wave-generating cyclone generating cyclone

What’s It Take To Develop a What’s It Take To Develop a Major Swell? Major Swell?

• USS Kitty Hawk in the USS Kitty Hawk in the Western Pacific Western Pacific – Kitty Hawk is more than Kitty Hawk is more than

1,000 feet long and the 1,000 feet long and the deck is about 40 feet deck is about 40 feet above the ocean above the ocean surface surface

• Winds: 40-50 knots. Winds: 40-50 knots. Seas: 35-45 feet.Seas: 35-45 feet.

What Kind of Surf Would This What Kind of Surf Would This Storm Send Us? Storm Send Us?

• We expect significant swell decay within the We expect significant swell decay within the first 1000 miles and a slower rate of decay first 1000 miles and a slower rate of decay after 2000 miles from the storm fetchafter 2000 miles from the storm fetch

• For Most Surf Spots:For Most Surf Spots:– Estimated Surf 1000 miles away: 15-30 foot+ Estimated Surf 1000 miles away: 15-30 foot+

facesfaces– Estimated Surf 2000 miles away: 12-20 foot facesEstimated Surf 2000 miles away: 12-20 foot faces– Estimated Surf 4000 miles away: 8-12 foot facesEstimated Surf 4000 miles away: 8-12 foot faces– Estimated Surf 5000 miles away: 6-10 foot facesEstimated Surf 5000 miles away: 6-10 foot faces

Creating A ForecastCreating A Forecast

• Whenever doing a forecast, the first Whenever doing a forecast, the first question you should ask yourself is:question you should ask yourself is:

What is happening right now?What is happening right now?

How To Make A ForecastHow To Make A Forecast• Look Outside!Look Outside!

– If it is a short term If it is a short term forecast you can learn a forecast you can learn a lot about what is going lot about what is going on outsideon outside

– Is it raining? Cloudy? Is it raining? Cloudy? Snowing? Hail? Snowing? Hail? Lightning?Lightning?

• Take a look at regional Take a look at regional observationsobservations– Look ‘Upstream’Look ‘Upstream’

How to Make a ForecastHow to Make a Forecast

• Other types of observational dataOther types of observational data– Remote SensingRemote Sensing

•RadarRadar•Satellite Derived WindsSatellite Derived Winds•Altimetry Altimetry

– Satellite ImagesSatellite Images

– Upper Air Data UpstreamUpper Air Data Upstream

How To Make A ForecastHow To Make A Forecast

Creating A ForecastCreating A Forecast

• As we have seen, observations are As we have seen, observations are crucialcrucial– Unfortunately, the observational network Unfortunately, the observational network

over the ocean is scarce, at bestover the ocean is scarce, at best

• What tools do we have available?What tools do we have available?•SatellitesSatellites•Buoy DataBuoy Data•Ship ObservationsShip Observations•Nearshore Observations (ie checking the surf)Nearshore Observations (ie checking the surf)

Case Study – Hurricane Case Study – Hurricane KatiaKatia


• Formed from a strong Formed from a strong tropical wave in the tropical wave in the far eastern Atlantic on far eastern Atlantic on August 29August 29thth

• Peaked in intensity Peaked in intensity late on September 5late on September 5thth

• Came to within 330 Came to within 330 nautical miles from NJnautical miles from NJ


• Major HurricaneMajor Hurricane– Category 4Category 4– Maximum winds of Maximum winds of

115kts115kts

• Classic Cape Verde Classic Cape Verde Hurricane TrackHurricane Track

• Delivered solid surf Delivered solid surf to the Caribbean to the Caribbean and East Coastand East Coast


• Complicated pattern Complicated pattern was in place over was in place over the eastern USthe eastern US

• Frontal boundary Frontal boundary approaching the approaching the East CoastEast Coast

• Remnants of Remnants of Tropical Storm Lee Tropical Storm Lee that made landfall that made landfall along the Gulf Coastalong the Gulf Coast


• As with any system over the ocean, As with any system over the ocean, there are uncertainties that can there are uncertainties that can result in a blown forecastresult in a blown forecast– Wind SpeedWind Speed

•Maximum windsMaximum winds

•Wind radiiWind radii

– Current Sea StateCurrent Sea State– Intensity forecastIntensity forecast


• As mentioned before, some of the more As mentioned before, some of the more important tools we have over the open important tools we have over the open ocean are satellite derived data, ocean are satellite derived data, specially ASCAT and Jason satellite dataspecially ASCAT and Jason satellite data

• These observations give us a good These observations give us a good indication of how the model is indication of how the model is performing so forecasts can be fine performing so forecasts can be fine tunedtuned

ASCAT Passes of Hurricane ASCAT Passes of Hurricane KatiaKatia

Jason Satellite Passes of Jason Satellite Passes of Hurricane KatiaHurricane Katia


• Some of the regional Some of the regional buoys were down due to buoys were down due to Hurricane IreneHurricane Irene

• Notice the difference in Notice the difference in swell height and timing swell height and timing between the East Hatteras between the East Hatteras buoy (top) and the VB buoy (top) and the VB buoy (bottom)buoy (bottom)

• Why the quick drop in Why the quick drop in swell size on Thursday?swell size on Thursday?


• For the Delaware Bay buoy, notice the 15-16” For the Delaware Bay buoy, notice the 15-16” swell energy peaked at around 8 feet, indicating swell energy peaked at around 8 feet, indicating significant decay from our offshore observationssignificant decay from our offshore observations

• Quick drop through the day on FridayQuick drop through the day on Friday

Case Study – Southern Case Study – Southern Hemisphere SwellHemisphere Swell

• First off, yes the First off, yes the East Coast can and East Coast can and does see long does see long period Southern period Southern Hemisphere swellsHemisphere swells

• Typical during the Typical during the summer monthssummer months

• From strong storm From strong storm activity off South activity off South AfricaAfrica


• Infrequent because of the typical Infrequent because of the typical west to east storm movementwest to east storm movement

• Significant decay ratesSignificant decay rates

• Let’s take a look at a ‘strong’ Let’s take a look at a ‘strong’ Southern Hemisphere event that Southern Hemisphere event that happened a few years agohappened a few years ago



• Strong low pressure took shape to the Strong low pressure took shape to the SW of South AfricaSW of South Africa

• Blocking high pressure SE of South Blocking high pressure SE of South Africa Africa

• High pressure building into the central High pressure building into the central south Atlanticsouth Atlantic


• We could go through, define the We could go through, define the fetch region and calculate, using the fetch region and calculate, using the wave nomograms, the wave height wave nomograms, the wave height and period of the swell propagating and period of the swell propagating from this system, but for brevity, from this system, but for brevity, let’s just do a little hindcasting…let’s just do a little hindcasting…



• Using the Surfline Using the Surfline Hurricanetrak swell Hurricanetrak swell ruler, we can see that ruler, we can see that a swell coming from a swell coming from this area would take 9 this area would take 9 days and 6hrs to get days and 6hrs to get to the NJ coastlineto the NJ coastline– 10 days 7hrs for 18” 10 days 7hrs for 18”

energyenergy– 11 days and 13hrs for 11 days and 13hrs for

16” energy16” energy– 13 days and 5hrs for 13 days and 5hrs for

14” energy14” energy


• Now, we can Now, we can compare that data to compare that data to the buoys readings the buoys readings along the East Coast along the East Coast

• Keep in mind the Keep in mind the storm peaked in storm peaked in intensity on the intensity on the 44thth/5/5thth before before weakening on the weakening on the 6th 6th


• Notice how many Notice how many days the swell was days the swell was in the waterin the water

• Why does the swell Why does the swell period steadily period steadily decrease through decrease through time? time?

Bathymetry Bathymetry

• The measurement of depths of water The measurement of depths of water in oceans, seas, and lakes. The in oceans, seas, and lakes. The topography of the ocean floor or topography of the ocean floor or underwater bottom underwater bottom

• In addition to the continental shelf, In addition to the continental shelf, which is located off the US East which is located off the US East Coast, NJ and NY also have the Coast, NJ and NY also have the Hudson Shelf and Hudson CanyonHudson Shelf and Hudson Canyon

Bathymetry Bathymetry

About Hudson Shelf About Hudson Shelf

• The geological coastline more than 20,000 years The geological coastline more than 20,000 years ago when ocean levels were lower due to the ice ago when ocean levels were lower due to the ice ageage

• In the middle of the Shelf is the Hudson Canyon, In the middle of the Shelf is the Hudson Canyon, which extends southeastward towards the end of which extends southeastward towards the end of the continental shelf nearly 100 miles offshorethe continental shelf nearly 100 miles offshore

• The Canyon is actually the ancient extension of The Canyon is actually the ancient extension of the Hudson River the Hudson River

• The portion of the Canyon closest to the shore is The portion of the Canyon closest to the shore is call the Hudson Valley – this is the portion of the call the Hudson Valley – this is the portion of the Canyon that will have the most effect on the surf Canyon that will have the most effect on the surf for NY and NJfor NY and NJ

Swell GrowthSwell Growth

Swell GrowthSwell Growth

Bathymetry and Wave Bathymetry and Wave PeriodPeriod• The longer period the swell, the deeper the The longer period the swell, the deeper the

energy will extend downward in the ocean energy will extend downward in the ocean

• Long period swell extends much deeper than Long period swell extends much deeper than short period swell and thus, given the same short period swell and thus, given the same depth of ocean at an arbitrary point, the depth of ocean at an arbitrary point, the longer period swell will be more affected by longer period swell will be more affected by the bottom than the shorter period swell the bottom than the shorter period swell

Bathymetry and Wave Bathymetry and Wave PeriodPeriod• As the long period swell approaches the shallower depths of As the long period swell approaches the shallower depths of

the region, the waves will begin to feel the bottom and the region, the waves will begin to feel the bottom and refractive and attenuation processes will take place sooner refractive and attenuation processes will take place sooner than for a shorter period swell than for a shorter period swell

• This does two things to the swell:This does two things to the swell:– Change the direction of the initial incident angle of the swell Change the direction of the initial incident angle of the swell

(refractive process)(refractive process)– Attenuation of swell energy due to the continental shelf Attenuation of swell energy due to the continental shelf

Thus various swells will behave differently in your region Thus various swells will behave differently in your region dependent upon the incident angle of the swell and the dependent upon the incident angle of the swell and the

swell periodswell period

Impact of Swell Direction and Impact of Swell Direction and Period along the NY/NJ Period along the NY/NJ

coastlinecoastline


coastlinecoastline• Shorter wave periods, because they don’t Shorter wave periods, because they don’t

‘feel’ the bottom of the Hudson Valley ‘feel’ the bottom of the Hudson Valley finger, are not significantly refractedfinger, are not significantly refracted

• Longer period energy (14-20”) will be Longer period energy (14-20”) will be impacted by the Hudson Shelf and Canyon impacted by the Hudson Shelf and Canyon and this leads to refraction that may and this leads to refraction that may prevent the waves from approaching into prevent the waves from approaching into the Valley fingerthe Valley finger– This system leads to smaller wave heights for This system leads to smaller wave heights for

spots in Northern NJ and far western LI during spots in Northern NJ and far western LI during long period SE swell eventslong period SE swell events


coastlinecoastline• In conclusion:In conclusion:

– Obviously a complicated issue along any Obviously a complicated issue along any coastline but especially herecoastline but especially here

– Changes in the bathymetry in the Changes in the bathymetry in the nearshore environment will also have an nearshore environment will also have an impact on what spots do best with longer impact on what spots do best with longer period swell energyperiod swell energy

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Surf Forecasting Tuesday November 22, 2011