Cult of Climatology:
  Part 4 in Series:  Timing is Everything

It was a drunken summer night on the Jersey shore when four surfers were overcome by a shady, alcohol-induced judgment call.  Lavallette native Mike Wright was working the bar that infamous evening, and  some of the surfing crew were unduly benefiting from multiple free beverages that would eventually lead to their demise.  Around 1 a.m., the rowdy beneficiaries finally convinced their fellow patrons to switch the TV to the Weather Channel, a formidable task in a room full of intoxicated Mets fans.    Then a twinkle arose in each of the surf-starved right coastersí eyes as John Hope pointed to a newly formed tropical storm that was brewing just east of Hatteras.  Another round of beers hit the bar in celebration as Chris, Mike,  Chad, and some guy named Al pondered the impending juicy  swell. Then the moment of truth came as Chad blurted out, "Let's drive  to Hatteras!"  

Before the magnitude of their decision had even registered, our heroes had downed their beers, found a designated driver, and begun strapping four quivers onto Chad's roof.  A little karma didn't even stop them hours later in Virginia when Chad's voice was heard a second time--this time much softer--as he calmly slurred: "There they go."  Three heads turned just as all the boards took off 747-style and scattered across the freeway.  (Miraculously , only Chris' boards sustained any damage and a few dings will never keep a Cape Cod kid from getting as many barrels as humanly possible.) Finally, around 9 a.m., this hungover hoard of Yankees rolled out onto the Atlanticís best sandbar to reap the rewards of their labors--perfect, peeling, thigh-high Hatteras ground swell.  They surfed for an hour or so, accepted the new record for worst skunking ever, and then cruised back up north to their humble abodes.  The next day the Outer Banks was bulging with well-overhead, reeling barrels.   Perhaps a little more knowledge of swell travel time--and a few less beers--would have assisted these unlucky Yanks in their surfari.  

In the last three issues, The Cult has looked at surf forecasting methods and swell-producing systems.  You now have the basis for predicting surf and an understanding of the necessary ingredients that add up to getting in the water.  Now itís time to step up the difficulty level and cross over into a new frontier: What happens when the swell has been produced and is traveling  out of the system and hopefully towards you?  When will it get there and what should we expect for conditions upon its arrival?  

As with any type of forecasting, at some point some serious guesswork will come into play.  So before we start, keep in mind that despite the incorporation of several scientific looking parameters and equations, this area of surf forecasting  features more gray areas than Jerry Garciaís beard.   After all, we arenít dealing with a uniform ocean or coastline and the number of variables make it an imperfect science.  However, the more you forecast and adjust your predictions with precise  consideration of  both the region you are dealing with and past experience,  the more accurate your forecasting will become--and, even then, youíre still gonna blow it sometimes.  

First we'll take a look at swell travel.  Before you get freaked out by all the numbers and decimal points, let me stress that anyone who passed elementary school math is capable of  predicting a swellís arrival time successfully. (When I say ìsuccessfullyî, Iím satisfied if I call it within six hours.)  In order to figure out how fast a swell is moving, first we need to know some basic data.  This is perhaps the most difficult part of the equation because often there is no direct source of this data, such as a buoy or ship report.  Regardless, the easiest and most direct way of determining swell speed is by finding the period of the waves exiting the system.  If you are lucky enough to be tracking a swell that is originating or traveling through an area with automated offshore buoys, you can access detailed buoy information via the internet [http://www.nws.fsu.edu/buoy/] and find out exactly what the period of the swell is.   

If this is not the case, you must make an assumption as to what you think the period may be.  When confronted with the latter scenario I find the best solution is to use the National Weather Service/NOAA marine charts which can also be found on the internet [http://weather.noaa.gov/fax/marsh.shtml].  With this information you can retrieve two possible sources of useful information for determining wave period.  The first is a ship report from the area that is producing the swell  heading towards you.  These ship reports always give a wind velocity.  If there are no ship reports, you can use the predicted wind velocity given by the storm maps as your basis.  (If you remember from Cult #1, each barb on the wind indicator represents 10 knots of wind and each half barb is 5 knots.) Once you have an estimated wind speed, the other factor to consider is fetch.  At least 150 miles of fetch is usually necessary to produce some  juice.  Youíll need to look at the marine map and measure the distance by hand or eye--just follow the isobars that show favorable winds and size it up to see if the fetch is adequate.  

Once you have an idea of the wind velocity for the swell-producing area (within 5 knots) and are confident the fetch is adequate for significant wave production, you can resort to the following chart [Fig. A] to estimate the probable period of the swell.  Once again, this is not an exact science.  Some storms might closely match the chartís criteria, increasing accuracy.  In other cases, the numbers might be totally awry and any prediction becomes a crap shoot.  The trickiest aspect of the chart is that itís numbers are geared to fully developed seas, and the higher wind speeds correlate with incredible wave heights; however, hurricanes almost never form fully developed seas so if the wind speed is right, and there is adequate fetch and storm duration, weíre generally in business.  (Also those incredible wave heights are at the point of origin; later weíll incorporate an equation to estimate the wave-size upon arrival.)  As usual, the best advice here is: practice makes perfect.  The more you employ your forecasting abilities and incorporate your experiences into your guesswork, the less confusing the process and the more confident you will be in your forecasting.  

Minimum duration is for the minimum amount of time required for these conditions to develop.  significant period is the period of the significant waves.  wave length is from crest to crest.  heights are heights.