Click Here to Visit Surf Images!
Click Here to Visit Vunabaca!
> VIDEO SURF FORECAST For Sun (10/19) HERE - - - 'BIG WAVE HELLMEN Reruns' Times & Channels - HERE
Buoys | Buoy Forecast | Models | Pacific Forecast | QuikCAST | Chartroom | El Nino | Tutorials | Reports | Great Circles | News | Video

Create Your Own Surf Forecast
Works anywhere on the planet!

 

You probably track open ocean weather systems using satellite photos, models, and have a good intuitive sense of which storms or conditions have capacity to generate a swell. But once the system is forecast or actually forms, how can you increase certainty that a swell will be headed your way? And how can you predict when that swell will hit?

Here's a step-by-step process to help answer those questions:

  1. Look for a storm and verify it will be in your swell window.
    Regularly review atmospheric models that depict both surface pressure and winds (like the AVN or MRF). Look for periods when winds are forecast to blow in excess of 25 kts towards your beach for longer than 24 hours. Then verify that the winds are forecast to be positioned within your swell window (see below). The best situation is to have high winds, covering a large fetch area, blowing at you for a long time. But only experience will determine what the requirements are for your beach.

    A 'swell window' is the part of your ocean that provides a swell unobstructed, straight-line access to your beach (even 1000 miles or more away). Get a globe. Locate your beach. Identify islands, shoals, land, or anything that could obstruct a swell from proceeding straight into your beach. Using a string and a pin, tie the string to the pin, and stick the pin into the globe on your beach. Using the string as a guide, pull it tight and out into the ocean away from your beach. Move the string in different directions along the surface of the globe. Wherever the string first touches the edge of land (or anything that would obstruct a swell), trace the line of the string onto the globe using a pen. If you have access to "Great Circle" charts, use them instead. All beaches will have at least 2 boundaries to their swell window, and if islands are present, perhaps many more.

  2. Record Storm Data on Storm Profile Worksheet.
    Print out a stack of Storm Profile Worksheets (view at a medium font and print). When a storm is first predicted, review the wave models and write down the date and positions of the center of the highest seas aimed at or near your beach (latitude and longitude) on the top half of the worksheet (see sample below). Try to be as accurate as possible. Also record the heights of the highest seas aimed at your beach, swell vector/headings and relative fetch area size. Here's an example of what the data should look like:

    Day & Time Forecast or Confirmed Highest Sea Aimed at Your Position
    (Latitude - Longitude)
    Max Sea Height Main Swell Vector Aimed At: Fetch Area Size
    (Small/Med/Large)
    Wed AM Confirmed 45 N 175 W 26 ft Washington Small
    Wed PM Confirmed 44 N 170 W 31 ft Oregon Moderate
    Thurs AM Forecast 42 N 163 W 36 ft N. CA Large
    Thurs PM Forecast 40 N 155 W 33 ft S. CA Moderate
    Fri AM Forecast 38 N 150 W 22 ft Mexico Small and Fading


  3. Confirm the storm is producing sufficient winds to generate High Seas.
    Once the storm has formed, view QuikSCAT or SSM/I satellite based wind sensor data to confirm actual wind speed and headings
    . Again, verify those winds are in your swell window and pointed towards your beach. If you need links for this data, select your ocean (Atlantic, Indian, Pacific) and select one of the links under the heading 'Satellite Observed Winds'.

  4. Update Storm Profile Worksheet.
    Once the storm actually develops, update the worksheet religiously, being sure to record data from all '00hr' or 'Current' images from the wave model during the storms lifecycle. Most wave models are updated every 12 hours. The '00hr' image reflects the actual state of the ocean while other images depict forecast conditions. Only the '00hr' image is reliable. If you need links for this data, choose your ocean (Atlantic, Indian, Pacific) and within that page, select one of the links under the heading 'Satellite Observed Waves'.

  5. Calculate Swell Arrival Time Using Swell Arrival Time Calculator
    Note: Your browser must be either Netscape or Internet Explorer version 4.0 or higher and you must install an appropriate "Virtual Machine/Java Runtime Environment (JRE) for the Swell Arrival Calculator to work right. See details below (in small print) to obtain and install a virtual machine. If you're not using one of these browsers, you're on your own.

    Once the storm is starting to fade and you have confirmed sea heights for the balance of the storm life, figure out when the swell will hit. To do this, enter the coordinates of your beach (or a local buoy), the storm start date/time, and the coordinates of the the highest sea heights and the actual seas height measurements from your worksheet (from Step 2) into the Swell Arrival Time Calculator. Click on "Determine Swell Arrival Time" and the tool will do it all for you. You're done! Skip to Step 11. If you can't use the Calculator, keep reading.

    To obtain a a free "virtual machine/JRE environment" (7.6 meg), navigate to http://java.sun.com/getjava/ Read the details on the page to make sure it works with your operating system. If you're running any recent version of Windows, Solaris or Linux just hit the Free Download button a the top of the page. Follow the prompts. Alternate instructions for other operating systems (Macintosh) is also provided. The VM should automatically install on your computer.


  6. Determine how far away the main fetch area is from your beach.
    Determine the coordinates of your beach or a local buoy and calculate the distance from there to each of the "Highest Seas" positions recorded on the top half of your worksheet. Click here for the Stormsurf Distance Calculator (A virtual machine is not required, but you should have IE or Netscape 4.0 or higher). Otherwise, click here for an alternate distance calculator. Also copy the Date/Time and Max Sea Height data from the top half of the worksheet to the first two columns of the table on the bottom half of the worksheet (see example below). After you've calculated the distances (in nautical miles), record them into the appropriate column on the Swell Profile Worksheet like the sample below:

    Date/Time Max Sea Height
    (ft)
    Distance From Your Beach
    (nmiles)
    Max Potential Period
    (secs)
    Swell Arrival Time Estimate
      If Period =__ secs If Period =__ secs If Period =__ secs
    Swell Travel Time
    (Hrs)
    Swell Arrival
    Date/Time
    Swell Travel Time
    (Hrs)
    Swell Arrival
    Date/Time
    Swell Travel Time
    (Hrs)
    Swell Arrival
    Date/Time
    Wed AM 26 2153              
    Wed PM 31 1936              
    Thurs AM 36 1619              
    Thurs PM 33 1244              
    Fri AM 22 996              


    Helpful Hints:
    To determine the coordinates (latitude & longitude) of your beach, use a map, globe or use this link to NDBC to obtain very accurate coordinates for buoys that might be near your beach. Just select the buoy, and it's coordinates are near the top of the page.


    The alternate distance calculator link above requires a bit of practice to work with quickly, but once you get it wired, it's OK. Here's an example:
    Using the table in Step 2 above, let's say we want to calculate the distance from the storm position on Wed AM (Located at 45 degrees North and 175 degrees West) to our local buoy, say Buoy 46023 (Located at 34 degrees, 14 mins and 00 secs North, and 129 degrees, 58 min, 12 secs West). Remember, Latitude is North or South, Longitude is East or West.

  7. Enter the storms coordinates in the 'Source' column: 0450000N 1750000W
    (Note: Degrees must always be 3 digits, minutes and seconds 2 digits. Pad the coordinates with zeros as appropriate).

    Enter your position in the 'Destination' column (in this case, buoy 46023's coordinates): 0341400N 1295812W

    Hit the 'down arrow' button where it indicates "UNIT FOR RESULTS" and select 'Nautical Miles'.

    Hit 'Send Query' when your ready to calculate the distance.

    The result should be:
    "Distance between 45 0' 0"N 175 0' 0"W and 34 14' 0"N 129 58'12"W is 2152.4950 nautical miles".
    Enter "2153" nmiles in the table.

    Calculate the distance for the next storm position:
    To do this, hit the "Back" button on your browser. Notice your previous entries are still there. Enter the next set of storm coordinates and calculate the distance. See if your calculations are the same as ours. Repeat until you've calculated distances for all storm positions.



  8. Determine Maximum Swell Period and Record It
    Using the Swell Characteristics Table (below or from the worksheet), determine what the longest swell period that could result for each of the Max Swell Heights entries on your worksheet. A variety of conditions can converge to make the period slightly greater or less than what is indicated in the table. And remember, swells can travel at speeds/periods other than what is indicated below (like 12, 15, 16, 18 etc secs). These are just the units popularly reported at buoys.

    Swell Characteristics Table
    Max Confirmed Sea Height
    (ft)
    Max
    Potential Period
    (secs)
    Swell Speed
    (nmiles per hour)
    14-17 ft 11 sec 17.16
    18-24 ft 13 sec 20.28
    25-29 ft 14 sec 21.84
    30-34 ft 17 sec 26.52
    35-39 ft 20 sec 31.2
    40 ft + 25 sec 39


  9. Enter the Max Potential Period onto your worksheet like the sample below. Review the Max Potential Period entries you've made on the worksheet, taking the highest ones and entering them in descending order under the row 'Swell Arrival Time Estimate' (like below). Remember, longer period swells move faster than shorter period swells, so it is most likely the longer period swells will have the shortest travel time, and therefore arrive first.

    Date/Time Max Sea Height
    (ft)
    Distance From Your Beach
    (nmiles)
    Max Potential Period
    (secs)
    Swell Arrival Time Estimate
      If Period = 20 secs If Period = 17secs If Period = 14 secs
    Swell Travel Time
    (Hrs)
    Swell Arrival
    Date/Time
    Swell Travel Time
    (Hrs)
    Swell Arrival
    Date/Time
    Swell Travel Time
    (Hrs)
    Swell Arrival
    Date/Time
    Wed AM 26 2153 14            
    Wed PM 31 1936 17            
    Thurs AM 36 1619 20            
    Thurs PM 33 1244 17            
    Fri AM 22 996 13            

     

  10. Determine Swell Arrival Time
    Start with the most energetic swells (the fastest moving ones). For the row or rows with the highest period, divide 'Distance From Your Beach' by 'Swell Speed' (from the Swell Characteristics Column) to obtain swell 'Swell Travel Time'. Record 'Swell Travel Time' on the worksheet in the appropriate column. Then figure Swell Arrival Date/Time.

    For example: For the swells generated on Thurs AM, the max potential period for those swells is 20 secs. These swells are clearly most likely to be the most energetic and therefore fastest moving. Divide the distance the storm was away from your beach on Thurs AM (1619 nmiles) by the swell speed for 20 secs (31.2 nmiles per hour). 1619 nmiles divided by 31.2 nmiles per hour equals 51.89 hours. In short, the swells generated on Thurs AM will take 52 hours to reach your beach! Also determine the swell arrival time. 52 hours is equal to 2 days 4 hours (24 hours in a day, right?) So the swells generated Thurs AM will arrive Saturday AM plus 4 hrs!


    Date/Time Max Sea Height
    (ft)
    Distance From Your Beach
    (nmiles)
    Max Potential Period
    (secs)
    Swell Arrival Time Estimate
      If Period = 20 secs If Period = 17 secs If Period = 14 secs
    Swell Travel Time
    (Hrs)
    Swell Arrival
    Date/Time
    Swell Travel Time
    (Hrs)
    Swell Arrival
    Date/Time
    Swell Travel Time
    (Hrs)
    Swell Arrival
    Date/Time
    Wed AM 26 2153 14            
    Wed PM 31 1936 17            
    Thurs AM 36 1619 20 52 hrs Sat AM
    + 4 hrs
           
    Thurs PM 33 1244 17            
    Fri AM 22 996 13            


  11. Compute the swell arrival times for all other reasonably significant swells generated from this storm (in this case, anything with a period of 14 secs or greater). Also remember that on Thurs AM not only were swells of 20 secs generated, but also ones of 17 and 14 secs. Compute all those arrival times. (Hey, it's only simple division! Get a cheap calculator for 5 bucks at KMart). Your table should now look like this:

    Date/Time Max Sea Height
    (ft)
    Distance From Your Beach
    (nmiles)
    Max Potential Period
    (secs)
    Swell Arrival Time Estimate
      If Period = 20 secs If Period = 17 secs If Period = 14 secs
    Swell Travel Time
    (Hrs)
    Swell Arrival
    Date/Time
    Swell Travel Time
    (Hrs)
    Swell Arrival
    Date/Time
    Swell Travel Time
    (Hrs)
    Swell Arrival
    Date/Time
    Wed AM 26 2153 14         99 hrs Sun AM
    + 3 hrs
    Wed PM 31 1936 17     73 hrs Sat PM
    + 1 hr
    89 hrs Sun AM
    + 5 hrs
    Thurs AM 36 1619 20 52 hrs Sat AM
    + 4 hrs
    61 hrs Sat PM
    + 1 hr
    74 hrs Sun AM
    + 2 hrs
    Thurs PM 33 1244 17     47 hrs Sat AM
    + 11 hrs
    57 hrs Sat PM
    + 9 hrs
    Fri AM 22 996 13            

     

  12. Analyze Results
    So by reviewing the completed worksheet (or the Swell Arrival Time results window from the Calculator), it looks like the first part of the swell will hit on Saturday AM plus 4 hours with a period of 20 secs (just barely). It also looks like the swell will fill in and transition to 17 secs on Sat PM plus 1 hour. This will probably be the biggest and most consistent part of the swell since the storm generated seas in the 17 sec range for 24 hours and it's all hitting our beach at close to the same time. But even by Sunday AM, at first light, some energy will still be present to 17 secs before transitioning to 14 secs by Sun AM plus 2 hours and starting to fade. Even though we didn't calculate it (because we ran out of columns on the worksheet), swells of 13 and 11 secs will be arriving after Sunday PM. In fact, the 11 sec swells generated on Wed PM will hit 112 hours later, or Monday AM plus 4 hours, though of much diminished size due to their lesser energy level and associated decay.

    But, assuming the data for Thurs AM, PM and Fri AM was based solely on forecast storm positions and swell heights from the wave model, it would therefore be highly suspect (because it is not "confirmed" data). The only valid swell forecast is one based on actual '00hr' confirmed readings. Once the '00hr' data becomes available, it is suggested that you recompute the swell arrival time estimates for Thurs AM, PM and Fri AM (if they are much different from the forecast sea positions and heights) to get a more realistic assessment of how this swell will develop.


  13. Putting it all Together
    The real trick to pulling together a detailed forecast and scoring good waves is knowing how to read the worksheet (or the results windows from the Calculator) once it's all filled out. It takes some practice and thought, but the results will put you way ahead of the crowd.

    To tune your forecasts even better, develop tables that map how long it takes a swell to migrate from your outer buoys to your beach (assuming you have buoys to work with). Tables for North and Central California are provided below. The Swell Characteristics Table should help you estimate swell speeds, and the NDBC website and a map should help you estimate the distance from buoys to your beach. With some practice, you should be able to predict when a swell will hit to within an hour or two.

    Use local high-resolution atmospheric models (MM-5, MAPS, ETA) to determine what the local winds will be when the swell hits. Adding your understanding of local winds, tides and swell direction to the forecast, you're sure to know which breaks will be firing when the big one arrives!

  14. Using Outer Buoys to Fine Tune the Arrival Times of Swells in North and Central California

North Pacific Swells

South Pacific Swells

For the truly hardcore, here's a paper that translates buoy readings into actual wave height measurements and proposes standards for rating and categorizing swells. Enjoy!!

29745

.
Contact | About | Disclaimer | Privacy | Advertise/Content | Links
Copyright 2014 STORMSURF - All Rights Reserved
This page cannot be duplicated, reused or framed in another window without express written permission. But links are always welcome.

Buoys | Buoy Forecast | Models | Pacific Forecast | QuikCAST | Chartroom | El Nino | Tutorials | Reports | Great Circles | Calculator | News