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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:
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.
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 |
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'.
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'.
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.
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.
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 |
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 |
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 |
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 |
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!!
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