Click for JetForums Click for Nordhavn Click for Northern Lights Click for YF Listing Service Click for Mag Bay

Deciphering ocean condition forecasts

Discussion in 'General Yachting Discussion' started by bluestar, Apr 3, 2012.

You need to be registered and signed in to view this content.
  1. bluestar

    bluestar New Member

    Joined:
    Feb 9, 2012
    Messages:
    15
    Location:
    Alameda, CA
    Hello, below is a typical NOAA ocean condition forecast. Can you help me decipher what it is saying? The only part I can be sure is the winds part:

    SW WINDS 10 KT. WIND WAVES 2 FT OR LESS. NW SWELL 9 TO
    12 FT AT 13 SECONDS AND S 3 FT AT 15 SECONDS.

    Specifically, I'm wondering:

    What is a "wind wave"?
    What is a "swell"?
    What are all those "seconds" about?
    What data is more crucial to boating in the sea?
  2. AMG

    AMG YF Moderator

    Joined:
    Jul 26, 2004
    Messages:
    5,378
    Location:
    Sweden
    Are you serious..?
  3. AlfredZ

    AlfredZ Senior Member

    Joined:
    Oct 29, 2009
    Messages:
    562
    Location:
    Landlocked in Europe
    Hi there,

    Wind waves are waves generated by winds, swells are waves generated by surface gravitythe seconds are the wave period for swells which is the travel time of the wave group. You have to know all those information so you know what will be slapping your boat harder and from which direction so you can plot the best routes and choose the headings that will be best for your boat, safe and faster to reach your intended destination.

    Cheers,
    Alfred
  4. bluestar

    bluestar New Member

    Joined:
    Feb 9, 2012
    Messages:
    15
    Location:
    Alameda, CA
    Absolutely! If you can help that'll be great. Thanks in advance.
  5. Marmot

    Marmot Senior Member

    Joined:
    May 20, 2007
    Messages:
    3,311
    Location:
    9114 S. Central Ave
    Nobody is born knowing that stuff ...

    Download and print this booklet:

    http://www.vos.noaa.gov/ObsHB-508/ObservingHandbook1_2010_508_compliant.pdf

    It has way more then you really need right now and is aimed at the mates on a deep sea ship who provide weather data but the explanations are very clear and easy to understand (they are written for deckies so they have to be simple) and if you take the time to wade through, all your questions will be answered very well.
  6. saltysenior

    saltysenior Senior Member

    Joined:
    Aug 22, 2009
    Messages:
    289
    Location:
    stuart,fl.
    AND S 3 FT AT 15 SECONDS.

    never understood that part of the forecast...
  7. C4ENG

    C4ENG Senior Member

    Joined:
    May 19, 2006
    Messages:
    581
    Location:
    Ft Lauderdale
    I did not exactly understand that either:
    WIND WAVES 2 FT OR LESS. NW SWELL 9 TO 12 FT.
    What would I expect to see exactly? 2 ft wind waves on top of 12 ft swells?
    I think I just might read Marmots link to figure it out as well.
  8. vivariva

    vivariva Senior Member

    Joined:
    Dec 10, 2007
    Messages:
    187
    Location:
    Istanbul, Turkey
    Aren't the seconds the swell interval, thus increase in height will increase the interim period between the one wave and the next?

    It is a mixture of waves generated by different weather at different locations I believe.
  9. Marmot

    Marmot Senior Member

    Joined:
    May 20, 2007
    Messages:
    3,311
    Location:
    9114 S. Central Ave
    Why not just RTFM?
  10. saltysenior

    saltysenior Senior Member

    Joined:
    Aug 22, 2009
    Messages:
    289
    Location:
    stuart,fl.
    the FM will not download
  11. Kevin

    Kevin YF Moderator

    Joined:
    Nov 25, 2004
    Messages:
    3,050
    Location:
    Montreal, Qc, Canada
    It just worked for me.
  12. AlfredZ

    AlfredZ Senior Member

    Joined:
    Oct 29, 2009
    Messages:
    562
    Location:
    Landlocked in Europe
    If right-click, save target on the link did not work for you, PM me your email and am more than glad to send it to you.

    Cheers,

    Alfred
  13. saltysenior

    saltysenior Senior Member

    Joined:
    Aug 22, 2009
    Messages:
    289
    Location:
    stuart,fl.
    finally got it ,but i'll never live long enough to read it all and too old to understand it........

    so i'll just ask.....how can a 3 ft. S.[waves] be 15 seconds apart ??? I know if I was hanging on to the local bell buoy for dear life, I would be hit in the face faster than every 15 secs..:confused:
  14. triggerfish23

    triggerfish23 Member

    Joined:
    Jan 19, 2012
    Messages:
    43
    Location:
    Seattle, WA
    This is the second set of swells. The wind waves don't have a timing listed, but both sets of swells do.

    You're right, you'd probably rather not be hanging on to a buoy (probably no matter the conditions)http://www.yachtforums.com/forums/images/icons/icon10.gif
  15. AlfredZ

    AlfredZ Senior Member

    Joined:
    Oct 29, 2009
    Messages:
    562
    Location:
    Landlocked in Europe
    Good thing you got the PDF.

    The speed of a wave set in a swell is three times its period in seconds, so if the period is 15 seconds then the wave speed is 45 knots per hour, which is you might notice now is a big wave set, sets at such size of height, period and speed does not lose energy energy. By this information you can judge the nature of the swells and how frequent they will effect your boyant motion. Surfers take swell information of deep sea into regard because they can tell when the big surf will be coming to shore and what heights and lengths to expect.

    Cheers,

    Alfred
  16. bluestar

    bluestar New Member

    Joined:
    Feb 9, 2012
    Messages:
    15
    Location:
    Alameda, CA
    So let me take a crack at deciphering the original example; please correct me if I'm wrong:

    SW WINDS 10 KT. WIND WAVES 2 FT OR LESS. NW SWELL 9 TO
    12 FT AT 13 SECONDS AND S 3 FT AT 15 SECONDS.

    1) SW WINDS 10 KT. = Winds of 10 knots blowing from Southwest direction.
    2) WIND WAVES 2 FT OR LESS. = There is 2' waves caused by the wind on top of 9-12' swells
    3) NW SWELL 9 TO 12 FT AT 13 SECONDS = 9-12' swells are traveling from northwest to southeast at a speed of 39 knots.

    I still cannot figure out what this is:

    4) S 3 FT AT 15 SECONDS
  17. AlfredZ

    AlfredZ Senior Member

    Joined:
    Oct 29, 2009
    Messages:
    562
    Location:
    Landlocked in Europe
    Correct. The other, is just another swell group coming at you from south, being three ft high at a rate of 45 knots. One more piece of info is that the seconds also tell you how long is it between the highest waves in each set, so it is 15 seconds between the highest wave in set-1 and set-2, etc. (You can have many sets in many directions)

    Cheers,

    Alfred.
  18. saltysenior

    saltysenior Senior Member

    Joined:
    Aug 22, 2009
    Messages:
    289
    Location:
    stuart,fl.
    have not a clue to what you are saying,,,,however i'm glad i'm not in that part of the ocean............sounds like what we use to call ''hobble-gobble''