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  1. #1
    Join Date
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    Micah, question on tide heights, etc...

    Micah is there a reason why on the west coast tide heights are given ie:4.3 while they are not given on the east coast...whenever you see a westcoast surf report the heights are given while on the east coast they arent...am i wrong?

    or shall i say maybe given, but more talked about on the west coast...

    and another question why on the west coast do they always emphasize swell direction in degrees while that is not talked about here on the east coast?

    thanks
    Last edited by Beef; Oct 18, 2007 at 03:42 AM.

  2. #2
    Join Date
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    good questions...

    First off the tides:
    Yes, the actual height of the high and low tides is a big factor... and does influence the east coast surf as well. However, these changes in tidal heights dont seem to be as influencial on the east coast. The major difference here is that the west coast is dealing with generally much long period swells. The longer the period swell, the more influence the water depths will influence the refraction/defraction and shoaling processes.

    As for the emphasis on swell direction:
    In Southern California, especially this is important, because of the wave shadowing due to point conception (to the north) and the offshore islands. So, a couple degree change can make or break a particular area as the swell will either be blocked or pass through the southern california bight region. This setup, makes SoCal one of the most challenging areas in the world to forecast for.

    Having said that, the precise degree of the swell is important everwhere, but particularly when you are talking about steep angled swells ! So, in Delaware, many beaches face pretty much due East. So, as a generalized statement, lets say Delaware receives anything from due N to due S swells. But, if there is a little bit of W during a wind swell event, then it makes a big difference. So, a swell from 180 degrees will be bigger than the same size swell from 185 degrees and so on. Swell refraction is a big factor with these type of steep angled swells, and is one of the hardest things to forecast. The refraction process varies from break to break, and understanding this generally requires intimate knowledge of particular spots.

    The Swellinfo detail forecasts, describe swells with regards to the text direction (S, N, E), but to look at the actual direction in degrees, click on surf plot (view details) or the swell plots.

    Swell Plots for South Orange County (offshore swells).



    Make Sense?
    Last edited by Swellinfo; Oct 18, 2007 at 09:14 AM.

  3. #3
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    yes makes great sense...in terms of the height, i have a general idea, but what is the exactly the height...meaning from what point to what point is the height they are talking of? From a certain point of the water to another point?

  4. #4
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    from the trough of the swell to the crest

  5. #5
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    Beaner, i believe he was asking about the tidal heights.

    For tidal heights, we use a standard based on a term called Mean Lower Low Water (MLLW). So, this is a mean value of the water height at a particular location during low tide. Any variation from this level is + or 1 that MLLW value.

    So, when we say +3.5ft, this means 3.5 feet above mean lower low water. Thats why, the low tides dont generally go very far below zero.

  6. #6
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    so how do they determine where to make the mark to measure?

  7. #7
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    they have tidal stations that take constant measurements. So, each station will have a mean lower low water value, and variations are taken from there. I believe from the data provided at these stations, empirical equations have been developed which take into account sun and moon gravitational forces along with other variables. These equations would then allow for predictions in many places of the world. I'm not familiar at all with these equations, but it is certainly interesting.

  8. #8
    Quote Originally Posted by Beef View Post
    so how do they determine where to make the mark to measure?
    I am sure I am wrong but my gut guess would be Sea Level.

  9. #9
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    Quote Originally Posted by Beef View Post
    so how do they determine where to make the mark to measure?
    Look at it this way. Think about the piles that hold up a pier. At low tide every day for a year you mark on a pile the lowest point that the water hits. These marks will have a range of say a few feet depending mostly on the position of the moon. You then take the average of all these marks, which would fall somewhere in the middle of all the marks, and this is level from which low and high tide are measured.

  10. #10
    The tide charts i print out for delmarva coast gives the tide heights. Always have. lot of difference between a 3.5' high tide and a 5' high tide in terms of how likely it will be mushy at certain spots.

    I usually use the Fenwick Island Ocean location figure its representative of the whole delamarva ocean coast.

    http://tbone.biol.sc.edu/tide/tidesh...+Light&units=f
    You can mess around with the page format and get it to print an entire month on one page by clicking the one month calendar type output.
    Last edited by South Bethany; Oct 18, 2007 at 04:30 PM. Reason: tide chart link