# SI wave height scale

Discussion in 'All Discussions' started by mattybrews, Nov 25, 2014.

1. ### mattybrewsWell-Known Member

Apr 14, 2013
Looked all over the site and forums for this before posting and couldn't find anything. What scale does SI use when they give their wave height predictions? Is it face height or measured from the back? I know it can't be 100% accurate, but for a few spots out here it seems like going by face height it's consistently a foot or two bigger than the forecast. And the forecast is pretty reliable.

Aug 21, 2012
#Belmarscale

3. ### nynjWell-Known Member

Jul 27, 2012
0'-22' - FLAT
23' - Firing
24'+ - impossible

4. ### sisurfdoggWell-Known Member

Jun 17, 2013
I always go surfing with my entire quiver: 9' Gun, 7'2" semi-gun, 6'8" step up, 6'2" hbsb, 9'2" hplb, 9'6"noserider, 5'6" groveller, 6' fish, 6'4"rocket fish, kayak, jet ski, 12' douchecanoe, and a pair of swim fins and a handplane. You just never know what the waves will be like when you get there.

5. ### titsandpitsWell-Known Member

Sep 4, 2012
the face in Nj at least

6. ### MitchellWell-Known Member

Jan 5, 2009
Do you really take note of a bunch of wave heights for a few minutes and then compute the average.

I'm not trying to be sarcastic, I just suspect many wave height forecasts are based on the output from models that predict average wave heights, or dominant wave heights which might be like the 65th percentile average of all waves coming in.

I think a lot of surfers stand on the beach for 10 minutes, look at mostly the set waves that they would be interested in riding and not all of the in-between waves and then conclude that its 4-6 foot (for example) when TONS of 2-3 foot waves also come in, bringing the average height down to say 2-4 foot and then conclude that the forecast is an undercall because SOME 4-6 foot waves are coming in. Also we tend to look at the "peak" section of the wave which is higher than the shoulders.

Just my 2 cents.

Also, there are spots that consistently just exceed the surrounding beaches and probably aren't representative of the forecast for a "zone" of coast.

Last edited: Nov 25, 2014
7. ### EmassSpicoliWell-Known Member

Apr 16, 2013
They base it off the 8-10' principle.

8. ### CDsurfWell-Known Member

May 10, 2014
they must have measure the faces today because there is no way it was head high where I surfed. Waist to chest high at most.

9. ### daeggmanWell-Known Member

Sep 18, 2014
lol actually laughed out loud

10. ### NJ glideWell-Known Member

Jun 8, 2013
They measure it with my 23ft Johnson in Belmar while I bench.

11. ### ibcWell-Known Member

Aug 3, 2014
Don't fergit that SUP witha stripper pole. Git-R-Done

12. ### spikeb122Well-Known Member

Jan 13, 2009
interestingly enough, the significant wave height is the average of the top 1/3 of waves. it is a convention that was first adopted when asking people how big they thought the waves were they often gave this number of the top 1/3 of wave heights. from a statistical standpoing it's 4 times the standard deviation of the surface elevation. ... there's plenty more but then you start getting into oceanography

to answer the original question... it's face height. and you should feel lucky that it's consitantly bigger than the forecast.. not everyone's so lucky. also the models aren't as accurate in some places as others. to improve the model there's the + 0 - scale next to the graph of forecasted wave heights . .. this provides feedback for the modelers to let them know when they've under/over predicted the swell events. with out this feed back how is a guy in delaware going to know the wave heights in oregon are under predicted on this or that swell

13. ### mattybrewsWell-Known Member

Apr 14, 2013
You are probably right. If you're sitting way outside waiting for the big sets you tend not to notice all of the smaller sets breaking inside. If that's the case then it's pretty spot on most of the time going by face height.

There used to be a scale... But, if you look at the forecast, you will notice it offers a text descsription (ie. head high), and also a wave height in feet (4-5ft), so I'm not sure a scale is necessary at this point, since its pretty explicit.

15. ### CDsurfWell-Known Member

May 10, 2014
SI kicks butt though, they are usually pretty spot on

16. ### Mr.BelmarWell-Known Member

Aug 19, 2010
I actually rather the forecast be undercalled... Then when you do get those 5 ft days that are perfect and uncrowded, you can thank swellinfo.com for calling it 2-3ft

Unless, that is, you head straight to Belmar,NJ where the waves are always at least double the size of the surrounding towns... Just because it's Belmar

17. ### Mr.BelmarWell-Known Member

Aug 19, 2010
I agree, usually the text description is spot on...

18. ### SandblastersWell-Known Member

May 4, 2013
hey bro can i buy the 12' douchecanoe and the ski i want to do tow in one 2 foot days?

19. ### worseyWell-Known Member

Oct 13, 2013
shaq and tattoo are still arguing about it.

20. ### Riley Martin's Disgruntled NeighborWell-Known Member

Aug 22, 2012
For what its worth, nynj, you are my favorite.