Swell height vs. wave height

Discussion in 'Weather and Surf Forecasting' started by clintopher, Aug 12, 2012.

1. clintopherWell-Known Member

Jul 12, 2011
What's the difference between the two on the buoy data? Since I've been looking at the buoys, which isn't very long, I've noticed that the wave data is always larger with a shorter period. So my guess is the wave data is local wind driven conditions and the swell data is the ground swell from wherever. Is that right?

How does it translate to beach conditions? Obviously each beach is different but are there any rules of thumb?

2. MitchellWell-Known Member

Jan 5, 2009
The amount of swell showing on the buoy (swell height and period) is more useful than the total wave data, (mean wave height and period) which includes all wave data in the mix, including (when its windy) the locally wind generated chop heading sideshore and offshore that generally show on the beach.

mean wave height and period = 6 feet at 6 seconds
swell height and period = 2 feet at 8 seconds

I'd be expecting that 2' @ 8 seconds to be more like what you'll see for surf.

Last edited: Aug 12, 2012

May 19, 2006
The significant wave is roughly the wave height of the top 30 percent of all waves.
The swell height on the buoy maps refers to the primary swell at the buoy location.

With statistical approaches we can segregate wave magnitude, frequency, and direction at the buoy location into individual swell groups.

Both significant wave height and primary swell height are telling in the breaking wave. As are secondary and tertiary swells. This intricate nature of the wave spectrum is one of the trickiest part of forecasting. You have to think of waves in terms of an entire 360 degree spectrum.

Primary swell is usually the most telling, but additional swells can combine to become additive to the total breaking wave height.

Some examples:
Significant wave height: 5ft
Primary swell: 3ft @ 12 seconds, ESE
Secondary swell: 5ft @ 6 seconds, NW

If this is an east facing break, the secondary swell is actually moving away from the coast, do the primary swell will be most telling.

Significant wave height: 5ft
Primary swell: 3ft @ 12 seconds, ESE
Secondary swell: 4ft @ 9 seconds, SSE

In this example the primary and secondary swells are additive to create a bigger overall significant wave height.

woof likes this.
4. shark-hunterWell-Known Member

Apr 29, 2012
That's not totally accurate in all cases. We are on the east coast. Unless you're talking about strong nor'easters, hurricanes most of the swell generated is very localized so significant wave height is more important than the swell measurement on the buoy.

For example, right now here the swell height is "(.)7 feet" at 11 seconds and the significant wave height is 6 feet at 8 seconds out of the sw. It's waist to chest right now. Not less than 1 foot. Just pay attention to the direction of the swell. Significant wave height is more important than swell height here on the east coast ESPECIALLY in summer with fronts creating most of the wave action.

I must add, If there's a signifcant medium period/ ground swell in the water than swell date on the buoy is your go to measurement!

Last edited: Aug 12, 2012
5. MitchellWell-Known Member

Jan 5, 2009
I was just talking about sideshore/outgoing locally generated wind wave height not really mattering

I agree that if the local wind waves coming onshore, then they add to the surf height.

6. shark-hunterWell-Known Member

Apr 29, 2012
Oh ok. Yeah a great example would be A south swell 3 feet at 7 seconds and a nw swell 3 feet at 7 seconds. The buoy would show significant wave height 6 feet at 7 seconds. Of course we all know that's completely misleading for surfers, but very useful for mariners.

7. jsimmojNew Member

Oct 13, 2016
is 6ft waves at 8 seconds good conditions?

Mar 6, 2016
Mason Leeser

9. seldom seenWell-Known Member

Aug 21, 2012
#WWMLD
#MasonLessreAntilles

#clintopher

10. kidde rocqueWell-Known Member

Mar 6, 2016
Haha, next level sh!t right there. Can't believe it was sitting in front of me this entire time lol

#clitofher

Jul 27, 2012
a

12. seldom seenWell-Known Member

Aug 21, 2012
Ahhh Kidde as much as I wish I could claim that, I must give due credit to Valhallalla, as teh phrase was birthed in his witty brain. What a great think tank, you guys are the best.

Mar 6, 2016

14. ZeroevolWell-Known Member

Jun 22, 2009
You jerks get me every time with these threades pulled up from 6 years ago! lol

Yankkee likes this.

Mar 10, 2013

16. sixfootrideMember

Aug 3, 2016
Try dropping in. Wahoo Style. Straight to the beach. Cutting it way late. Stall while digging deep. Plain covered slow. Height adjusts dramatically.

Sep 12, 2017