# Thread: Micah - "multiple" vs. "single" swells

#### Hybrid View

1. Senior Member
Join Date
Jan 2007
Posts
412

## Micah - "multiple" vs. "single" swells

micah,

I've wondered for a while whether "individual" swells of different periods but from roughly the same direction are additive? For example on sunday 8 a.m. for OCMD your swell plot shows 1.3 @ 9 ESE and 3.0 @ 6 S. so adds up to 4.3 feet but your surf forecast is knee-occ. waist

Monday 8 a.m. is 4.3 @ 7 S. surf forecast is waist - chest.

if the two swells sunday were diff periods but same direction...would that change things?

Aren't even "individual" swells like the monday 4.3 @ 7 from S. still an average (maybe concentration is a better word) of a spectrum of periods and directions anyway?

Sorry to throw yet another stupid question your way

2. hi good question. the simple answer, is NO, swells are not cumulative.

So, when the swell plots show 1.3 @ 9 ESE and 3.0 @ 6 S, then this doesn't mean there is going to be a 4.3ft wave in the water. Essentially, you will see both swells when you are in the water. Some of the energy will be from the ESE direction, and some from the S direction.

The swellinfo text surf forecast will describe the dominant swell, which in this case is the 3.0ft @ 6secs, which the forecast called for knee to waist high waves. Take note of the entire text forecast:

Knee to waist high SSE short period wind swell.

Knee to waist high describes the height, SSE the direction, and short period wind swell explains the swell period. And so, you can see that this forecast is describing the 3.0ft @ 6seconds from the S. Another thing that is not so obvious, is the Surf Plots are color coded by the dominant swell. So, if you click on the "view details", you can match the color of the surf timeline to the dominant swell data.

So, that was the simple answer. In near shore surf zone physics, there can be wave to wave interactions, but this is not a simple cumulative effect and can be ignored for a generalized regional surf forecast.