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 Chas. 02-17-2013 06:46 PM

Determining storm distance by wave freq. or ampl.

Hi, All,

I think that years ago I heard there was a rule of thumb for estimating the distance of a storm by measuring the wave frequency or amplitude. Does anyone know something about this? Thanks.

 Bene505 02-18-2013 07:29 PM

Re: Determining storm distance by wave freq. or ampl.

Also, I know someone that is doing some research on wase (face) height versus swell height.

Regards,

 nolatom 02-18-2013 07:37 PM

Re: Determining storm distance by wave freq. or ampl.

I don't know but it sounds interesting.

As a rule, I use my thumb to find NWS on my iphone or VHF, then measure from what they say ;-)

 casey1999 03-19-2013 09:43 PM

Re: Determining storm distance by wave freq. or ampl.

 casey1999 03-19-2013 09:51 PM

Re: Determining storm distance by wave freq. or ampl.

Here in Hawaii, if a wave train has periods in the teens of seconds say 13-17 seconds, those waves are generated by storms at least 2-3,000 miles away. Short period waves under 10 seconds are generated by winds within say 800 miles.

the long period waves (13-17 seconds) can have wave heights up to 30 feet or more. That will lead to a breaking wave face of 60 feet or more. The longer the wave period the more energy for equivilent height ocean swell.

 geronimotwo 03-20-2013 12:21 PM

Re: Determining storm distance by wave freq. or ampl.

wouldn't wind speed, and the change of wind speed have greater effects on frequency of the waves than the distance of the storm?

 casey1999 03-20-2013 02:26 PM

Re: Determining storm distance by wave freq. or ampl.

Quote:
 Originally Posted by geronimotwo (Post 1005198) wouldn't wind speed, and the change of wind speed have greater effects on frequency of the waves than the distance of the storm?
I did not completely read the article, and do not fully understand what I did read. But my understanding is wind speed, fetch, and time determine wave height. As your distance from the winds that generated the waves increase, the wave height decreases. Also, waves travel in the direction of the wind that generated them. You could be 500 miles from a storm, but a location 3,000 miles away may get larger waves if that is the direction the waves are moving. The frequency of the waves gets lower (longer wave length) as you move farther away from the storm. The acticle says somthing to the effect the lower frequency (longest wave length) waves travel faster and arrive first at a location, then the shorter wave length waves arrive.

Here is a good site to see how this all works:
Sailing Weather - Marine Weather Forecasts for Sailors and Adventurers - PassageWeather

Compare the maps that show wave height and direction to the maps that show wind speed and direction. Note these maps do not show wave frequency (wave length) but you can bring up bouy data that does give that information. For the same height wave, the wave with longest wave length (lowest frequency) has the more energy and will break with a higher height once it reaches shore. This can be seen in a tidal wave. At sea, a tidal wave may only be 6 inches high (and moving at 500 miles per hour), but its wave length is measured in miles, and when it hits land, it generates huge amounts of energy. Although a tidal wave is not generated by wind, the physics of the wave model are the same.

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