[Paddlewise] Veering Winds

From: "Doug Lloyd" Subject: Re: [Paddlewise] Soft Water (was?)


>
> The other thing that can catch newer paddlers intent on a little fun and
> adventure in rough seas is sudden wind direction change. The transition
> time can be very short when a front moves through rapidly, and if you
> haven't allowed enough of a margin or if the wind direction is integral
> to reaching shore you could be in for a bit a beating - or worse.
>

hi,

a couple of years ago, i read the scientific literature that compared (a)
observations of the rate at which seas adjust to veering winds and (b)
numerical model predications.

the numerical models relied  heavily on a factor that accounts for the
strength of wave-wave interactions. that factor is difficult to measure
directly, but by heavy numeric Klass Hasselman of Germany obtained a
solution from some nasty equations. Hasselman is famous worldwide for that
pioneering work.

However, the computations were done for wave-wave interactions with waves
traveling in one directions. During veering winds, the wind direction
changes and there are waves from various directions.

It happens that the numerical computations *do not* agree well with
observations of waves during veering wind conditions. The wave field changes
about twice as fast as is predicted by the models.

Thus Doug's comment that the transition time can be very short when a front
moves rapidly agrees with what i read.....

the modeling problem may have been addressed during the past few years, but
it is still prudent to be aware that fronts and veering winds make life very
difficult folks who are paid to make wave forecasts.


bye bye bliven



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