Waves and Currents


  • Sailor

    Are your wave models taking into account surface currents? I am about to sail a 47ft sloop from La Reunion to Cape Town and a serious consideration is the Agulhas current running down the East coast of South Africa from ~NNE to SSW. This reaches up to 2.5-3 knots and is reputed to exacerbate (severely) the steepness and height of the waves when the wind is contrary (S - WSW). Are any of your models taking this into account and, if so, which is going best to show this?

    Thanks for continuing to do an amazing job!

    In passing, any chance you might do an app which can pickup server data sent by email over a satellite phone? Windy is great, but the bandwidth required is huge and impractical to pick up offshore.


  • Sailor

    @afurley
    All waves models don’t take into account the effect of current.

    For WAM model from ECMWF(July 2018):
    « Considerations when using output from ECWAM
    Not yet modelled are the interaction of waves with sea-surface currents. In particular areas, (e.g. Gulf Stream or Agulhas current), the current effect may give rise to localised changes of up to a metre in the wave height »
    From
    https://confluence.ecmwf.int/plugins/servlet/mobile?contentId=131397261#content/view/131397261

    For WWW3 model it seems to be different (March 2019):
    https://github.com/NOAA-EMC/WW3/wiki/Manual
    Page 1
    « The model [....] computes other transformation processes such as the effects of surface currents to wind and wave fields, and sub-grid blocking due to unresolved islands »
    Page 163
    « 3.9 Winds and currents
    Model input mainly consists of wind and current fields. Within the model, winds and currents are updated at every time step ∆tg and represent values at the end of the time step considered. »

    In any case it would be much better for you to sail downwind and down swell. But this is quite tricky in the Agulhas current area, the swell being mostly from SW. Don’t you plan a stop in Durban?

    Concerning receiving data via satellite phone:
    https://community.windy.com/topic/6601/offline-use-of-windy



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