It's a neat tool and not one I'd seen before - thanks!
Is decent wind prediction 24 hours in advance or even 12 hours in advance immpossible?
Pretty much. The note at the bottom of their pages says "Our forecast charts are derived from the GFS and WaveWatch III weather models, the same weather models that produce the GRIB files used by modern electronic navigation software and weather routing software."
The biggest issue is that none of these models take into account local
weather alteration caused by actual
cloud cover, topography (mountains, hills, valleys, ..trees!) changing wind direction and strength or by man-made alterations to the surrounding landscape (eg. large suburban areas cause localised ground heating, hence thermals, hence localised barometric pressure changes) changing wind strength (and direction to a smaller extent) for miles around.
The best use of these models is to tell you when the local situation might change, but the most accurate forecast you'll get will be the one you make yourself by looking out of the companion-way first thing in the morning.