When NOT to apply Buy Ballots Law
Near the equator:
Buys Ballot’s law should not be applied within a few degrees of the equator. This is because Coriolis force is negligible at the equator and therefore the winds blow directly across the isobars from HP to LP areas.
In the vicinity of land:
This is because the wind experienced may not be the free unobstructed wind. It may be wind deflected by the land.
Ref : Marine Meteorology by Capt. H Subramaniam