Windstorm play adds a whole new dimension to Mahjong. Instead of just matching tiles that are free to slide left or right, in Windstorm, tiles are matched according to the prevailing wind. The current direction is shown by the compass below

If the prevailing wind is East-West, tiles can only be matched the regular way: those that can slide right or left.

If the prevailing wind is North-South, tiles can only be matched when they can slide up or down. A whole new strategy for winning the game must be employed when the winds change.

However when all four points of the compass light up there's a windstorm! Tiles that can slide either left, right, up or down can now be matched with each other.