If the seasonal winds outright reverse, I guess other factors like where other currents "push" water will start to matter. That is bound to modify a starter set of wind-driven current guesses anyway. Or decide one season has stronger winds than the other, and just say the total winds up being a weak current in the slightly predominant direction. Or if you're not talking whole oceans worth of water sloshing around, let the current reverse with the winds... would make for some interesting commerce possibility :-).