"Not Credible"

Then Moses raised his hand over the sea, and the LORD opened up a path through the water with a strong east wind.  The wind blew all that night, turning the seabed into dry land.  So the people of Israel walked through the middle of the sea on dry ground, with walls of water on each side!  [Exodus 14.21-22]
In just a moment of pondering, I find this account quite incredible - as in "not credible".  I've tried to consider how this could have taken place by natural means, but there is no expalanation.  If the parting of the Red Sea was all the result of a fierce east wind, that would at least start to make some sense...  But then I find a real problem understanding how people could have walked (not to mention stood up) in the velocity of wind it would have required to part the waters.
So, once again in my journey of life and faith, I find myself at a crossroads of decision: Do I require a natural explanation of everything, or do I simply (and against natural understanding) believe?
Father, You know my heart and my head.  Like Thomas of Jesus' men, I find myself needing some proof.  Help me though to be like those who believed without seeing.