Someone walking on the water would be
"supernatural" - full stop - unless there was some
"natural" explanation.
We all know, from experience, that men don't walk on water, unless there's some sleight of hand going on. Some time ago there was a magic show on TV, and some well known magician seemed to be walking on the River Thames. I noticed though that he seemed to be very careful where he was putting his feet, and the alleged cop boat that "rescued" him didn't make too many waves getting to the pick up point. Also the sides of his shoes seemed to be slightly submerged.
I'm pretty sure he had a perspex platform anchored just below the surface of the water, and he didn't want to fall off the (hard to see, even from his position) sides, nor did he want the boat ploughing into his (probably expensive) trick.
But Christ walking on the water in a storm would have been of a completely different order, and if we'd been there, the first thing we'd
know to the core of our being is that something supernatural was going on, in the full sense of the word.
Also these "hypotheticals" are so dry and wan - if someone came walking across the water to us in the middle of a storm, the last thing we'd be playing around with would be dry intellectual questions. We'd probably be afraid - what (to quote CS Lewis) to Professor Otto would have been an example of the "numinous" breaking through.
When the sun danced at Fatima in 1917, the atheists there didn't sit down and blandly ask "I wonder what the natural explanation is for all this?"
No. The record states they were terrified.
First, the record of a couple of eye witnesses (and note they could look at the sun without eye damage for ten minutes, another miracle. Ten seconds is normally enough to cause permanent eye damage) - and note the "numinous" - "It was a terrible moment."
We looked easily at the sun, which for some reason did not blind us. It seemed to flicker on and off, first one way, then another. It cast its rays in many directions and painted everything in different colors--- the trees, the people, the air and the ground. But what was most extraordinary, I thought, was that the sun did not hurt our eyes. Everything was still and quiet, and everyone was looking up. Then at a certain moment, the sun appeared to stop spinning. It then began to move and to dance in the sky until it seemed to detach itself from its place and fall upon us. It was a terrible moment.
Ti Marto (father of Jacinta and Francisco)
It was a remarkable fact that one could fix one's eyes on this brazier of heat and light without any pain in the eyes or blinding of the retina. The phenomenon, except for two interruptions when the sun seemed to send out rays of refulgent heat which obliged us to look away, must have lasted about ten minutes.
Dr. Almeida Garrett, PhD (Coimbra University)
Now the terrified reaction of at least one atheist -
Near us was an unbeliever who had spent the morning mocking at the simpletons who had gone off to Fátima just to see an ordinary girl. He now seemed to be paralyzed, his eyes fixed on the sun. Afterwards he trembled from head to foot and lifting up his arms fell on his knees in the mud, crying out to our Lady.
Fr. Ignacio Lorenco (Alburitel, 11 miles away)
These dry hypotheticals don't take into account the invasion of the "numinous" in these situations. When the disciples saw Christ walking on the water, in the middle of a storm, there's no record they had a dry, intellectual discussion about it. The record states they were terrified.
Rest assured, if an atheist really does see someone truly walking on water, he or she will be drawn far more into the mystery than mere intellectual conjecture.