Summer of 1998 - Beaver Island, MI (northern Lake Michigan).
I was taking a class at the university biological station located on the island for 3 weeks and elected to camp the entire duration. One evening while socializing around the campfire, you could hear thunder and see lightning approaching. I finished my beer, said good night and settled in before the rain started. That started the longest night of my life. The storm hit the island like a freight train! Rain was beating through the seams of the rainfly and tent. Had to mock up paracord through tie-points inside the tent to drape my towel across to keep from being dripped on. Listened for hours as the lightning crashed overhead, the wind was unholy and trees/tree tops fell around me. I thought about making a dash to a structure but figured it would be my luck that I would be crushed 2 feet outside of my tent whereas laying still would have been safe. I made it through the night but I was tired and soggy the next morning. It took a couple days to learn the extent of what had happened since our connections to the mainland were cut. 120 MPH winds, fatalities and injuries on the mainland, roofs gone, homes destroyed and most of the telephone/electric grid was gone on the western half of MI. I was in a 2-man tent: http://blog.mlive.com/chronicle/2008...through_t.html

Spring 2001 - Garden Is., MI
A close 2nd was camping on an island north of Beaver Island a number of years later in early May. Three of us were now working at the biological station and got permission to take 1 of the research boats (an 18' Lund side console) to this other island to camp for the weekend. We were all staying in separate tents. The forecast was good and the run up was beautiful; sunny, warm and Lake Michigan was like glass. Set up camp and started exploring. The next day the wind came up. That night, the wind stayed up, the temps. dropped and it started raining. My gear was solid but one guy's tent filled with water; soaked everything. He was becoming hypothermic by the time he came to my tent in the middle of the night. I had to give him my dry clothes and be creative with anything that wasn't soaked to get him warm. He was starting to lose motor control and get confused. If I could not have got him warm, I would have been looking at sending out a MAYDAY to the Coast Guard with the hope someone would hear it. The next day we were faced with heading back to the mainland in 5-7' cresting waves or waiting it out. Got a weather report on the marine radio stating more wind, more rain, colder temps and bigger waves. We made a run for it and it was scary as hell! I was the driver so I had to feather the throttle so that waves would not swamp us from behind and not drive over the top of the wave in front of us. I still don't know how I didn't sink that boat and kill us all. Fortunately, northern Lake Michigan in early May is about 38-40 degrees F. We wouldn't have suffered long....

Neither stories are bike related but it could happen on a bike tour.