My crewmate and I were killing time waiting for the race to start, when I saw other sailors staring and pointing. Curious, I turned to see the biggest, blackest, meanest-looking thunderstorm cloud I had ever confronted, and it was bearing down on us. I changed course toward the nearby shore and told my one-man crew, Pete, to get the anchor ready to set if the wind fell. Instead, it shot up to about 60 knots.
Pete dropped the anchor while I clawed down the mainsail and pushed it, complete with boom, under the deck. The anchor must not have found bottom yet because we remained broadside to the wind. I was hiked out as far as I could go on our little 17-foot boat, with Pete lying on the weather deck, but the lee rail was buried in water from the pressure of the wind on just the bare mast. Minutes later–it seemed much longer–the weather let up, the anchor caught and we turned into the wind, giving us a chance to clear up the mess and observe the scene: most of the fleet had capsized (the papers estimated about 100 boats).
There were a number of stories to be told about the Governor's Cup, held on Virginia's York River all those years ago, but they all had the same lesson: thunderstorms should be taken seriously. Knowing how thunderstorms work, and how to react to them on the water, is a vital part of safe cruising.
HOW THUNDERSTORMS WORK
Thunderstorms need two things to form: heat and humidity. That is why they most often occur during spring and summer in humid parts of the country. Though they can occur anywhere in the United States, they are much less common in Alaska, Hawaii and on the West Coast.
Cumulus clouds (which take their name from the word, accumulation) form when warm, moist air rises and moisture condenses to form the cloud. Occasionally, a cumulus cloud will continue to build vertically, becoming a cumulonimbus cloud. At about 25,000 feet it encounters cooler temperatures and water droplets coalesce into larger drops that begin to fall. The friction of the falling drops, and their cooling effect, creates downdrafts.
They are rare, but thunderstorms are capable of producing waterspouts, as pictured here, or tornados. At its mature stage, the cloud is a roiling mass of updrafts and downdrafts with temperature changes within it and precipitation in the form of rain, snow or hail being tossed up and down. The friction of all this activity creates great quantities of static electricity, which provides lightning and thunder. The downdrafts become dominant and flow out of the bottom of the cloud, spreading out in all directions as they encounter the surface. Heavy rain, and sometimes hail, pours from the bottom of the cloud. In extreme cases thunderstorms can produce tornadoes or waterspouts.
As the cloud continues to build vertically, the top–now at about 40,000 feet–spreads ice crystals downwind in the characteristic anvil top. At this point, it is already dying. The downdrafts stop further intake of moist air and soon blow themselves out. The dangerous, mature phase of the storm usually lasts about an hour. However, blasts of cold wind from the dying storm can start new updrafts, producing a succession of thunderstorms.
