Thunderstorms are created when warm, moist air rises, cools and condenses.
It swells into mounds of thick, billowy cumulous clouds that quickly darken into the towering ominous-looking cumulonimbus clouds characteristic of thunderstorms.
Consider the formation of this thick, dark cloud an unmistakable thunderstorm warning, and head immediately for a safe anchorage. The transition from a small cloud into a turbulent, electrified storm front can occur in as little as 30 minutes. The barometer will drop quickly and strong, gusty winds and heavy rains with thunder and lightning will soon follow. Fortunately, few squalls last more than an hour.
The sharper, darker and lower the front edge of the cloud, the more severe the storm. The anvil-shaped top of the storm cloud points in the direction that the storm is traveling.
In summer, afternoon thunderstorms are likely to occur over water when the humidity and temperature ashore are high. Hot air radiates upward from land surfaces heated by the sun. Moisture from a nearby body of water is absorbed by the warm air, which rises to begin the formation of thunderheads.
They usually appear as swift-moving black clouds, often approaching from the northwest southwest, south or west at speeds of 25-35 knots.
You can determine the distance of an approaching thunderstorm by counting the number of seconds between the lightning flash and the thunder clap, and dividing by five.
That will give you the distance in miles you are from the storm. For example, if the time lapse between the lightning flash and the thunder clap is 10 seconds, divide by 5. The storm is approximately 2 miles away from you.
Another handy tip that a thunderstorm is near is to tune your radio to any AM station. Thunderstorms will create static crackling on a station that would otherwise sound clear.
If you are about to be caught in a Thunderstorm....
Once the storm hits...
- Make sure everyone aboard is wearing a life jacket.
- Secure all loose gear, hatches or ports.
- Determine your location and the best course back to shelter.
- Keep a sharp lookout for the other boats and obstructions.
- Try to take the first (and heaviest) gusts of wind on the bow, not abeam. Heading into the wind is the most seaworthy position for most small boats.
- Approach waves at a 45 degree angle to keep the propeller underwater, to reduce pounding, and to provide a safer and more comfortable ride.
- If there is lightning, unplug radios and all electrical equipment.
- Stay low. Don't make yourself the tallest target. Keep away from metal objects that aren't grounded to the boat's protection system.