Spring is the time that boaters need to be especially aware of the weather conditions. You can get weather information from TV, radio or from one of the weather channels on your VHF radio. At certain times of the year, weather can change rapidly and you should continually keep a “weather eye” out in order to foresee changes which might be impending.
Certain signs you can look for indicate an approaching weather change:
- Although weather changes generally come from the west, you should be observant of weather from all directions, so scan the sky with your weather eye, especially to the west.
- A sudden drop in temperature and change in the wind often mean that a storm is near.
- If you have a barometer on your boat, check it every two to three hours. A rapid drop in pressure means a storm is approaching.
- Watch for cloud build up, especially rapid, vertically rising clouds. Be alert for the sound of thunder.
- Watch for lightning and rough water. Remember that boats, particularly sailboats, are vulnerable to lightning if not grounded.
Thunderstorms form when warm, moist air rises, cools and condenses. The thunderstorm develops in three stages:
- The cumulus stage occurs as the warm moist air rises in a great vertical development. You will notice that the top of the cloud formation appears to “boil” as it rapidly rises.
- The mature stage occurs when the cloud formation has reached its maximum height, sometimes 60,000 feet. At this point you will see the top in the shape of an anvil. This is being driven by winds aloft and the front of the anvil will point in the direction that the storm is moving. If you cannot see the anvil shape the storm is either coming toward you or going directly away.
- The dissipation stage occurs as the cloud has released its precipitation and starts to go down. You will first observe a fuzzy, fibrous (called glaciated) top. As the storm continues to dissipate you will see cirrus clouds streaking from the top.
One of the weather phenomena that you may find associated with a thunderstorm is wind sheer. Wind sheer is low mixed turbulence that occurs in front of a thunderstorm.
Thunderstorms contain thunder and lightning that can be used to determine the distance that the storm is from your current location and whether or not the storm is moving toward you or away from you. In order to make this estimate, count the seconds between the time you see the lightning and the time you hear the thunder. Divide this number by 6 and this will be the approximate distance in nautical miles that the storm is from your location. If the time between the flash of lighting and the clap of thunder were 12 seconds, the storm would be approximately 2 nautical miles away. This formula works because of the difference in the speed of light (when you see the lightning) and the speed of sound (when you hear the thunder). By using this calculation several times in a row you should be able to determine if the storm is coming toward you or going away. If it were coming toward you, obviously the seconds between the lightning and thunder would be decreasing. On the other hand, if the seconds between lightning and thunder were increasing, the storm would be moving away.
IF A STORM IS NEAR…
- First and foremost, make sure all aboard are wearing USCG approved PFDs.
- Reduce speed and proceed with caution.
- Close all hatches and ports.
- Head for the nearest shore that is safe to approach and duck into the lee of land.
- Put the bow into the wind and waves at about a 40 degree angle and watch for floating debris.
- Pump out bilges and keep dry.
- Change to a full fuel tank.
- Secure loose items that could be tossed about.
- Keep everyone low in the boat and near the centerline.
- Minimize the danger of having your boat struck by lightning by seeking shelter in advance of a storm. If caught on open water during a thunderstorm, stay low in the middle of the boat.
- If there is lightning, disconnect all electrical equipment. Stay as clear of metal objects as possible.
Be aware that thunderstorms can also include tornadoes and or waterspouts which are much more violent. A waterspout is a small, whirling storm over ocean or inland waters. Its chief characteristic is a funnel-shaped cloud. When fully developed, it extends from the surface of the water to the base of a cumulus cloud. The water in a waterspout is mostly confined to its lower portion.