Weather Watch

Posted: July 1, 2013

Know these indicators of deteriorating weather, and stay safe.

By: Wayne Stacey, U.S. Coast Guard Division of Boating Safety

Despite the best technology and advances in forecasting, weather remains extremely local and changeable. The keys to avoiding dangerous weather include checking forecasts frequently and learning to recognize signs of deteriorating conditions.

Checking the weather before you go out on the water — including immediately before departure — is one important aspect of boating safely. Unfortunately, local weather reports are often general and too infrequent. The National Oceanic and Atmospheric Administration (NOAA) has a radio network that covers all United States coastal areas. You can tune to the NOAA weather radio station in your area and get the latest report around the clock using a special NOAA weather radio or any marine VHF radio. For more information, visit nws.noaa.gov/om/marine/home.htm.

But don’t rely on forecasts alone. Large bodies of water and indented coastal areas can have highly variable local weather conditions. For example, wind speed can increase dramatically and even differ from the prevailing direction as wind is funneled through narrow channels. Geological features such as cliffs or high coastal ground can cause local turbulence.

Since weather is always susceptible to quick and unexpected change, staying tuned to local marine weather reports is smart, but doing so doesn’t replace a good “weather eye” and constant situational awareness. Here are some things you can work on before you hit the water:

- Know the direction from which most storms originate in your area, and keep a closer watch in that direction while you’re on the water, but don’t forget to scan in all directions.While planning your trip, note the location of and the approximate time it will take you to get to an accessible safe harbor, if you must change plans due to weather.

- Make sure you know how to use a sea drogue or sea anchor, or things that could be used as makeshift substitutes.

- Know the meanings and locations of shore-based storm signals in your area.

- Be aware of storm warnings. If the wind speed is above a certain threshold (usually 21 to 33 knots), a Small Craft Advisory is issued, meaning all vessels less than 65 feet in length should exercise caution. When wind speeds reach 34 knots and greater, a gale warning is issued. The U.S. Coast Guard recommends that all mariners without the proper experience seek safe mooring before gale warnings are issued.

- Learn how to read clouds and other weather signs. Take a boating weather course, buy a good reference book or take advantage of available online tips.

Stay Alert

Remaining alert and attuned to changes that can signal impending bad weather is always important on the water. Watch for these signs:

- A sudden drop in temperature and change in the wind often means a storm is near. Strong winds that start in the morning are particularly worrisome, because the longer the wind blows, the larger the waves.

- Listen for thunder and watch for lightning and rough water. Boats, particularly sailboats, are vulnerable to lightning if not grounded.

- Fog can create problems in inlets and bays or open water. Fog typically forms during temperature changes in early morning or evening and can last for long periods.

- High pressure generally indicates fair weather, while low pressure means storms are more likely. However, the rate of change in barometric pressure is a more important indicator. If you have a barometer on board, check it every two to three hours. A large change in pressure will signal a large change in weather and an increase in wind strength.

Take note of cloud formations:

- Note cloud buildup, especially rapid, vertically rising clouds. Puffy or cumulus clouds that show a lot of vertical development indicate unstable air. The greater the vertical development of the cloud, the greater the instability. Thunderstorm clouds have the greatest vertical development, and the associated weather can be violent.

- Other cloud patterns to note include clouds lowering and thickening; clouds increasing in number and moving fast across the sky; veils or sheets of gray clouds increasing on the western horizon; and clouds moving in different directions at different heights.

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