Wind - Downbursts



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Caused by thunder-storms, localized strong winds as high as 130 miles per hour can hit with little or no warning.






DOWNBURSTS
The Sudden Winds
Information provided by:

U.S.C.G.
Boating Education Branch
800-368-5647
 

DOWNBURSTS
Perhaps you’ve heard news reports about the effects of “wind shear” on aircraft during takeoffs or landings. A similar phenomenon may also occur on the water and effect boats. Caused by thunder­storms, these localized, strong winds are called DOWNBURSTS. Although there are several ways in which these form, they all exhibit certain charac­teristics: 1) winds may exceed 130 mph - much faster than even the normally gusty thunderstorm winds, 2) the strong winds hit suddenly with little or no warning, and 3) the strongest winds affect a rela­tively small area.

DOWNBURSTS come from thunderstorms. Therefore, whenever a boater encounters a thunder­storm, a DOWNBURST is possible. This is true if the thunderstorm is all by itself or is part of a series, such as a squall line.

When a DOWNBURST first strikes the surface, it is often concentrated in an area less than 3 miles across. This is generally where the most extreme winds can be found. The term MICROBURST is often used in describing this phase. After striking the ground, the winds begin to spread out, eventu­ally covering an area up to 30 or 40 miles across. However, MICROSBURSTS can still be embedded in the general DOWNBURST.




DOWNBURSTS are usually short-lived high winds lasting only a few minutes. However, one thunder­storm can produce a series of these winds affecting a swath several miles long and lasting an hour or more.

DOWNBURSTS hit so rapidly that few signs may be available to alert the boater as to its presence.  Blowing spray under or slightly ahead of a thunder­storm may be the only indicator. However, the best rule is, avoid ALL thunderstorms if possible. If not, expect and prepare for the worst whenever a thunderstorm is encountered.




The hazards of Downbursts are:
    • Extreme, sudden winds which can tip a sailboat beyond its range of upright stability.
    • Heavy seas that can capsize powerboats too.
    • High winds that can blow equipment off the deck and cause persons on board to lose balance and fall overboard.
Boats caught out on open water under these conditions can encounter a downburst without expecting it. DOWNBURSTS are generally short-lived; lasting less than ten minutes. This fact makes predicting their occurrence almost an impossible task. The sudden loss of the sailing vessel “Pride of Baltimore” in the Atlantic near Puerto Rico in 1986 was attributed to a downburst wind. Witnesses claim in less than two minutes, the ship was blown over, filled with water, and sank. Although this tragedy involved a larger sailing vessel on the open ocean, similar dangers have been experienced by vessels on inland or inshore waters.

Thunderstorms can create several downbursts in succession, with varying degrees of intensity. A thunderstorm might even generate a combination of downbursts and tornadoes.

 

Weather Information

The best source of current weather information is the continuous National Weather Service broad­casts. Seven frequencies between 162.400 and 162.550 MHz have been set aside for this purpose. However, three (162.400, 162.475, and 162.550) are the most common. Taped information is recycled approximately every five minutes with broadcasts updated no less than every 3 to 6 hours. In the event of unusual or severe weather, the program­ming may be interrupted and broadcasts are done live.

The Coast Guard also broadcasts special marine weather information, including small craft adviso­ries, on VHF Channel 22. Visual warnings are no longer operated by the National Weather Service. However, certain organizations have continued to display lights and flags when rough weather is expected.

Protection

    • Turn your craft with the bow facing into the wind, and “reef” your sails if you have them. These actions help minimize wind resistance.
    • Secure all loose objects and rigging on-deck, and make certain hatches or other openings are covered.
    • Wear your personal flotation device, making sure it fits securely. Keep other lifesaving equipment readily accessible, including inflatable rafts and visual distress signals.
 

Storm Warnings

Smail Craft Advisory:
Generally associated with sustained winds 18 to 33 knots, or waves hazardous to small boats. These are not issued during the winter months along the Great Lakes.

Gale Warning:
Sustained winds 34 to 47 knots.

Storm Warning:
Sustained winds 48 knots or more.

Hurricane Warning:
Sustained winds 64 knots or more associated with a hurricane.

Special Marine Warning:
Winds of 35 knots or more lasting generally less than 2 hours. These are usually associated with an individual thunderstorm or an organized series of thunderstorms (squall line, cold front).


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EVEN THE BEST BOATERS CAN FIND THEMSELVES IN SERIOUS TROUBLE ON THE MILDEST OF DAYS ON THE WATER. PARTICIPATION IN THIS SPORT IS A STRENUOUS ACTIVITY. CONSULT YOUR PHYSICIAN BEFORE UNDERTAKING ANY SUCH ACTIVITY. PLEASE BE AWARE THAT EACH BOATER TAKES FULL RESPONSIBILITY FOR HIS OR HER OWN SAFETY, AND IS TOTALLY RESPONSIBLE FOR ASSESSING THE DANGER LEVEL AND ACCEPTING THE CONSEQUENCES OF PARTICIPATING IN THIS SPORT.


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