Hurricane Saftety Awareness Week - Wednesday

The National Weather Service has declared the week of July 15th
through 19th HURRICANE SAFETY AWARENESS WEEK in New England.
This is the third in a series of five public information
statements to be issued by the National Weather Service Office
in Graycontaining information on hurricanes and hurricane safety.

STORM SURGE, WAVES, AND MARINE SAFETY

The storm surge is a large dome of water that is pushed toward
the shore by the force of the winds circulating around the storm.
This advancing surge combines with the normal tides to create
the hurricane storm tide, which can increase the mean water level
15 feet or more. The greatest storm surge generally occurs just
to the right of the storm track, where the strongest winds of
the storm are blowing onshore, perpendicular to the coast. In
addition to the surge, wind driven waves in that area can also
cause considerable damage to structures. This rise in water level
due to the surge can result in severe flooding in coastal areas,
particularly when the storm surge coincides with the normal high
tides. For areas of the coast less than 10 feet above mean sea
level, the danger from storm surge can be tremendous.

Along the New Hampshire and Maine coast, the greatest threat of
damage from storm surge lies in the beach areas south of Portland
and Penobscot Bay.

In addition to the speed and intensity of the hurricane, the level
of surge in a particular area is also determined by the slope of
the underwater topography and the shape of the coast line. A
shallow slope and the funneling effects of a bay will contribute
to a greater surge. Areas with a steeper continental shelf will
not see as much surge, although large breaking waves can still
present major problems. Storm tides, waves, and currents in
confined harbors can severely damage ships, marinas, and
pleasure boats.  
 
In northern New England, the greatest factor in determining the
effects of a storm surge is the timing of the surge with respect
to the astronomical tides. If the storm surge hits at the time of
low tide, little if any coastal flooding will occur. If, however,
the surge hits at high tide, considerable coastal flooding, beach
erosion, and other damage is possible. Unfortunately, the exact
timing of landfall in northern New England is often difficult to
predict very far in advance, so plans should be made based on the
possibility the surge could strike at high tide.

Wave and current action associated with the tide also causes
extensive damage. Water weighs approximately 1700 pounds per
cubic yard, and extended pounding by frequent waves can demolish
any structure not specifically designed to withstand such forces.
Waves generated from distant or approaching storms can also present
a hazard to those who are near the ocean. Strong rip currents can
carry even strong swimmers out to sea, and unexpected large waves
can wash people from rocks.

Hurricanes have been the cause of many maritime disasters and,
unfortunately, there is no single rule of thumb that can be used by
mariners to ensure safe separation from a hurricane at sea. In order
to minimize risk, mariners should allow for a large margin of error
in the hurricane track and intensity forecasts. Today, even as our
understanding of and ability to forecast hurricanes increases,
there is still considerable error in forecasting the movement and
intensity of these systems.

Average errors in the hurricane track forecast increase considerably
as the forecast projection increases. The following list gives
average errors of hurricane forecasts for the 5-year period from 2014
to 2018. Note that errors for storms in northern New England are
likely greater than these "average" values due to the acceleration
that often occurs south of New England and due to the comparatively
fast movement of the storms in New England waters.

       Forecast projection       Average Error
            12 hours                26 n mi
            24 hours                41 n mi
            48 hours                68 n mi
            72 hours               102 n mi
            96 hours               151 n mi
           120 hours               198 n mi

For those with boats, it's important to plan ahead. Know exactly what
you need to do and how long it will take you to accomplish the
necessary tasks. Keep in mind that others will also be taking
preparatory actions too, so you should leave yourself additional time.
 
If you plan to leave your boat in the water, consider the possible
effects of the storm tide and waves. Make sure your anchor is
sufficientto hold the boat, and have enough anchor line to account
for the storm tide. Secure or remove all non-permanent equipment from
the deck. Never try to ride out the storm on your boat; you will
endanger your life and possibly the lives of rescuers.

If you are able to put your boat on a trailer, get it out of the water
early. If you wait too long, you may be in a long line. If possible,
store your boat inside a garage. However, if you leave your boat
outside, put it in a sheltered location, and secure it to sturdy
objects such as large trees.

QUESTION OF THE DAY:  What was the greatest loss of life associated
with any storm surge in the United States?

While not all details are known, the category 4, Galveston, Texas
hurricane of September 8, 1900, caused the greatest loss of life
from a storm surge. Not only was it the greatest loss of life from
a storm surge, it was also the greatest loss of life in the United
States associated with any weather-related disaster. The hurricane
created an 8 to 15 foot surge that inundated all of Galveston Island,
as well as other portions of the nearby Texas coast. This surge was
largely responsible for the estimated 6,000 to 12,000 deaths
attributed to the storm. The damage to property was estimated at
$30 million.

Fortunately, satellites, computers, advanced sensing and prediction
techniques, and better communication systems allow meteorologists to
better predict and warn the public of impending hurricanes.

Other notable surges occurred with Hurricane Andrew (17 feet),
Hurricane Hugo (20 ft), and Hurricane Camille (24.6 feet). The 1938
hurricane that affected New England caused a 10 to 12 ft surge in
Narragansett and Buzzards Bays.

FACT FOR THE DAY: The location with the greatest potential for storm
surge along the northern New England coast is the Penobscot River
near Bangor, Maine. Computer model estimates indicate that the
funneling effect of the Penobscot Bay and River could lead to a
23 foot tide for a Category 3 hurricane moving north at 40 mph.

Here's a list of the other topics covered in statements issued
this week:

Monday - Tropical Cyclones, Tropical Storms, and
         Hurricanes--The Basics
Tuesday - Hurricane Winds and Tornadoes
Thursday - Inland Flooding
Friday - The Forecast Process--Statements, Watches, and Warnings

For additional information about hurricanes and hurricane safety, visit
the National Hurricane Center's web site at:

http://www.nhc.noaa.gov/

$$

Watson
National Weather Service
Gray...Maine

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