CONCEPT FOR THE DAY - COASTAL FLOODING and MARINE WEATHER
Tuesday, 25 April 2017
A coastal flood occurs when low lying land
areas bordering a large body of water are inundated. Coastal flooding
may be caused by abnormal rise in water level associated with an
approaching ocean storm or by large breaking waves on the shore from
large ocean swells. The extent of coastal flooding depends upon the
tide levels, the underwater and shoreline topography and the runoff
from rivers and estuaries.
Coastal floods are often associated with high water from a storm
surge, caused by winds generated by tropical (hurricanes) or
extratropical cyclones. Coastal flooding can be produced also by a tsunami,
a seismic sea wave produced by earthquakes, landslides or volcanic
activity; these waves have been erroneously called tidal waves. Alaska,
Hawaii and the Pacific coast are most vulnerable to a tsunami.
The greatest danger and damage associated with most tropical
cyclones (hurricanes) is the storm surge. A storm surge is a dome of
water, perhaps 50 miles wide that sweeps across the coastline ahead of
a tropical cyclone landfall. The magnitude of a storm surge depends
upon the strength of the storm, the ocean bottom conditions where the
surge comes onshore, the storm's movement relative to the shoreline,
and the astronomical tides at landfall time.
In addition, the destruction of the storm surge is often
compounded by the hammering effect of the breaking waves. Because many
tropical cyclones produce excessive rainfall rates and total amounts of
precipitation even after landfall, they may also be responsible for
floods and flash floods. The strong and gusty winds, coupled with the
possibility of tornadoes, are added perils to residents of areas near
the landfall of a hurricane.
Coastal floods and beach erosion can also be associated with
extratropical cyclones, such as the "nor'easters", that may batter the
East Coast from Cape Hatteras to Maine, especially during the winter
season. Coastal flood watches and warnings are issued by certain
designated National Weather Service Offices and pertain to the region
extending from the ocean beaches inland, including waterways, estuaries
and river mouths.
The National Weather Service issues various public statements
for tropical weather systems as well as for other types of situations
that can cause coastal floods. These statements follow the advisory,
watch and warning format previously described, and they are intended to
inform the coastal residents and commercial and recreational marine
interests of a potentially hazardous weather situation. A full
description of these statements appears in the Supplemental Information…In Greater Detail that follows.
To be submitted on the lines for Tuesday on the Investigations
Manual, Week 12 Chapter Progress Response Form.
- The most damaging aspect of a hurricane to coastal
inhabitants is usually the [(high wind), (storm
surge), (heavy rain), (low pressure)].
- Coastal flooding is not caused by [(tropical
systems) (extratropical systems) (normal lunar tides) (tsunamis)].
SUPPLEMENTAL INFORMATION...IN GREATER
Tuesday, 25 April 2017
SPECIFIC TROPICAL & MARINE
The National Weather Service issues various marine-related
advisories, watches and warnings to the public that pertain to a
variety of severe weather conditions as well as unusual water, waves
and current conditions that could affect life and property. The area of
responsibility includes the coastal waters and the open waters of the
Atlantic and Pacific Oceans and the Gulf of Mexico. Some of these
statements cover tropical weather systems, including tropical storms
and hurricanes. The Ocean Prediction Center (formerly called Marine
Prediction Center or MPC), another component of the National Centers
for Environmental Prediction (NCEP), issues marine warnings for
situations not involving tropical weather systems. Their responsibility
covers coastal and offshore waters as well as the high seas for
latitudes poleward of 30 degrees north, while the Tropical Prediction
Center is responsible for waters equatorward of this latitude. The
Pacific Tsunami Warning Center (PTWC) in Honolulu, HI and the West
Coast/Alaska Tsunami Warning Center (WC/ATWC) in Palmer, AK issue
tsunami watches and warnings for Pacific basin. The National Hurricane
Center (NHC) in Miami, FL, a part of the Tropical Prediction Center, is
responsible for issuing statements concerning tropical weather systems
for the North Atlantic Basin (including the Gulf of Mexico and the
Caribbean Sea) and the eastern Pacific Basin (to 140 degrees West
longitude). The Pacific Hurricane Center in Honolulu, HI monitors the
Central Pacific to the International Date Line (at 180 degrees). The
Hawaiian Islands are located within this region.
The following list includes terminology used by the National
Weather Service for those public statements pertaining to tropical
- Tropical storm watch --
Issued by the National Hurricane Center to alert the public
in a coastal area when a threat of tropical storm conditions (sustained
winds within the range 34 to 63 knots or 39 to 73 mph) is predicted
within 36 hours.
- Tropical storm warning --
Issued to warn the public of imminent tropical storm
conditions (sustained winds within the range 34-63 knots), which are
expected in a specified coastal area within 24 hours or less.
Issued by the National Hurricane Center for specific areas
that an incipient hurricane condition (to include winds greater than 63
knots) poses a possible threat to coastal areas generally within 36
hours. The public should be prepared to take precautionary action if a
hurricane warning were issued.
- Hurricane warning --
Issued to warn the public that one-minute sustained surface
winds of 64 knots (74 mph) or higher associated with a hurricane are
expected in a specified coastal area within 24 hours or less. A
hurricane warning can remain in effect when dangerously high water and
exceptionally high waves continue although winds may be less than
hurricane force. The public should take immediate action. For mariners,
the hurricane warning signals for this condition are (a) two flags that
are square, red with black center by day and (b) a vertical arrangement
of two red lanterns surrounding a white lantern by night.
The following statements can be issued for several types of
events, not limited to tropical weather systems:
- Coastal flood watch --
Issued to alert coastal residents of the possibility of the
inundation of land areas along the coast within the next 12 to 36
- Coastal flood warning --
Issued to warn residents of coastal areas that land areas
along the coast will be inundated by sea water above the typical tide
- Heavy surf advisory --
Issued to inform the public that high ocean surf may pose a
threat to life or property. The criteria for such advisories depend
upon the locale, but typically, these include minimum wave heights of
between 8 to 12 feet with periods on the order of 10 seconds. The heavy
surf is typically produced by large ocean swells associated with a
distant storm system over the ocean, supplemented at times by
astronomical high tides.
- Tsunami watch/warning --
Issued by the National Weather Service to either alert or
warn residents in regions along the Pacific Ocean that an impending
tsunami (seismic sea wave) may cause damage to low lying regions. The
type of bulletin is based on the magnitude and the location of the
source underwater geological event. The content and format are similar
to coastal flood watches and warnings. Usually, the tsunami warning is
issued for a limited area around the earthquake epicenter, with the
time of tsunami's arrival within 2 to 3 hours.
The following marine weather statements can be issued:
- Small-craft advisory --
Issued to advise mariners of sustained (exceeding two
hours) weather and/or sea conditions, either present or forecast,
potentially hazardous to small boats. These conditions generally
include winds of 18-33 knots (21-38 mph) and/or dangerous wave
conditions. Small craft advisories may be issued also for hazardous sea
conditions or lower wind speeds that may affect small craft operations.
Advisories can be issued up to 12 hours prior to the onset of adverse
conditions. The small-craft advisory signals for this condition are (a)
one triangular red pennant by day, and (b) a red lantern over a white
lantern by night.
- Small-craft warning --
Issued as a warning for marine interests of impending winds
up to 28 knots (32 mph); used mostly in coastal or inland waters.
A storm warning for marine interests of impending winds
associated with extratropical low pressure systems with speeds ranging
from 34 to 47 knots (39 to 54 mph) within a 24-hour period of
anticipated conditions. The storm warning signals for this condition
are (a) two triangular red pennants by day, and (b) a white lantern
over a red lantern by night.
- Storm (also known as
whole-gale) warning --
A warning for marine interests of impending winds
associated with an extratropical low that are greater than 48 knots (55
mph). The storm-warning signals for this condition are (a) one square
red flag with black center by day and (b) two red lanterns by night.
marine warning --
A warning issued for marine interests of potentially
hazardous over-water events of relatively short duration, usually up to
2 hours. Typically, these warnings are issued for strong to severe
thunderstorms that may include strong winds, frequent lightning, heavy
rains or waterspouts.
The National Hurricane Center (Tropical Prediction Center)
issues Tropical Weather Outlooks. The information
contained in these guidance products is used on television
weathercasts. These Outlooks include levels of risk.
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Prepared by Edward J. Hopkins, Ph.D., email firstname.lastname@example.org
© Copyright, 2017, The American Meteorological Society.