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Public Information Statement
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000
NOUS42 KCAE 181032
PNSCAE
SCZ015-016-018-020>022-025>031-035>038-041-GAZ040-063>065-077-191200-

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE COLUMBIA SC
635 AM EDT WED MAR 18 2015

NATIONAL FLOOD AWARENESS WEEK...DAY THREE.

TROPICAL CYCLONE AND INLAND FLOODING.

WHEN IT COMES TO TROPICAL CYCLONES...WIND SPEEDS DO NOT TELL THE 
WHOLE STORY. INTENSE RAINFALL...NOT DIRECTLY RELATED TO THE WIND 
SPEED OF A TROPICAL CYCLONE...OFTEN CAUSES MORE DAMAGE.  SINCE THE 
1970S...INLAND FLOODING HAS BEEN RESPONSIBLE FOR MORE THAN HALF OF 
THE DEATHS ASSOCIATED WITH TROPICAL CYCLONES IN THE UNITED STATES. 
TYPICALLY...GREATER RAINFALL AMOUNTS AND FLOODING ARE ASSOCIATED 
WITH TROPICAL CYCLONES THAT HAVE A SLOW FORWARD SPEED OR STALL OVER 
AN AREA.

WHAT DO I NEED TO KNOW ABOUT INLAND FLOODING FROM TROPICAL
CYCLONES?

INLAND FRESHWATER FLOODS ACCOUNTED FOR MORE THAN HALF (59%) OF U.S. 
TROPICAL CYCLONE DEATHS OVER THE PAST 30 YEARS. RAINFALL IS 
TYPICALLY HEAVIER WITH SLOWER MOVING STORMS AS SLOWER MOVING
TROPICAL CYCLONES ALLOW HEAVY RAIN TO PERSIST OVER A LOCATION.

WHAT TYPES OF INLAND FLOODING ARE CAUSED BY TROPICAL CYCLONES?

FLASH FLOODING OCCURS IN CREEKS...STREAMS AND URBAN AREAS WITHIN
A FEW MINUTES OR HOURS OF EXCESSIVE RAINFALL.  RAPIDLY RISING 
WATER CAN REACH HEIGHTS OF 30 FEET OR MORE. STREETS CAN BECOME
SWIFT MOVING RIVERS AND UNDERPASSES CAN BECOME DEATH TRAPS.

RIVER FLOODING OCCURS FROM HEAVY RAINS ASSOCIATED WITH DECAYING
HURRICANES OR TROPICAL STORMS...AND IN EXTREME CASES...RIVER 
FLOODS CAN LAST A WEEK OR MORE.

HOW DO I KNOW HOW SERVE A FLOOD WILL BE?

WITHIN FLOOD WARNING PRODUCTS...THE NATIONAL WEATHER SERVICE COVEYS
THE MAGNITUDE OF OBSERVED OR FORECAST FLOODING USING FLOOD SEVERITY
CATEGORIES. THESE FLOOD SEVERITY CATEGORIES INCLUDE MINOR FLOODING...
MODERATE FLOODING AND MAJOR FLOODING. EACH CATEGORY HAS A DEFINITION
BASED ON PROPERTY DAMAGE AND PUBLIC THREAT.

MINOR FLOODING: MINIMAL OR NO PROPERTY DAMAGE...BUT POSSIBLY SOME
PUBLIC THREAT OR INCONVENIENCE.

MODERATE FLOODING: SOME INUNDATION OF STRUCTURES AND ROADS NEAR 
STREAMS. SOME EVACUATIONS OF PEOPLE AND OR TRANSFER OF PROPERTY 
TO HIGHER ELEVATIONS ARE NECESSARY.

MAJOR FLOODING: EXTENSIVE INUNDATION OF STRUCTURES AND ROADS WITH 
SIGNIFICANT EVACUATIONS OF PEOPLE AND OR TRANSFER OF PROPERTY TO
HIGHER ELEVATIONS.

THE IMPACTS OF A FLOOD VARY LOCALLY.  FOR EACH NWS RIVER FORECAST
LOCATION...FLOOD STAGE AND THE STAGE ASSOCIATED WITH EACH OF THE NWS
FLOOD SEVERITY CATEGORIES ARE ESTABLISHED IN COOPERATION WITH LOCAL 
PUBLIC OFFICIALS.  INCREASING RIVER LEVELS ABOVE FLOOD STAGE  
CONSTITUTE MINOR...MODERATE...AND MAJOR FLOODING.  IMPACTS VARY FROM
ONE RIVER LOCATION TO ANOTHER BECAUSE A CERTAIN RIVER STAGE HEIGHT 
IN ONE LOCATION MAY HAVE AN ENTIRELY DIFFERENT IMPACT THAN THE SAME 
LEVEL ABOVE FLOOD STAGE AT ANOTHER LOCATION.

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