Public Information Statement
Issued by NWS Portland, ME

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NOUS41 KGYX 301057
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PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE GRAY ME
700 AM EST WED MAR 30 2016

THE NATIONAL WEATHER SERVICE AND THE NATIONAL OCEANIC AND
ATMOSPHERIC ADMINISTRATION HAVE DECLARED THE WEEK OF MARCH 28TH
THROUGH APRIL 1ST TSUNAMI PREPAREDNESS WEEK IN MAINE AND NEW
HAMPSHIRE, AS WELL AS IN THE REMAINDER OF THE COASTAL UNITED
STATES.

...THE GULF OF MAINE TSUNAMI THREAT...

TSUNAMIS AND TSUNAMI-LIKE WAVES CAN ENTER THE GULF OF MAINE
EITHER FROM THE OPEN WATERS OF THE ATLANTIC OR ORIGINATE IN THE
GULF OF MAINE.  THOSE ORIGINATING OUTSIDE THE GULF OF MAINE
WOULD PRODUCE SMALL BUT POTENTIALLY DANGEROUS AND DAMAGING
IMPACTS ALONG THE ENTIRE NORTHERN NEW ENGLAND COAST.  THOSE
ORIGINATING IN THE GULF OF MAINE WOULD ALSO PRODUCE SMALL BUT
POTENTIALLY DANGEROUS AND DAMAGING IMPACTS, BUT USUALLY ONLY TO
A LOCALIZED AREA ALONG THE COAST.

TSUNAMI WAVES ENTERING THE GULF OF MAINE...

THE NORTHERN NEW ENGLAND COAST AND THE GULF OF MAINE ARE
SOMEWHAT PROTECTED FROM A MAJOR TSUNAMI THREAT BY THE SHALLOW
WATERS OF GEORGES BANK AND THE CONTINENTAL SHELF.    WHEN
TSUNAMIS GENERATED OUTSIDE THE GULF OF MAINE ENCOUNTER THE
SHALLOW WATERS OF GEORGES BANK, A PORTION OF THE WAVE ENERGY IS
REFLECTED BACK OUT TO SEA.  MOST OF THE WAVE ENERGY ENTERING THE
GULF OF MAINE WOULD COME THROUGH THE NORTHEAST CHANNEL AND THE
GREAT SOUTH CHANNEL.  BECAUSE OF THE DEEPER WATERS IN THESE
CHANNELS, THE LEADING EDGE OF THE TSUNAMI WAVES WOULD MOVE
FASTER IN THE CHANNELS THAN IN THE SHALLOWER WATERS ON EITHER
SIDE.  THIS WOULD CAUSE MUCH OF THE TSUNAMI WAVE ENERGY TO BE
REFRACTED TO THE RIGHT AND LEFT OF THE CHANNELS.  AS A RESULT,
MUCH OF THE TSUNAMI WAVE ENERGY ENTERING THE GULF OF MAINE
INITIALLY WOULD BE DIRECTED TOWARD THE GEORGES BANK AND NOVA
SCOTIA.  HOWEVER, ADDITIONAL REFLECTIONS AND REFRACTIONS OF THIS
WAVE ENERGY WOULD LEAD TO VERY RAPID AND CHAOTIC FLUCTUATIONS OF
WATER LEVELS IN THE GULF OF MAINE THAT COULD LAST FOR MORE THAN
6 HOURS.  THESE FLUCTUATIONS COULD CAUSE STRONG, DANGEROUS, AND
DAMAGING CURRENTS ALONG THE COAST, AND COULD CAUSE SOME MINOR
INUNDATION AT THE TIME OF HIGH TIDE.

THE TWO MOST SIGNIFICANT TSUNAMI SOURCES OUTSIDE THE GULF OF
MAINE WOULD BE A MAJOR EARTHQUAKE ALONG THE SUBDUCTION ZONE OF
THE PUERTO RICAN TRENCH (JUST TO THE NORTH OF PUERTO RICO) OR A
LARGE SEDIMENT SLIDE ON THE CONTINENTAL SLOPE OF THE EAST COAST.
IN THE CASE OF AN EARTHQUAKE ALONG THE PUERTO RICAN TRENCH, MUCH
OF THE TSUNAMI WAVE ENERGY WOULD BE DIRECTED NORTH TOWARD THE
GULF OF MAINE.  TRAVEL TIME FROM THE INITIAL QUAKE UNTIL THE
TSUNAMI WAVE REACHED THE COAST WOULD BE ABOUT 5 TO 6 HOURS,
ALLOWING PLENTY OF TIME FOR A WARNING OR ADVISORY.  ALTHOUGH
DANGEROUS AND DAMAGING, THE IMPACTS TO NORTHERN NEW ENGLAND OF A
TSUNAMI GENERATED ALONG THE PUERTO RICAN TRENCH WOULD BE
RELATIVELY SMALL COMPARED TO THE POTENTIALLY DEVASTATING IMPACTS
ON PUERTO RICO AND BERMUDA.  THE OTHER SOURCE OUTSIDE THE GULF
OF MAINE WOULD BE A LARGE SEDIMENT SLIDE OR SLUMP ON THE
CONTINENTAL SLOPE.  THE EXACT IMPACTS OF SLIDE OR SLUMP WOULD
DEPEND ON THE ORIENTATION OF THE SLIDE OR SLUMP WITH RESPECT TO
THE NORTHEAST AND GREAT SOUTH CHANNELS AND MAGNITUDE OF THE
SLIDE OR SLUMP.


TSUNAMI WAVES GENERATED IN THE GULF OF MAINE...

SIMILAR TO TSUNAMIS INITIATED OUTSIDE THE GULF OF MAINE,
SEDIMENT SLIDES OR SLUMPS IN THE GULF OF MAINE COULD CAUSE
LOCALIZED TSUNAMI WAVES.  IN THE GULF OF MAINE, SLIDES OR SLUMPS
MOST LIKELY WOULD BE NEAR THE COAST OR ALONG THE NORTHERN EDGE
OF ONE OF THE BANKS OR LEDGES.  IN EITHER CASE, THE EXACT
IMPACTS OF THE TSUNAMI WAVES WOULD DEPEND ON THE ORIENTATION AND
MAGNITUDE OR THE SLIDE OR SLUMP AND WOULD AFFECT ONLY A
LOCALIZED AREA.  THESE SLIDES AND SLUMPS AND THE SUBSEQUENT
TSUNAMI WAVES COULD OCCUR WITHOUT WARNING.

ALTHOUGH TECHNICALLY NOT A TSUNAMI, TSUNAMI-LIKE WAVES CAN
DEVELOP IN CERTAIN SPECIFIC WEATHER SITUATIONS.  THESE ?METEO-
TSUNAMIS?   DEVELOP WHEN AN ATMOSPHERIC PRESSURE WAVE MOVES
ACROSS THE GULF OF MAINE AT JUST THE RIGHT SPEED, CREATING A
HARMONIC RESONANCE WITH A DEVELOPING TSUNAMI-LIKE OCEAN WAVE
BELOW.  THIS RESONANCE WOULD ALLOW THE OCEAN WAVE TO GROW WITH
TIME AS BOTH WAVES MOVE IN UNISON.  SINCE THE FORWARD SPEED OF
THE TSUNAMI-LIKE WAVE IS DETERMINED BY THE DEPTH OF THE OCEAN,
THE ATMOSPHERIC FEATURE NEEDS TO MOVE AT THE JUST THE RIGHT
SPEED AS DETERMINED BY THE OCEAN DEPTH.  IN THE GULF OF MAINE,
VERY FAST MOVING WEATHER SYSTEMS COULD MEET THIS REQUIREMENT.
IN ADDITION, THE MOVEMENT OF BOTH THE ATMOSPHERIC AND THE
TSUNAMI-LIKE WAVES WOULD NEED TO BE TOWARD THE COAST.  WHILE
RARE, METEO-TSUNAMIS DO OCCUR IN THE GULF OF MAINE.  IN FACT, A
METEO-TSUNAMI IS BELIEVED TO HAVE CAUSED THE UNUSUAL TIDAL
FLUCTUATIONS THAT WERE OBSERVED ALONG THE MID-COAST OF MAINE IN
OCTOBER 2008.

$$

JENSENIUS
NATIONAL WEATHER SERVICE
GRAY, MAINE

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