

461 

AGNT40 KWNM 040300

MIMATN



MARINE WEATHER DISCUSSION FOR N ATLANTIC OCEAN

NWS OCEAN PREDICTION CENTER WASHINGTON DC

1100 PM EDT SAT SEP 3 2016



.FORECAST DISCUSSION: MAJOR FEATURES/WINDS/SEAS/SIGNIFICANT

.WEATHER FOR THE NORTH ATLANTIC OCEAN W OF 50W FROM 30N TO 50N.



THE SAT IMG INDC TROPICAL STORM HERMINE OVER THE CENTRAL WATERS

WITH A RIDGE JUST N OF THE WATERS. ALL THE OBSERVATIONS INCLUDING

THE ASCAT PASS AT 1450Z HAVE HIGHER WINDS OVER THE CENTRAL WATERS.

BUOY 44014 IN VIRGINIA BEACH IN THE PAST FEW HOURS HAD WINDS 35 TO

40 KT AND GUST TO 45 KT WITH 15 TO 17 FT SEAS. AT 00Z THE NCEP MAP

HAS POST-TROPICAL HERMINE OVER THE CENTRAL WATERS AND WEAK HIGH

PRES CENTERS INLAND W AND NW OF THE STORM WITH A THIRD CENTER 1023

MB JUST NE OF THE BALT CANYON. THE PRES GRADIENT IS VERY TIGHT

OVER THE CENTRAL WATERS BUT FAIRLY RELAXED ELSEWHERE. THE HIGHEST

SEAS ARE OVER THE CENTRAL WATERS WITH PEAKS TO 26 FT. OVER THE FAR

N AND FAR S THE SEAS RANGE BETWEEN 3 AND 6 FT. NWW3 WAVE MODEL HAS

INITIALIZED WELL WITHTHE OBSERVED SEAS PATTERN BUT JUST UNDERDONE

BY 2 FT FOR THE PEAK VALUE. THE ECMWFWAVE HAS ALSO INITIALIZED

WELL BUT ALSO UNDERDONE BY 3 FT WITH THE PEAK VALUE.



THERE IS SOME ENERGY THAT STRETCHES FROM AN UPPERLELVEL TROF OVER

THE MID WEST THRU THE CENTRL WATERS AND CONTINUES E. THE MODEL

SUGGEST MORE ENERGY TO PILE IN THE TROF WHICH WILL EVENTUALLY

CLOSE UP AND PUSH THE ENERGY OVER THE CENTRAL WATERS MON AND THAT

SHOULD KEEP THE STORM OVER THE WATERS. IN THE EXTENDED PERIOD THE

UPPERLEVEL RIDGE TO THE E OF THE WATER WILL BLOCK THE ENRGY FORM

ADVANCING E AND THAT SHOULD KEEP THE ENERGY TRAPPED IN THE CLOSED

LOW LONGER OVER THE WATERS. THE RIDGE TO THE E WIL WEAKEMN AND

ALLOW THE ENERGY TO GLIDE NE.



THE GLOBAL MODELS GFS/ECMWFHR/UKMETHR/CMC HAVE INITIALIZED WELL

WITH THE 00Z OBERVATIONS WITH JUST VERY MINOR DIFFERENCES IN THE

EXTENT OF THE WIND FIELD AROUND THE STORM WITH GFS SHOWING A

LARGER AREA. THE MODELS HAVE DIFFERENCES ON THE TRACK OF THE STORM

AND THE DIFFERENCES ARE EVEN GREATER WHEN THE MOVEMENT OF STROM

SLOWS DOWN BETWEEN 05/1200Z AND 07/0000Z. THE MODELS START TO COME

TO BETTER AGREEMENT AFTER 07/0000Z AS THE SYSTEM SHOW SIGNS OF

MOVING NE. OTHERWISE WILL CONTINUE TO FOLLOW THE NHC TRACK OF THE

STORM AND ADJUST WINDS ACCORDINGLY. WILL RETAIN THE FRCST WINDS

AND MAKE ADJUSTMENTS ACCOERDINGLY.



------------------------------------------------------------------

PREVIOUS DISCUSSION...



BUOY 44014 HAS BEEN REPORTING SUSTAINED 40 TO 50 KT WINDS OVER 

THE PAST SEVERAL HOURS...WITH HIGHEST PEAK GUST OF 64 KT AT 

1722Z. THE CENTER OF HERMINE PASSED VERY CLOSE TO THIS BUOY THIS 

MORNING AS IT REPORTED LOWEST PMSL AND LIGHT WINDS. HERMINE'S 

WIND FIELD HAS TAKEN ON A MORE CLASSIC EXTRATROPICAL APPEARANCE 

AS LATEST HRRR INDICATING THE STRONGEST WINDS HAVE TRANSITIONED 

AWAY FROM THE LOW CENTER AND NOW LIE OVER THE N AND NW QUADRANT 

JUST POLEWARD OF THE OCCLUDED AND BENT BACK FRONT. HERMINE IS 

UNDOUBTEDLY INTENSIFYING AS A POST TROPICAL CYCLONE GIVEN ITS 

PRESENTATION ON THE LATEST SATELLITE IMAGERY AS WELL AS RECENT 

OBS...AND COULD BE CLOSE TO AGAIN ATTAINING HURCN FORCE WINDS. 

ITS WIND FIELD SHOULD BEGIN TO EXPAND SIGNIFICANTLY THROUGH 

SUN/SUN NIGHT. THE 12Z MODELS CONTINUED TO SHOW LITTLE RUN TO 

RUN CONSISTENCY WITH THE 12Z ECMWF/UKMET NOW WELL EAST OF THE 

12Z GFS SUN AND SUN NIGHT. VERSUS THEIR RESPECTIVE PREVIOUS RUNS 

BOTH THE 12Z ECMWF AND 12Z UKMET TRENDED EASTWARD. FOR WIND 

GRIDS WILL BE DOING BEST TO BE CONSISTENT WITH THE NHC ADVISORY 

WHILE STILL REPRESENTING THE EXTRATROPICAL NATURE OF THE WIND 

FIELD.  



MODEL DISCREPANCY FURTHER INCREASES LATE IN THE FORECAST PERIOD 

TUE THROUGH THU NIGHT AS THE 12Z ECMWF WEAKENS THE ASSOCIATED 

UPPER LOW AND KICKS THE OPEN UPPER TROUGH NE NEARLY A FULL TWO 

DAYS PRIOR TO THE 12Z GFS/UKMET. NEEDLESS TO SAY HAVE LITTLE TO 

NO FORECAST CONFIDENCE WITH THE NT1/NT2 FORECASTS OVER THE NEXT 

SEVERAL DAYS.   



.SEAS...OVER THE N AND NE QUADRANTS OF HERMINE WAVE HEIGHTS ARE 

SEVERAL FT HIGHER THAN THE 12Z WW3 AND 12Z ECMWF WAM. HOWEVER 

BOTH SETS OF GUIDANCE APPEAR SOMEWHAT OVERDONE ACROSS THE SE 

QUADRANT THIS AFTERNOON. WILL USE THE SLIGHLTY HIGHER 00Z ECMWF 

WAM FOR WAVE HEIGHT GRIDS OVER THE NEAR TERM...BUT THIS FIELD 

WILL NEED SIGNIFICANT MANUAL ADJUSTMENTS. 



.EXTRATROPICAL STORM SURGE GUIDANCE...WITH MODELS FORECASTING 

HERMINE TO HAVE SUCH A SLOW MOTION OFF THE NRN MID ATLC AND SRN 

NEW ENGLAND COASTS THROUGH AT LEAST WED...THERE IS A HIGH 

LIKELIHOOD OF SIGNIFICANT AND POSSIBLY LIFE THREATENING STORM 

SURGE FROM THE DELMARVA PENINSULA TO THE SOUTHERN NEW ENGLAND 

COAST TODAY INTO NEXT WEEK. FOR FURTHER DETAILS AND GUIDANCE 

PLEASE SEE THE STORM SURGE SECTION OF THE NHC PUBLIC ADVISORY 

AND THE NHC PROTOTYPE STORM SURGE WATCH/WARNING GRAPHIC AT: 

WWW.HURRICANES.GOV/GRAPHICS_AT4.SHTML?WSURGE (ALL LOWERCASE). 

ALSO SEE THE NHC KEY MESSAGES CONCERNING STORM SURGE BELOW.



NHC KEY MESSAGES: 



1. THE SLOW MOTION AND LARGE WIND FIELD ASSOCIATED WITH HERMINE 

WILL RESULT IN A LONG DURATION OF HAZARDOUS CONDITIONS ALONG 

MUCH OF THE MID-ATLANTIC COAST EXTENDING INTO SOUTHERN NEW 

ENGLAND THROUGH THE HOLIDAY WEEKEND.



2. ALTHOUGH HERMINE HAS BECOME A POST-TROPICAL CYCLONE, NHC WILL

CONTINUE TO ISSUE ITS FULL SUITE OF ADVISORY AND WARNING 

PRODUCTS AS LONG AS THE SYSTEM REMAINS A SIGNIFICANT THREAT TO 

LAND AREAS.



3. P-SURGE, THE MODEL THAT DRIVES THE POTENTIAL STORM SURGE 

FLOODING GRAPHIC, IS DESIGNED FOR A WIND FIELD TYPICAL OF A 

TROPICAL CYCLONE.  THE WIND FIELD OF HERMINE IS VERY POORLY 

REPRESENTED BY THE P-SURGE MODEL AND AS A RESULT, RECENT 

FLOODING GRAPHICS HAVE UNDERSTATED THE INUNDATION RISK FROM THE 

CAROLINAS NORTHWARD.  NHC WILL BE DISCONTINUING RUNS OF THE 

P-SURGE MODEL FOR HERMINE WITH THIS ADVISORY.  THE NWS IS 

ATTEMPTING TO SUBSTITUTE THE GFS ENSEMBLE SYSTEM FOR P-SURGE FOR 

THE NEXT ISSUANCE OF THE POTENTIAL STORM SURGE FLOODING GRAPHIC, 

TO PROVIDE A MORE REALISTIC DEPICTION OF THE THREAT.  IF THIS 

EFFORT IS UNSUCCESSFUL, ISSUANCE OF THE POTENTIAL STORM SURGE 

FLOODING GRAPHIC FOR HERMINE WILL ALSO BE DISCONTINUED.



4. THE PROTOTYPE STORM SURGE WATCH/WARNING GRAPHIC DOES ACCOUNT 

FOR THE CURRENT WIND STRUCTURE OF HERMINE, AND THEREFORE 

ACCURATELY IDENTIFIES THOSE AREAS AT RISK FOR LIFE-THREATENING 

STORM SURGE. THIS GRAPHIC WILL CONTINUE TO BE PRODUCED FOR 

HERMINE.







.WARNINGS...PRELIMINARY.



.NT1 NEW ENGLAND WATERS...

.ANZ805...GEORGES BANK WEST OF 68W...

     TROPICAL STORM SUN INTO SUN NIGHT. 

     TROPICAL STORM POSSIBLE WED INTO THU NIGHT. 

.ANZ900...GEORGES BANK EAST OF 68W...

     TROPICAL STORM POSSIBLE WED NIGHT INTO THU NIGHT. 

.ANZ810...SOUTH OF NEW ENGLAND...

     TROPICAL STORM TONIGHT INTO MON. 

     TROPICAL STORM POSSIBLE MON NIGHT INTO THU. 

.ANZ815...SOUTH OF LONG ISLAND...

     TROPICAL STORM TONIGHT INTO MON. 

     TROPICAL STORM POSSIBLE MON NIGHT INTO WED NIGHT. 



.NT2 MID ATLC WATERS...

.ANZ820...HUDSON CANYON TO BALTIMORE CANYON...

     TROPICAL STORM TONIGHT INTO MON. 

     TROPICAL STORM POSSIBLE MON NIGHT INTO WED. 

.ANZ915...HUDSON CANYON TO THE GREAT SOUTH CHANNEL...

     TROPICAL STORM TONIGHT INTO SUN NIGHT. 

     HURRICANE MON.

     HURRICANE POSSIBLE MON NIGHT.

     TROPICAL STORM POSSIBLE TUE INTO THU. 

.ANZ920...BALTIMORE CANYON TO THE GREAT SOUTH CHANNEL...

     TROPICAL STORM TONIGHT INTO SUN. 

     HURRICANE SUN NIGHT INTO MON. 

     HURRICANE POSSIBLE MON NIGHT.

     TROPICAL STORM POSSIBLE TUE INTO WED NIGHT. 

.ANZ905...THE GREAT SOUTH CHANNEL TO THE HAGUE LINE...

     TROPICAL STORM TONIGHT INTO MON. 

     TROPICAL STORM POSSIBLE WED INTO THU NIGHT. 

.ANZ910...EAST OF THE GREAT SOUTH CHANNEL AND SOUTH OF 39N...

     TROPICAL STORM TONIGHT INTO MON. 

     TROPICAL STORM POSSIBLE WED INTO WED NIGHT. 

.ANZ825...INNER WATERS FROM BALTIMORE CANYON TO CAPE CHARLES LIGHT...

     TROPICAL STORM TONIGHT INTO MON. 

     TROPICAL STORM POSSIBLE MON NIGHT INTO TUE. 

.ANZ828...INNER WATERS FROM CAPE CHARLES LIGHT TO CURRITUCK BEACH LIGHT...

     TROPICAL STORM TONIGHT INTO MON. 

.ANZ925...OUTER WATERS FROM BALTIMORE CANYON TO HATTERAS CANYON...

     TROPICAL STORM TONIGHT INTO MON. 

     TROPICAL STORM POSSIBLE MON NIGHT INTO TUE. 

.ANZ830...INNER WATERS FROM CURRITUCK BEACH LIGHT TO CAPE HATTERAS...

     TROPICAL STORM TONIGHT INTO SUN. 

.ANZ930...OUTER WATERS FROM HATTERAS CANYON TO CAPE FEAR...

     TROPICAL STORM TONIGHT INTO SUN. 



$$



.FORECASTER MUSONDA/CLARK. OCEAN PREDICTION CENTER.

