

395 

AGNT40 KWNM 041325

MIMATN



MARINE WEATHER DISCUSSION FOR N ATLANTIC OCEAN 

NWS OCEAN PREDICTION CENTER WASHINGTON DC

826 AM EDT SUN 4 SEP 2016 



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

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



HERMINE HAS MOVED FAR ENOUGH EASTWARD THAT ITS HIGHEST WINDS ARE 

ALSO EAST OF THE MID ATLC BUOYS. A 02Z ASCAT PASS RETURNED 50 TO 

55 KT ACROSS THE GULF STREAM FROM ABOUT 36.5N TO 38N...JUST NW 

OF THE OCCLUDED FRONT. WITH HERMINE FORECAST TO SLOWLY MEANDER 

ENE TODAY INTO TONIGHT THE STRONGEST N TO NE WINDS WILL CONTINUE 

TO BE COUNTERFLOW TO THE GULF STREAM CREATING A PERILOUS SEA 

STATE. LATEST HRRR SEEMS TO HAVE AN EXCELLENT HANDLE ON THE NEAR 

TERM WINDS...AND IS SUPPORTED BY REMAINING GUIDANCE IN 

INDICATING WINDS SHOULD STRENGTHEN TO HURCN FORCE LATER TODAY 

THROUGH MON. THEN OVER THE PAST DAY OR SO MODELS HAVE GENERALLY 

TRENDED WEAKER WITH HERMINE TUE THROUGH THE THU NIGHT. THERE 

CONTINUES TO BE SIGNIFICANT MODEL DISCREPANCY WITH THE TIMING 

THE WEAKENING UPPER LOW EJECTING NE OF GEORGES BANK LATER IN THE 

WEEK. AS WAS THE CASE WITH YESTERDAYS RUNS THE 00Z ECMWF REMAINS 

MUCH MORE PROGRESSIVE THAN THE GFS OR UKMET. THE 06Z GFS OFFERS 

A COMPROMISE BETWEEN THE 00Z ECMWF AND 00Z UKMET...AND THE LAST 

NHC ADVISORY SEEMED TO RELY MOSTLY ON THE GFS. AS FAR AS 

WARNINGS AM NOT ANTICIPATING THAT THERE WILL BE MUCH CHANGE FROM 

PREVIOUS NT1/NT2 FORECASTS. WARNINGS GIVEN IN SUMMARY SECTION 

BELOW ARE BASED ON THE 09Z NHC ADVISORY.  



GIVEN LAST EVENINGS ASCAT WITH PLACEMENT OF THE 50 TO 55 KT 

WINDS ACROSS THE GULF STREAM WE BELIEVE THE HIGHER ECMWF WAM HAS 

A MUCH BETTER HANDLE THAN THE WAVEWATCH III ON THE OFFSHORE WAVE 

HEIGHTS THIS MORNING. IN FACT EVEN THE ECMWF WAM MAY BE SLIGHTLY 

LOW WITH A MAX OF 26 FT SHOWN AT 12Z THIS MORNING. THE NHC TRACK 

FORECAST IS QUITE DIFFERENT FROM THE ECMWF THOUGH SO BEGINNING 

TONIGHT TRANSITIONED BACK TO THE WAVEWATCH FOR WAVE HEIGHT 

GRIDS...BUT BUMPED UP SEAS GREATER THAN 10 FT OR SO BY ABOUT 20 

TO 25 PERCENT.  



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

...PREVIOUS DISCUSSION...



THE SAT IMG INDC POST-TROPICAL CYCLONE HERMINE OVER THE CENTRAL 

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

INCLUDING THE ASCAT PASS AT 0250Z HAVE HIGHER WINDS OVER THE 

CENTRAL WATERS. BUOY 44014 IN VIRGINIA BEACH IN THE PAST FEW 

HOURS HAD WINDS 30 TO 35 KT AND GUSTS TO 40 KT WITH PEAK SEAS AT 

15 FT SEAS. AT 06Z THE NCEP MAP HAS POST-TROPICAL CYCLONE 

HERMINE OVER THE CENTRAL WATERS AND WEAK HIGH PRES WITH CENTERS 

INLAND W AND NW OF HERMINE AND 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. 



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 HERMINE OVER THE WATERS. IN THE 

EXTENDED PERIOD THE UPPERLEVEL RIDGE TO THE E OF THE WATER WILL 

BLOCK THE ENRGY FROM ADVANCING E AND THAT SHOULD KEEP THE ENERGY 

TRAPPED IN THE CLOSED LOW LONGER OVER THE WATERS. THE RIDGE TO 

THE E WILL WEAKEN AND ALLOW THE ENERGY TO SLIDE NE. 



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

WITH THE 06Z OBERVATIONS WITH JUST VERY MINOR DIFFERENCES IN THE 

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

LARGER AREA OF WINDS IN THE WARNING RANGE. THE MODELS ALSO HAVE 

SOME DIFFERENCES ON THE TRACK OF THE STORM AND THESE DIFFERENCES 

ARE EVEN GREATER WHEN THE MOVEMENT OF STROM SLOWS DOWN BETWEEN 

05/1200Z AND 07/0000Z. I DID NOT HAVE THE LATEST RUN OF NOGAPS 

BUT THE MODEL STILL AGREE WITH THE REST IN KEEPING THE STORM 

OVER THE CENTRAL WATERS. INITIALLY THE ECMWFHR IS MORE 

PROGRESSIVE WITH THE SYSTEM AND IT TRIES TO KEEP IT E OF THE 

OTHER MODELS. GFS ALSO KEEPS STORM W OF THE OTHER MODELS. 

HOWEVER...THE MODELS SHOWED A SLIGHTLY BETTER AGREEMENT AFTER 

07/0000Z AS THE SYSTEM SHOW SIGNS OF MOVING NE. STILL TRICKY TO 

STICK TO ONE MODEL SOLUTION AND SO WILL CONTINUE TO FOLLOW THE 

NHC TRACK OF HERMINE. WILL USE GFS AND THE ECMWFHR BACK TO BACK 

AND MAKE ADJUSTMENTS TO THE WINDS ACCORDINGLY. IN THE SHORT TERM 

HERMINE WILL PERSIST OVER THE CENTRAL WATERS BUT WILL START TO 

MOVE NE IN THE EXTENDED PERIOD. A RIDGE OF HIGH PRES WILL THEN 

MOVE INTO THE REGION. 



.SEAS...THE HIGHEST SEAS ARE STILL 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 WITH THE 

OBSERVED SEAS PATTERN BUT JUST UNDERDONE BY 2 FT FOR THE PEAK 

VALUE. THE ECMWFWAVE HAS ALSO INITIALIZED WELL BUT ALSO 

UNDERDONE BY JUST 1 FT WITH THE PEAK VALUE. THE OFFICIAL TRACK 

OF THE STORM MAY HAVE SHIFTED SLIGHTLY E FROM THE PREVOIUS TRACK 

BUT THE SEAS HAVE NOT SIGNIFICANTLY CHANGED AND SO WILL TRY TO 

STAY WITH NWW3 BUT MAKE SOME ADJUSTMENTS ESPECIALLY OVER THE ERN 

PARTS. 



.EXTRATROPICAL STORM SURGE GUIDANCE...WITH MODELS FORECASTING 

HERMINE TO HAVE A SLOW MEANDERING MOTION OFF THE NRN MID ATLC 

AND SRN NEW ENGLAND COASTS THROUGH AT LEAST WED...STORM SURGE 

WILL CONTINUE TO IMPACT THE COAST FROM THE DELMARVA PENINSULA TO 

THE SOUTHERN NEW ENGLAND COAST INTO THIS 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 AND INTO MIDWEEK.



2. SMALL CHANGES IN THE MEANDERING TRACK OF HERMINE COULD RESULT 

IN LARGE DIFFERENCES IN THE IMPACTS ALONG THE MID-ATLANTIC COAST 

DURING THE NEXT SEVERAL DAYS.  IN ADDITION, THERE COULD BE 

MULTIPLE OCCURRENCES OF TROPICAL STORM CONDITIONS IN SOME 

LOCATIONS WITHIN THE WARNING AREA DURING THIS TIME.



3. 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.



4. 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, FLOODING 

GRAPHICS PRIOR TO TODAY'S 11 AM EDT ADVISORY UNDERSTATED THE 

INUNDATION RISK FROM THE CAROLINAS NORTHWARD.  THE NWS IS USING 

THE GFS ENSEMBLE SYSTEM INSTEAD OF P-SURGE FOR ONGOING ISSUANCES 

OF THE POTENTIAL STORM SURGE FLOODING GRAPHIC TO PROVIDE A MORE 

REALISTIC DEPICTION OF THE THREAT.



5. THE PROTOTYPE STORM SURGE WATCH/WARNING GRAPHIC ACCOUNTS FOR

THE CURRENT WIND STRUCTURE OF HERMINE, AND THEREFORE ACCURATELY

IDENTIFIES THOSE AREAS AT RISK FOR LIFE-THREATENING STORM SURGE.

THIS GRAPHIC WILL ALSO CONTINUE TO BE PRODUCED FOR HERMINE.



.WARNINGS...PRELIMINARY.



.NT1 NEW ENGLAND WATERS...

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

     TROPICAL STORM TODAY INTO MON NIGHT. 

     TROPICAL STORM POSSIBLE TUE INTO THU. 

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

     TROPICAL STORM TODAY INTO TONIGHT. 

     TROPICAL STORM POSSIBLE WED INTO THU NIGHT. 

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

     TROPICAL STORM TODAY INTO MON NIGHT. 

     TROPICAL STORM POSSIBLE TUE INTO WED NIGHT. 

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

     TROPICAL STORM TODAY INTO MON NIGHT. 

     TROPICAL STORM POSSIBLE TUE INTO WED. 



.NT2 MID ATLC WATERS...

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

     TROPICAL STORM TODAY INTO MON NIGHT. 

     TROPICAL STORM POSSIBLE TUE INTO TUE NIGHT. 

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

     TROPICAL STORM TODAY INTO TONIGHT. 

     HURRICANE MON INTO MON NIGHT. 

     HURRICANE POSSIBLE TUE.

     TROPICAL STORM POSSIBLE TUE NIGHT INTO WED NIGHT. 

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

     TROPICAL STORM TODAY INTO TONIGHT. 

     HURRICANE MON INTO MON NIGHT. 

     HURRICANE POSSIBLE TUE.

     TROPICAL STORM POSSIBLE TUE NIGHT INTO WED. 

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

     TROPICAL STORM TODAY INTO MON NIGHT. 

     TROPICAL STORM POSSIBLE TUE INTO THU NIGHT. 

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

     TROPICAL STORM TODAY INTO MON NIGHT. 

     TROPICAL STORM POSSIBLE TUE INTO WED NIGHT. 

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

LIGHT...

     TROPICAL STORM TONIGHT INTO MON NIGHT. 

.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 TODAY INTO MON NIGHT. 

     TROPICAL STORM POSSIBLE TUE.



$$ 



.FORECASTER CLARK/MUSONDA. OCEAN PREDICTION CENTER.

