326  
AGNT40 KWNM 240028  
MIMATN  
 
MARINE WEATHER DISCUSSION FOR N ATLANTIC OCEAN  
NWS OCEAN PREDICTION CENTER WASHINGTON DC  
828 PM EDT THU MAR 23 2017  
   
FORECAST DISCUSSION
 
MAJOR FEATURES/WINDS/SEAS/SIGNIFICANT  
.WEATHER FOR THE NORTH ATLANTIC OCEAN W OF 50W FROM 30N TO 50N.  
 
UPDATE...THE 18Z NCEP SURFACE ANALYSIS SHOWS A LARGE HIGH PRES  
RIDGE MOVING E OVER ALL OF THE COASTAL/OFFSHORE WATERS, AND A  
STRONG 994 MB LOW CENTERED OVER SRN NEWFOUNDLAND. LATEST  
AVAILABLE ASCAT HI-RES AND ASCAT PASSES FROM THIS MORNING SHOW 25  
TO 35 KT WINDS IN NW FLOW OVER THE GEORGES BANK ZONES AND THE NE  
PART OF THE NT2 WATERS IN THE TIGHT PRES GRADIENT BETWEEN THE  
LOW AND THE RIDGE, AND 20 TO 25 KT WINDS IN NE FLOW ACROSS THE SW  
PART OF THE NT2 AREA.  
 
MODELS...THE MEDIUM RANGE MODELS ARE IN GOOD OVERALL AGREEMENT  
ACROSS THE OFFSHORE WATERS FOR TONIGHT INTO FRI, SO THE GFS 10M  
SOLUTION WILL BE USED FOR THE WIND GRIDS OVER THIS TIMEFRAME. THE  
GFS CONTINUES TO LOOK OVERDONE WITH THE STRENGTH OF THE SW FLOW  
OVER THE NT1 AND NRN NT2 WATERS FOR LATER FRI AND FRI NIGHT, AND  
THE GFS IS ALSO FASTER THAN MOST OF THE OTHER MODELS FOR MON AND  
MON NIGHT. THUS, THE MORE REPRESENTATIVE ECMWF WILL BE USED FOR  
LATER FRI THROUGH MON NIGHT. THE MODELS ARE IN POOR AGREEMENT  
REGARDING THE TIMING AND TRAJECTORY OF A LOW WHICH IS EXPECTED TO  
MOVE OFF THE MID ATLANTIC COAST TUE INTO TUE NIGHT, BUT SINCE THE  
GFS LOOKS LIKE THE BEST MEDIAN MODEL SOLUTION, IT WILL BE USED  
FOR TUE THROUGH THE REST OF THE FORECAST PERIOD.  
 
SEAS...THE WNA WAVEWATCH INITIALIZED 2 TO 4 FEET TOO LOW OVER THE  
GULF OF MAINE AND GEORGES BANK WATERS, SO THE MORE ROBUST ECMWF  
WAM IS PREFERRED FOR TONIGHT. THE WAVEWATCH/WAM ARE IN DECENT  
AGREEMENT OVER THE OFFSHORE WATERS FOR FRI THROUGH MON NIGHT WITH  
ONLY MINOR DIFFERENCES NOTED, SO A 50/50 BLEND OF THESE MODELS  
WILL BE USED FOR THE SEA HEIGHT GRIDS DURING THAT TIMEFRAME. A  
SOMEWHAT MODIFIED/CAPPED WNA WAVEWATCH WILL BE USED EXCLUSIVELY  
FOR TUE THROUGH THE REST OF THE FORECAST PERIOD, IN ORDER TO BE  
CONSISTENT WITH THE PREFERRED GFS MODEL.  
 
EXTRATROPICAL STORM SURGE GUIDANCE...N/A.  
 
-----------------------------------------------------------------  
PREVIOUS DISCUSSION...  
 
THERE WAS AN ASCAT PASS AT ABOUT 1445Z WITH A SWATH ACROSS THE  
FAR ERN WATERS OF GEORGES BANK AND INTO THE FAR ERN WATERS OF THE  
NRN MID ATLANTIC WATERS. WINDS WERE AT BIT STRONGER THAN GRID  
VALUES IN THIS REGION WITH 35 KT WHILE WE HAD 30 KT IN THIS AREA.  
THERE WAS A SHIP OBSERVATION JUST W OF THIS AREA WHICH HAD 25 KT  
ALTHOUGH COULD NOT FIND ANY QC HISTORY WITH THIS OBSERVATION. IN  
ANY CASE THE AREA OF GALES SHOULD HAVE MOVED E OF THE WATERS  
SEVERAL HOURS AGO.  
 
IN THE EARLY AFTERNOON AT 18Z HIGH PRESSURE WAS CENTERED OVER THE  
DELMARVA PENINSULA AND WILL BE MOVING E INTO THE OFFSHORE WATERS  
THROUGH TONIGHT AND FRIDAY. THE CENTER OF HIGH PRESSURE MOVES E  
OF THE OFFSHORE WATERS BY FRIDAY AFTERNOON WHILE BECOMING WEAKER.  
WITH REGARDS TO WINDS OVER THE OFFSHORE WATERS WINDS BECOME  
LIGHT AT 15 KT OR LESS THROUGHOUT MOST OF THE REGION BY 8 AM  
FRIDAY. BY LATE FRIDAY A WARM FRONT WILL MOVE NE TOWARDS THE WRN  
NEW ENGLAND WATERS. GEM/UKMET/GFS ARE CONSISTENT WITH HAVING  
WINDS TO 30 KT BY LATE FRIDAY WITH THE APPROACHING WARM FRONT.  
MODELS ARE CONSISTENT WITH LOW PRESSURE DEVELOPING N OF THE NEW  
ENGLAND WATERS FRIDAY NIGHT AND STRENGTHENING WHILE PASSING E OF  
THE WATERS. ASSOCIATED COLD FRONT MOVES S OVER THE NEW ENGLAND  
WATERS LATE FRIDAY NIGHT INTO SATURDAY...THEN CROSSING INTO THE  
NRN MID ATLANTIC WATERS LATER ON SATURDAY BEFORE STALLING OVER  
THE NRN MID ATLANTIC THROUGH ABOUT SUNDAY NIGHT. MODELS ARE  
SIMILAR WITH HIGH PRESSURE BUILDING IN FROM THE NW OVER THE NEW  
ENGLAND WATERS LATE SATURDAY INTO SATURDAY NIGHT...THEN SETTLING  
ACROSS THE AREA SUNDAY...BEFORE PASSING E OF THE NEW ENGLAND  
WATERS SUNDAY NIGHT AND MONDAY. BY MONDAY AN UPPER SHORTWAVE WILL  
MOVE ACROSS THE PA/NY STATE AND THEN E INTO THE OFFSHORE WATERS  
LATE MONDAY AND MONDAY NIGHT WHILE BECOMING WEAKER. AS THIS  
OCCURS THE STALLED FRONT MOVES BACK TO THE N OVER THE NEW ENGLAND  
WATERS WITH WEAK LOW PRESSURE DISSIPATING AS IT MOVES E INTO THE  
WATERS BY EARLY TUESDAY. BY LATE TUESDAY AND TUESDAY NIGHT MODELS  
DIVERGE WITH LOW PRESSURE THAT APPROACHES AND CROSSES INTO THE  
WATERS. PREFER THE GFS WHICH IS SLOWER THAN THE ECMWF WITH  
MOVING THE LOW PRESSURE INTO THE WATERS. THERE IS SOME AGREEMENT  
FROM THE UKMET ON A SLOWER SOLUTION. ALSO THE WEATHER PREDICTION  
CENTER HAS ACCEPTED THE IDEA OF THE SLOWER PROGRESS OF LOW  
PRESSURE MOVING E INTO THE WATERS.  
 
FOR THE GRIDS PLAN TO FAVOR THE GFS INITIALLY THROUGH EARLY  
FRIDAY...THEN USE THE ECMWF THROUGH ABOUT MONDAY NIGHT...THEN  
USE GFS FROM EARLY TUESDAY INTO TUESDAY NIGHT. THE GFS SEEMS  
OVERLY STRONG WITH ELY WINDS BY LATE TUESDAY AND TUESDAY NIGHT OVER  
THE NEW ENGLAND WATERS...AND WILL LIMITS WINDS SINCE NO OTHER  
GUIDANCE IS AS STRONG WITH WINDS OVER THE NRN NEW ENGLAND WATERS.  
 
SEAS...FOR SEAS EARLIER OBSERVATIONS FROM 14 AND 15Z JUST ALONG  
AND E OF THE NEW ENGLAND WATERS SHOWED 17 FT WITH BUOY 44011 AND  
20 FT WITH BUOY 44024. THESE OBSERVATIONS WERE MUCH BETTER  
DEPICTED BY THE ECMWF WAM OVER THE . OVER GEORGES BANK THE ECMWF  
WAM MATCHED WITH THE ECMWF WAM...BUT WAS ABOUT 3 TO 4 FT LOWER  
JUST E OF THE NEW ENGLAND WATERS WITH THE 20 FT SEAS. BY  
COMPARISON THE WWIII WAS ABOUT 4 FT TOO LOW WITH 44011 AND ABOUT  
8 FT TOO LOW WITH BUOY 44024. WILL USE THE ECMWF WAM ACROSS THE  
OFFSHORE FOR TONIGHT....THEN USE A 50/50 BLEND OF THE WWIII AND  
ECMWF WAM FROM FRIDAY INTO MONDAY...THEN USE THE WWIII ALTHOUGH  
WILL CUT SEAS DOWN BY LATE TUESDAY WITH SEAS SEEMING TOO HIGH  
OVER THE NEW ENGLAND WATERS.  
   
EXTRATROPICAL STORM SURGE GUIDANCE
 
N/A.  
   
WARNINGS
 
PRELIMINARY.  
   
NT1 NEW ENGLAND WATERS
 
 
NONE.  
   
NT2 MID-ATLANTIC WATERS
 
 
NONE.  
 

 
 
.FORECASTER SCOVIL/ROWLAND. OCEAN PREDICTION CENTER.  
 
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