678  
AGNT40 KWNM 221149  
MIMATN  
 
MARINE WEATHER DISCUSSION FOR N ATLANTIC OCEAN  
NWS OCEAN PREDICTION CENTER WASHINGTON DC  
749 AM EDT SAT JUL 22 2017  
   
FORECAST DISCUSSION
 
MAJOR FEATURES/WINDS/SEAS/SIGNIFICANT  
.WEATHER FOR THE NORTH ATLANTIC OCEAN W OF 50W FROM 30N TO 50N.  
 
A STATIONARY FRONT W TO E ACROSS THE SOUTHERN NT1 WATERS  
SEPARATES A WEAK NNW GRADIENT (GENERALLY 10-15 KT OR LESS) TO ITS  
N, AND A SLIGHTLY STRONGER SWLY GRADIENT (GENERALLY 10-20 KT) TO  
ITS S. MAX SEAS THROUGHOUT THE WATERS ARE IN THE 4-6 FT RANGE AT  
THE MOMENT, HIGHEST ACROSS THE OUTERMOST CENTRAL NT2 WATERS, AND  
ARE BEING HANDLED FINE BY THE 06Z WAVEWATCH III AND 00Z ECMWF WAM  
MODELS.  
 
OVER THE SHORT TERM, IN GENERAL THE LATEST MODELS AGREE THAT THE  
FRONT WILL REMAIN QUASI-STATIONARY TODAY THROUGH MON NIGHT. BUT,  
AT THE SAME TIME THE MODELS HAVE BOTH TIMING AND FORECAST  
STRENGTH DIFFERENCES IN REGARDS TO A SERIES OF SURFACE LOWS  
FORECAST TO TRACK E ALONG THE FRONT. DUE TO THE EXPECTED SHORT  
WAVE LENGTH BETWEEN THESE FRONTAL LOWS, DO NOT HAVE A  
PARTICULARLY HIGH LEVEL OF FORECAST CONFIDENCE IN THE FORECAST  
SOLUTION OF ANY INDIVIDUAL MODEL. BUT, OVERALL SINCE THEY ARE IN  
REASONABLY GOOD AGREEMENT IN REGARDS TO THEIR FORECAST POSITIONS  
OF THE FRONT, FOR NOW WOULD FAVOR A COMPROMISE 06Z/00Z GFS AND  
00Z ECMWF SOLUTION FOR THE SHORT TERM. SO PLAN ON CONTINUING TO  
USE THE PREVIOUSLY POPULATED MIX OF GFS AND ECMWF WINDS THROUGH  
MON NIGHT WITH SOME MINOR ADDITIONAL EDITS IN DEFERENCE TO THE  
06Z GFS.  
 
IN THE LONG RANGE, SINCE ITS GENERALLY SUPPORTED BY THE 06Z/00Z  
GFS AND IN LINE WITH THE LATEST WPC MEDIUM RANGE GUIDANCE, WILL  
CONTINUE TO FAVOR THE 00Z ECMWF SOLUTION OF A FINAL FRONTAL LOW  
PASSING E OF THE NT1 WATERS TUE/TUE NIGHT AND PULLING THE FRONT S  
AS A COLD FRONT ACROSS THE N/CENTRAL NT2 WATERS, FOLLOWED THEN BY  
THE FRONT STALLING ACROSS THE CENTRAL NT2 WATERS WED/WED NIGHT  
WITH ITS ASSOCIATED GRADIENTS WEAKENING. SO PLAN ON MAKING  
MINIMAL LONG RANGE CHANGES TO THE PREVIOUS OFFSHORE FORECAST  
PACKAGE.  
 
-----------------------------------------------------------------  
PREVIOUS DISCUSSION...  
 
SUMMARY...THE 00Z NCEP SURFACE ANALYSIS SHOWS A STATIONARY FRONT  
EXTENDING NE TO SW ALONG THE MAINE COAST, WITH A LOW PRES TROUGH  
EXTENDING NE OVER SOUTHERN NEW ENGLAND AND INTO THE GULF OF  
MAINE. THE ANALYSIS ALSO INDICATES A HIGH PRESSURE RIDGE OVER  
THE NT2 WATERS. LATEST AVAILABLE ASCAT AND ASCAT HI-RES PASSES  
FROM A FEW HOURS AGO SHOW WINDS TO 20 KT IN W TO SW FLOW OVER  
THE CENTRAL NT2 WATERS, WITH 5 TO 15 KT WINDS INDICATED ACROSS  
THE REMAINDER OF THE OFFSHORE WATERS.  
 
MODELS...THE 00Z MEDIUM RANGE MODELS ARE IN VERY GOOD OVERALL  
AGREEMENT ACROSS THE OFFSHORE WATERS FOR TODAY INTO EARLY SUN,  
SO THE REPRESENTATIVE 00Z GFS 10M SOLUTION WILL BE USED FOR THE  
WIND GRIDS OVER THIS TIMEFRAME. THERE ARE SOME TIMING AND  
TRAJECTORY DIFFERENCES AMONG THE MODELS REGARDING SEVERAL LOW  
PRES SYSTEMS THAT ARE EXPECTED TO PASS E ACROSS THE OFFSHORE  
WATERS NEAR 40N ON SUN INTO MON. IN ORDER TO RESOLVE THESE  
DIFFERENCES, WILL USE A 50/50 BLEND OF THE 00Z ECMWF/GFS 10M FOR  
LATER SUN INTO MON. THE 00Z ECWMF WILL BE USED EXCLUSIVELY FOR  
LATE MON THROUGH THE REST OF THE FORECAST PERIOD, BECAUSE IT HAS  
HAD THE BEST RUN TO RUN CONSISTENCY OF ALL OF THE MODELS AND ALSO  
SINCE IT HAS VERY GOOD SUPPORT FROM THE LATEST WPC MEDIUM RANGE  
FORECASTER GUIDANCE.  
 
SEAS...THE 00Z WNA WAVEWATCH AND 00Z ECMWF WAM BOTH INITIALIZED  
WELL OVER THE OFFSHORE WATERS. THE MODELS ARE IN GOOD OVERALL  
AGREEMENT FOR TODAY INTO MON WITH ONLY MINOR DIFFERENCES NOTED,  
SO WILL USE A 50/50 BLEND OF THE 00Z WNA WAVEWATCH/ECMWF WAM FOR  
THIS TIMEFRAME TO SMOOTH OUT THE MODEL DIFFERENCES. THE 00Z ECMWF  
WAM WILL BE USED EXCLUSIVELY FOR THE SEA HEIGHT GRIDS FOR LATE  
MON THROUGH WED NIGHT, IN ORDER TO BE CONSISTENT WITH THE  
PREFERRED 00Z ECMWF MODEL OVER THIS TIMEFRAME.  
   
EXTRATROPICAL STORM SURGE GUIDANCE
 
N/A.  
 
   
WARNINGS
 
PRELIMINARY.  
   
NT1 NEW ENGLAND WATERS
 
 
NONE.  
   
NT2 MID-ATLANTIC WATERS
 
 
NONE.  
 

 
 
.FORECASTER VUKITS/SCOVIL. OCEAN PREDICTION CENTER.  
 
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