917  
AGNT40 KWNM 190726  
MIMATN  
 
MARINE WEATHER DISCUSSION FOR N ATLANTIC OCEAN  
NWS OCEAN PREDICTION CENTER WASHINGTON DC  
226 AM EST MON FEB 19 2018  
   
FORECAST DISCUSSION
 
MAJOR FEATURES/WINDS/SEAS/SIGNIFICANT  
.WEATHER FOR THE NORTH ATLANTIC OCEAN W OF 50W FROM 30N TO 50N.  
 
THE LATEST GOES INFRARED SATELLITE IMAGERY INDICATES AN INTENSE  
HURRICANE FORCE LOW PRESSURE SYSTEM WELL E OF THE OFFSHORE  
WATERS THIS MORNING, AND COLD CUMULUS EXTENDING TO THE W INTO  
THE OUTER NT2 AND FAR SE NT1 OFFSHORE WATERS IN THE REMAINING  
COLD ADVECTION. ASCAT WIND RETRIEVALS FROM 01Z LAST NIGHT  
INDICATED A FEW 20 KT BARBS IN THE REMAINING COLD ADVECTION, AND  
CURRENT SURFACE OBSERVATIONS INDICATE NO MORE THAN 15 TO 20 KT IN  
THE OFFSHORE WATERS AT 0600 UTC WITH HIGH PRES BUILDING OVER THE  
W ATLC. THE 00Z GFS AND ECMWF WINDS ARE INITIALIZED WELL WHEN  
COMPARED WITH THE DATA, AND THE MODELS INDICATE THAT THE WINDS  
WILL REMAIN LIGHT THIS MORNING WITH THE HIGH PRES OVER THE AREA.  
THE 00Z GFS AND ECMWF THEN INDICATE A WEAK COLD FRONT WILL  
APPROACH THE NEW ENGLAND COAST THIS AFTERNOON INTO TONIGHT,  
BEFORE THE WEAK BOUNDARY MOVES OFFSHORE LATE TONIGHT INTO TUE.  
THE GFS IS A LITTLE STRONGER THAN THE ECMWF WITH THE SW WINDS  
AHEAD OF THE FRONT, AND INDICATES UP TO 30 KT IN THE WARM  
ADVECTION OVER THE COLD SSTS IN THE GULF OF MAINE. THE 00Z ECMWF  
ONLY INDICATES 25 KT, AND SEEMS A BIT MORE REASONABLE WHEN  
CONSIDERING THE STABLE BOUNDARY LAYER OVER THE COLD WATERS IN  
NT1. AS A COMPROMISE, AM PLANNING ON STARTING OUT WITH A 50/50  
BLEND OF THE GFS AND ECMWF, WHICH SHOULD ACT TO SLIGHTLY INCREASE  
THE AREAL COVERAGE OF 25 KT WINDS.  
 
THE MODELS REMAIN IN DECENT AGREEMENT THROUGH THE SHORT RANGE  
INTO THU NIGHT, AND INDICATE A SLIGHTLY STRONGER FRONT WILL  
APPROACH NT1 WED BEFORE MOVING OFFSHORE WED NIGHT. THE GFS AND  
ECMWF REMAIN IN DECENT AGREEMENT ON THE TIMING OF THE FRONT,  
THOUGH THE GFS AGAIN BECOMES A BIT STRONGER WITH THE WINDS AHEAD  
OF THE FRONT. THE MODELS THEN INDICATE THAT THE FRONT WILL  
CONTINUE SE THROUGH THE OFFSHORE WATERS BEFORE STALLING OVER NRN  
NT2 BY LATE THU AS ANOTHER HIGH BUILDS OVER NEW ENGLAND. THE 00Z  
ECMWF SEEMS A LITTLE TOO WEAK WITH THE NE FLOW BEHIND THE FRONT,  
WHILE THE GFS IS A BIT STRONGER. AS A COMPROMISE, AM PLANNING ON  
CONTINUING PREVIOUS 50/50 BLEND THROUGH THU NIGHT. THE 00Z ECMWF  
THEN INDICATES ANOTHER FRONT WILL PASS THROUGH THE REGION ON SAT,  
THOUGH IS FASTER THAN THE 00Z GFS. THE 00Z UKMET IS ABOUT 6 HOURS  
SLOWER THAN THE 00Z ECMWF, AND IS NEAR THE TIMING OF THE WPC  
MEDIUM RANGE GUIDANCE. AS A COMPROMISE TO THE TIMING DIFFERENCES,  
AM PLANNING ON USING THE 00Z ECMWF FROM FRI 12Z ONWARD. HOWEVER,  
WILL TIME SHIFT THE MODEL 6 HOURS SLOWER TO MATCH UP BETTER WITH  
THE 00Z UKMET AND THE WPC MEDIUM RANGE GUIDANCE.  
 
SEAS...THE 00Z ECMWF WAM AND WAVEWATCH ARE INITIALIZED WITHIN A  
FT OR TWO OF THE CURRENT DATA, AND ARE IN GOOD AGREEMENT INTO 12Z  
FRI. AS A RESULT, PLANNING ON STARTING OUT WITH A 50/50 BLEND OF  
THE TWO MODELS AS A COMPROMISE. WILL THEN TRANSITION SOLELY TO  
THE 00Z ECMWF WAM AFTER 12Z FRI, BUT WILL USE THE SAME 6 HOUR  
TIME SHIFT AS USED WITH THE 00Z ECMWF WINDS TO SLOW DOWN THE  
PROGRESSION OF SEAS ASSOCIATED WITH THE FRONT ON SAT.  
 
EXTRATROPICAL STORM SURGE GUIDANCE...N/A.  
   
WARNINGS
 
PRELIMINARY.  
   
NT1 NEW ENGLAND WATERS
 
 
NONE.  
   
NT2 MID-ATLANTIC WATERS
 
 
NONE.  
 

 
 
.FORECASTER KELLS. OCEAN PREDICTION CENTER.  
 
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