262  
AGNT40 KWNM 151352  
MIMATN  
 
MARINE WEATHER DISCUSSION FOR N ATLANTIC OCEAN  
NWS OCEAN PREDICTION CENTER WASHINGTON DC  
952 AM EDT MON OCT 15 2018  
   
FORECAST DISCUSSION
 
MAJOR FEATURES/WINDS/SEAS/SIGNIFICANT  
.WEATHER FOR THE NORTH ATLANTIC OCEAN W OF 50W FROM 30N TO 50N.  
 
HIGH PRESSURE IS CENTERED EAST OF THE NORTHERN NT2 WATERS THIS  
MORNING WITH A RIDGE AXIS EXTENDING ACROSS THE NT2 ZONES. AS A  
RESULT, OFFSHORE WIND SPEEDS REMAIN LESS THAN 25 KT ACROSS THE  
REGION. HOWEVER, CONDITIONS WILL RAPIDLY DETERIORATE LATER TODAY  
AND TONIGHT AS A STRONG COLD FRONT MOVES OFF THE NEW ENGLAND AND  
NORTHERN MID-ATLANTIC COAST. THE 06Z NAM NEST WINDS SUPPORT OUR  
CURRENT FORECAST WITH WINDS STRENGTHENING TO GALE FORCE AHEAD OF  
THE FRONT OVERNIGHT ACROSS PORTIONS OF THE NT1 AND NORTHERN NT2  
WATERS. POST-FRONTAL GALES WILL LIKELY PERSIST INTO EARLY TUE  
BEFORE THE SYSTEM CLEARS THE REGION. WITH NO CHANGES TO OUR  
FORECAST REASONING OVER THE NEXT COUPLE DAYS, GRID EDITS WERE  
MINIMAL WITH THIS UPDATE. THIS SYSTEM IS JUST ONE OF A SERIES OF  
COLD FRONTS THAT WILL IMPACT OUR AREA THROUGHOUT THE FORECAST  
PERIOD, SO FURTHER CHANGES TO THE EXTENDED FORECAST MAY BE  
NECESSARY LATER TODAY AFTER EVALUATING THE 12Z GUIDANCE.  
 
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PREVIOUS DISCUSSION...  
 
A SERIES OF STRONG COLD FRONTS WILL PASS SE OVER THE WATERS  
DURING THE NEXT SEVERAL DAYS. THE FIRST STRONG FRONT WILL IMPACT  
CONDITIONS TONIGHT INTO TUE, THE SECOND LATER WED INTO THU, WITH  
A THIRD STRONG FRONT APPROACHING THE WATERS LATER FRI AND FRI  
NIGHT. THE BEST CHANCE FOR GALES IS EXPECTED WITH THE FIRST TWO  
FRONTS, WITH A LOWER CHANCE FOR GALES LATER IN THE WEEK WITH THE  
THIRD FRONT.  
 
OVER THE SHORT TERM, A LATE EVENING ASCAT OVERPASS INDICATED  
WINDS UP TO 15 KT OR SO MAINLY OVER THE FAR SOUTHERN OFFSHORE  
AND NORTHEASTERN OFFSHORE WATERS AS HIGH PRESSURE BUILDS E OVER  
THE REGION. THE FIRST STRONG COLD FRONT WILL APPROACH FROM THE W  
DURING THE DAY TODAY AS THE HIGH MOVES OFF TO THE E OF THE AREA.  
THE FRONT WILL CROSS THE WATERS TONIGHT INTO TUE, AND THEN STALL  
OFF THE NORTH CAROLINA COAST LATER TUE. A WEAK HIGH PRESSURE  
RIDGE WILL PASS E OVER WATERS N OF THE STALLED FRONT LATER TUE,  
WITH A WEAKENING RIDGE OVER THE FAR SOUTHERN WATERS. THERE  
APPEARS TO BE AN INCREASING THREAT FOR WIDESPREAD GALES BOTH IN  
ADVANCE OF, AND IN THE WAKE OF THE STRONG COLD FRONT. FOR THE  
EARLY MORNING PACKAGE, WE WILL RELY ON GUIDANCE FROM THE HIGH  
RESOLUTION 00Z WARW MODEL OUTPUT, EXCEPT WE WILL CAP WINDS AT 35  
KT AHEAD OF THE FRONT AS THE MODEL ATTEMPTS TO PLACE WINDS WELL  
ABOVE 35 KT IN PATCHY AREAS, AND THESE HIGHER WINDS ARE LIKELY  
ASSOCIATED WITH THUNDERSTORMS THAT WILL LIKELY FORM NEAR AND IN  
ADVANCE OF THE STRONG COLD FRONT. FOR THE EARLY MORNING PACKAGE  
WE WILL GO AHEAD AND ADD GALES TO ALL OF THE NEW ENGLAND WATERS,  
AND TO THE NORTHERN MID-ATLANTIC OFFSHORE WATERS AS WELL, OR ALL  
OF THE NORTHERN NT2 WATERS, FOR TONIGHT INTO TUE, AS STRONG 925  
MB WINDS OF 50 TO 65 KT DEVELOP AND SPREAD ACROSS THESE WATERS.  
CAUTION IS ALSO ADVISED FOR POTENTIALLY VERY STRONG WINDS AND  
VERY ROUGH SEAS IN AND NEAR ANY OF THE STRONGER THUNDERSTORMS  
THAT FORM NEAR THE COLD FRONT TONIGHT INTO TUE. FORECAST  
CONFIDENCE IS ABOVE AVERAGE OVER THE SHORT TERM.  
 
OVER THE MEDIUM RANGE WE WILL TREND THE FORECAST TOWARD THE  
VERY CONSISTENT 00Z ECMWF WINDS FOR TUE NIGHT THROUGH THU NIGHT  
OVER THE REGION, AND USE THE BOOST TOOL WHICH INCREASES THE  
ECMWF WINDS BY UP TO 15 PERCENT ON A SLIDING SCALE. WE WILL ALSO  
MAKE A FEW MANUAL EDITS IN DEFERENCE TO THE PREVIOUS FEW OPC  
FORECASTS, AND NEARBY COASTAL WFO AND TAFB GRIDS. THE NEXT  
THREAT FOR GALES WILL DEVELOP WED NIGHT THROUGH THU AS THE NEXT  
STRONG COLD FRONT CROSSES THE WATERS FROM NW TO SE. A LOW  
PRESSURE AREA MAY FORM ON THE STALLED FRONT, IN ADVANCE OF THE  
NEXT STRONG COLD FRONT, OFF THE N. CAROLINA COAST ON WED, WITH  
THE 00Z ECMWF STRONGER WITH THIS LOW AND ASSOCIATED WINDS VERSES  
THE GFS, UKMET AND CANADIAN GEM GUIDANCE. THEREFORE, WE WILL CAP  
WINDS AT 30 KT ASSOCIATED WITH THE LOW AS IT MOVES E OVER  
CENTRAL NT2 WATERS ON WED, AND CONTINUE TO CLOSELY MONITOR  
FUTURE MODEL GUIDANCE. OTHERWISE, WE EXPECT GALES TO DEVELOP AS  
THE SECOND STRONG COLD FRONT CROSSES THE WATERS WED NIGHT AND  
THU, WITH THE BEST CHANCE FOR GALES OVER EASTERN NT1 AND NE NT2  
WATERS. THERE IS SOME POTENTIAL FOR GALES OCCURRING FURTHER W  
OVER THE OFFSHORE WATERS WED NIGHT AND THU, AND WE WILL CONTINUE  
TO MAKE ADJUSTMENTS TO THE FORECAST OVER THE NEXT FEW DAYS.  
CONDITIONS WILL IMPROVE THU NIGHT INTO FRI AS HIGH PRESSURE  
BUILDS E OVER THE WATERS. THE HIGH WILL THEN SHIFT E OF THE  
WATERS FRI NIGHT AS YET ANOTHER COLD FRONT APPROACHES FROM THE W  
AND NW. FOR THU NIGHT THROUGH FRI NIGHT WE WILL RELY ON  
SOMETHING CLOSER TO THE 00Z ECMWF WINDS AND NOT BOOST THE WINDS  
OVER THIS TIME FRAME, AS FORECAST CONFIDENCE REMAINS NEAR  
AVERAGE, AND NO STRONG ADVECTION APPEARS LIKELY FOR MOST OF THIS  
TIME PERIOD. SOME ADJUSTMENTS WILL BE MADE IN DEFERENCE TO  
NEARBY COASTAL WFO AND TAFB WIND FORECASTS OVER THE MEDIUM  
RANGE. IT APPEARS THAT ANY GALES ASSOCIATED WITH THIS THIRD COLD  
FRONT WILL NOT OCCUR UNTIL SOMETIME OVER THE UPCOMING WEEKEND,  
AND THIS THREAT WILL BE ADDRESSED IN FUTURE OPC FORECASTS.  
 
SEAS...BOTH THE 00Z WAVEWATCH AND 00Z ECMWF WAM APPEAR TO HAVE  
INITIALIZED QUITE WELL OVER THE OFFSHORE WATERS EARLY THIS  
MORNING WITH SEAS HEIGHTS RANGING FROM 2 TO 5 FEET OVER THE  
REGION, WITH THE HIGHER SEAS OVER THE OUTER OFFSHORE WATERS.  
THESE TWO WAVE MODELS ARE IN PRETTY GOOD AGREEMENT OVER THE  
WATERS OVER THE NEXT 5 DAYS. WE WILL USE A 50/50 BLEND OF THESE  
TWO WAVE MODELS FOR THE EARLY MORNING PACKAGE, WITH A FEW MANUAL  
EDITS IN DEFERENCE TO NEARBY COASTAL WFO AND TAFB GRIDS, AND IN  
AND NEAR THE GALE FORCE WIND AREAS WHERE WE MAY ADD A FOOT OR  
TWO ESPECIALLY NEAR THE NORTH WALL OF THE GULF STREAM WHERE SEA  
HEIGHTS ARE TYPICALLY HIGHER IN STRONG COLD AIR ADVECTION IN THE  
WAKE OF STRONG COLD FRONTS.  
   
EXTRATROPICAL STORM SURGE GUIDANCE
 
THE LATEST ESTOFS AND ETSS  
GUIDANCE SHOW NO SIGNIFICANT POSITIVE SURGE OVER THE REGION FOR  
MOST OF THIS WEEK. NO MAJOR ADJUSTMENTS TO THE SURGE GUIDANCE  
APPEARS NECESSARY AT THIS TIME.  
 
   
WARNINGS
 
PRELIMINARY.  
   
NT1 NEW ENGLAND WATERS
 
   
ANZ800...GULF OF MAINE
 
 
GALE TONIGHT INTO TUESDAY.  
GALE POSSIBLE WEDNESDAY NIGHT INTO THURSDAY.    
ANZ805...GEORGES BANK WEST OF 68W
 
 
GALE TONIGHT.  
GALE POSSIBLE WEDNESDAY NIGHT INTO THURSDAY.    
ANZ900...GEORGES BANK EAST OF 68W
 
 
GALE TONIGHT INTO TUESDAY.  
GALE POSSIBLE WEDNESDAY NIGHT INTO THURSDAY.    
ANZ810...SOUTH OF NEW ENGLAND
 
 
GALE TONIGHT.   
ANZ815...SOUTH OF LONG ISLAND
 
 
GALE TONIGHT.  
   
NT2 MID-ATLANTIC WATERS
 
   
ANZ820...HUDSON CANYON TO BALTIMORE CANYON
 
 
GALE TONIGHT.   
ANZ915...HUDSON CANYON TO THE GREAT SOUTH CHANNEL
 
 
GALE TONIGHT.   
ANZ920...BALTIMORE CANYON TO THE GREAT SOUTH CHANNEL
 
 
GALE TONIGHT.  
GALE POSSIBLE WEDNESDAY NIGHT.   
ANZ905...THE GREAT SOUTH CHANNEL TO THE HAGUE LINE
 
 
GALE TONIGHT INTO TUESDAY.  
GALE POSSIBLE WEDNESDAY NIGHT INTO THURSDAY.    
ANZ910...EAST OF THE GREAT SOUTH CHANNEL AND SOUTH OF 39N
 
 
GALE TONIGHT INTO TUESDAY.  
GALE POSSIBLE WEDNESDAY NIGHT.  
 

 
 
.FORECASTER REINHART/MILLS. OCEAN PREDICTION CENTER.  
 
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