034  
AGNT40 KWNM 150213  
MIMATN  
 
MARINE WEATHER DISCUSSION FOR N ATLANTIC OCEAN  
NWS OCEAN PREDICTION CENTER WASHINGTON DC  
1013 PM EDT TUE AUG 14 2018  
   
FORECAST DISCUSSION
 
MAJOR FEATURES/WINDS/SEAS/SIGNIFICANT  
.WEATHER FOR THE NORTH ATLANTIC OCEAN W OF 50W FROM 30N TO 50N.  
 
SCATTERED SHOWERS AND THUNDERSTORMS CONTINUE TO FIRE ACROSS THE W  
ATLANTIC AND OFFSHORE ZONES THIS EVENING, EVIDENCED IN GOES-EAST  
IR IMAGERY AND THE LIGHTNING STRIKE DENSITY PRODUCT. LOCAL GUSTS  
TO GALE FORCE ARE POSSIBLE IN OR NEAR ANY OF THE STRONGER  
CONVECTION. OTHERWISE, MOSTLY LIGHT WINDS GENERALLY 20 KT OR LESS  
PERSIST ACROSS THE WATERS IN SOUTHWESTERLY FLOW BETWEEN A WEAK  
STATIONARY FRONT DRAPED ALONG THE COAST, AND A HIGH PRESSURE  
CENTERED SOUTHEAST OF THE WATERS.  
 
THE ONGOING FORECAST AND GRIDS LOOK TO BE IN EXCELLENT SHAPE, AND  
CAN FIND NO OPPORTUNITIES TO IMPROVE UPON THE FORECAST ALREADY  
IN PLACE. WILL ONLY MAKE MINOR EDITS TO BEST MATCH NEIGHBORING  
COASTAL FORECAST OFFICE AND TAFB GRIDS, AND WILL RE-EVALUATE  
ENTIRE FORECAST WITH UPCOMING 00Z SUITE OF GUIDANCE LATER IN THE  
SHIFT.  
 
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PREVIOUS DISCUSSION...  
 
THE 1410Z AND 1450Z ASCAT OVERPASSES RETURNED WINDS UP TO 20 KT  
OUTSIDE OF THUNDERSTORMS. HOWEVER WITHIN AND NEAR THE  
THUNDERSTORMS ACROSS THE OUTER ANZ930, ANZ920, AND ANZ910 ZONES,  
WINDS TO AT LEAST 30 KT WERE OBSERVED. NUMEROUS OUTFLOW  
BOUNDARIES WERE AGAIN SEEN IN THE LATEST GOES-16 VISIBLE  
SATELLITE IMAGERY MAINLY ACROSS THE NT2 WATERS SOUTH OF  
BALTIMORE CANYON OVER THE LAST COUPLE HOURS, WITH STRONG TO GALE  
FORCE WINDS LIKELY ASSOCIATED WITH THESE BOUNDARIES. WE WILL  
LIKELY CONTINUE TO INCLUDE THE MENTION OF GALE FORCE WINDS IN  
THUNDERSTORMS THROUGH THE FIRST PERIOD ACROSS SEVERAL NT2 ZONES.  
COMPARED TO THIS MORNINGS ASCAT DATA, THE 14Z HRRR WAS  
REASONABLY WELL INITIALIZED, AND THE 18Z HRRR APPEARS TO HAVE A  
REASONABLE HANDLE ON THE STRONGER WINDS NEAR THE THUNDERSTORMS.  
THROUGH THIS EVENING, WE USED A BLEND OF THE 18Z HRRR AND 12Z  
NAMNEST FOR THE WIND GRIDS. AT 18Z THE UPPER LEVEL LOW WAS STILL  
INLAND, WILL APPROACH THE NEW ENGLAND COAST TONIGHT, AND WILL  
MOVE SLOWLY EAST ACROSS THE NT1 WATERS WED. AS THE UPPER FLOW  
BECOMES MORE WEST AND NORTHWEST LATE WED NIGHT AND THU, THE  
THUNDERSTORMS SHOULD BECOME MORE LIMITED ACROSS THE OFFSHORE  
WATERS. THE 12Z MODELS ARE GENERALLY IN GOOD AGREEMENT ACROSS THE  
WEST ATLANTIC FOR THE NEXT SEVERAL DAYS. THE WARM FRONT ACROSS  
THE NEW ENGLAND WATERS WILL LIFT NORTH OVER THE REST OF THE  
WATERS TONIGHT AS LOW PRESSURE DRIFTS NORTH AND NORTHEAST FROM  
NEAR NYC. THE COLD FRONT ALONG THE MID ATLANTIC COAST WILL DRIFT  
EAST TONIGHT AND DISSIPATE WED.  
 
BY LATE WED NIGHT AND THU, A LOW PRESSURE TROUGH AND SECONDARY  
WEAK COLD FRONT TO PUSH E AND SE OVER NT1 WATERS WED NIGHT AS  
LOW PRESSURE MOVES NE OVER THE CANADIAN MARITIMES, AND HIGH  
PRESSURE BUILDS JUST SE OF THE OFFSHORE WATERS. THE FRONT WILL  
LIKELY STALL AND REMAIN WEAK OVER SOUTHERN NT1 OR POSSIBLY  
NORTHERN NT2 WATERS THU AS HIGH PRESSURE DOMINATES THE SOUTHERN  
PORTION OF THE NT2 WATERS. THE 12Z GFS AND 12Z ECMWF THEN ARE  
CONSISTENT IN MOVING A LOW ALONG THE NEW ENGLAND COAST FRI NIGHT  
WITH AN ASSOCIATED SOMEWHAT STRONGER COLD FRONT THROUGH THE NT1  
AND NORTHERN NT2 WATERS SAT AND SAT NIGHT. THE AFOREMENTIONED  
MODELS ARE ALSO IN EXCELLENT AGREEMENT THAT THAT LOW PRESSURE  
WILL FORM ALONG THE STALLED FRONT NEAR THE VIRGINIA TIDEWATER  
AREA LATE SUN. MAINLY TO KEEP MORE CONTINUITY WITH THE PREVIOUS  
FORECAST WE ARE FAVORING THE 12Z ECMWF THROUGH THE MEDIUM RANGE,  
WHICH IS ALSO SUPPORTED BY THE LATEST WPC MEDIUM RANGE GUIDANCE.  
ONCE AGAIN THROUGH THE FORECAST PERIOD WINDS ARE NOT EXPECTED TO  
REACH ANY WARNING CRITERIA, OUTSIDE OF THE THUNDERSTORM ACTIVITY  
THROUGH WED NIGHT, WITH CONFIDENCE IN THE FORECAST REMAINING  
ABOVE AVERAGE.  
 
SEAS...THE 12Z WAVEWATCH AND 12Z ECMWF WAM ARE IN EXCELLENT  
AGREEMENT WITH THE OFFSHORE WAVE HEIGHTS THROUGH THE END OF THE  
WEEK. THE WAVE HEIGHT GRIDS WERE POPULATED WITH THE 12Z  
WAVEWATCH THROUGH THU, THEN TO BE CONSISTENT WITH THE FAVORED  
WINDS WE USED THE 12Z ECMWF WAM BEGINNING THU NIGHT.  
   
EXTRATROPICAL STORM SURGE GUIDANCE
 
NO SIGNIFICANT STORM SURGE  
IS EXPECTED THROUGH THE REMAINDER OF THE WEEK. LATE IN THE  
WEEKEND AS BOTH THE GFS AND ECMWF INDICATE MODERATE EAST TO  
NORTHEAST WINDS DEVELOPING NORTH OF THE COLD FRONT OFF THE MID  
ATLANTIC COAST, THERE COULD BE SOME MINOR SURGE THAT DEVELOPS  
FROM NEW JERSEY TO THE DELMARVA PENINSULA.  
 
   
WARNINGS
 
PRELIMINARY.  
   
NT1 NEW ENGLAND WATERS
 
 
NONE.  
   
NT2 MID-ATLANTIC WATERS
 
 
NONE.  
 

 
 
.FORECASTER COLLINS/CLARK. OCEAN PREDICTION CENTER.  
 
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