551  
AGNT40 KWNM 282354  
MIMATN  
 
MARINE WEATHER DISCUSSION FOR N ATLANTIC OCEAN  
NWS OCEAN PREDICTION CENTER WASHINGTON DC  
754 PM EDT SUN MAY 28 2017  
   
FORECAST DISCUSSION
 
MAJOR FEATURES/WINDS/SEAS/SIGNIFICANT  
.WEATHER FOR THE NORTH ATLANTIC OCEAN W OF 50W FROM 30N TO 50N.  
 
A LOW PRESSURE CENTER MOVING NE OFF THE VIRGINIA CAPES HAS MAX  
WINDS UP TO 20-25 KT IN ITS VICINITY. ASSOCIATED SEAS HAVE JUST  
BEGUN TO BUILD AND ARE ONLY IN THE 4-6 FT RANGE WHICH ARE BEING  
HANDLED SLIGHTLY BETTER BY THE 18Z WAVEWATCH III VERSUS THE 12Z  
ECMWF WAM AT THE MOMENT.  
 
OVER THE SHORT TERM, OVERALL THE LATEST MODELS SHARE VERY SIMILAR  
FORECAST TRACKS FOR THE SURFACE LOW TO CONTINUE ENE ACROSS THE  
NRN NT2 WATERS TONIGHT AND MON, THEN PASS E OF THE WATERS MON  
NIGHT. IN REGARDS TO THE FORECAST GRADIENTS ASSOCIATED WITH THIS  
SYSTEM, WOULD FAVOR A 18Z/12Z GFS AND 12Z ECMWF COMPROMISE. PER  
THE 18Z GFS, LATE MON/EARLY MON NIGHT IT LOOKS CLOSE AS TO  
WHETHER THE ASSOCIATED GRADIENT WILL REACH GALE FORCE ACROSS NT2  
ZONE ANZ905. BUT WITH THE MODEL FORECASTING LOW LEVEL STABILITY  
TO REMAIN IN PLACE THERE, THE PREVIOUSLY POPULATED 12Z GFS WINDS  
OF 25-30 KT STILL LOOK REPRESENTATIVE. SO WILL CONTINUE TO HOLD  
OFF ON FORECASTING ANY ASSOCIATED GALES WITH THIS SYSTEM AND WILL  
JUST MAKE SOME MINOR EDITS TO THE PREVIOUSLY POPULATED SHORT TERM  
WINDS AND SEAS.  
 
IN THE LONG RANGE, IN THE WAKE OF THE LOW PASSING E OF THE AREA,  
WOULD AGAIN FAVOR THE LESS PROGRESSIVE AND SIMILAR 18Z/12Z GFS  
AND 12Z ECMWF SOLUTIONS, VERSUS THE FASTER 12Z/18Z NAM  
AND 12Z GEM/UKMET, FOR A WEAK COLD FRONT TO APPROACH FROM THE W  
TUE, THEN PUSH SLOWLY OFFSHORE INTO THE NRN WATERS LATE TUE  
NIGHT INTO THU WITH WEAK (GENERALLY 15-20 KT). ASSOCIATED  
GRADIENTS. THEN THE 18Z GFS REMAINS CONSISTENT WITH ITS PREVIOUS  
12Z RUN IN FORECASTING A SLIGHTLY STRONGER COLD FRONT TO APPROACH  
FROM THE NW FRI, THEN PUSH OFFSHORE INTO THE NRN WATERS FRI  
NIGHT WITH MODERATELY STRONG (GENERALLY UP TO 20-25 KT)  
ASSOCIATED GRADIENTS. THE 18Z/12Z GFS FORECAST TIMING FOR THIS  
FROPA LOOKS LIKE A REASONABLE COMPROMISE BETWEEN THE SLIGHTLY  
MORE PROGRESSIVE 12Z ECMWF AND SLOWER 12Z UKMET/NAVGEM/GEM  
SOLUTIONS. SO WILL STAY THE COURSE WITH THE PREVIOUSLY POPULATED  
12Z GFS WINDS FOR THE LONG RANGE THROUGH FRI NIGHT.  
 
-----------------------------------------------------------------  
PREVIOUS DISCUSSION...  
 
LOW PRESSURE WILL MOVE EAST, AND THEN NORTHEAST ALONG A FRONT  
OVER CENTRAL AND THEN NORTHERN NT2 OFFSHORE WATERS TONIGHT INTO  
MONDAY. THE LOW IS LOCATED OVER NORTHEAST NORTH CAROLINA THIS  
AFTERNOON, WITH A NEARLY STATIONARY FRONT EXTENDING EAST FROM  
THE LOW OVER CENTRAL NT2 WATERS. ALL 12Z MODELS ARE NOW DEEPER  
WITH THIS LOW AS IT MOVES EAST AND NORTHEAST OVER THE REGION  
DURING THE NEXT DAY OR TWO. WE WILL REMAIN CLOSE TO THE 12Z GFS  
GUIDANCE OVER THE WATERS FOR THE NEXT FEW DAYS AS IT APPEARS TO  
BE IN VERY GOOD AGREEMENT WITH THE 12Z ECMWF, 12Z CANADIAN GEM,  
AND 12Z UKMET MODELS. IT ALSO HAS STRONG SUPPORT FROM THE 12Z  
NAM. WE WILL RELY ON THE SMART TOOL WHICH WILL PLACE THE  
STRONGER FIRST SIGMA LAYER WINDS OVER UNSTABLE AREAS, AND LOWER  
10 METER WINDS OVER STABLE AREAS THROUGHOUT THE FORECAST  
PACKAGE. AN AREA OF GALE FORCE WINDS IS NOW FORECAST TO DEVELOP  
JUST EAST OF THE NORTHEASTERN NT2 WATERS BY TUESDAY MORNING. WE  
WILL CLOSELY MONITOR THE LATEST MODEL GUIDANCE TO SEE IF ANY  
GALES MIGHT NEED TO BE ADDED TO THE OFFSHORE FORECAST. FOR THE  
AFTERNOON PACKAGE WE WILL KEEP MAXIMUM WINDS AT 30 KT FOR NOW,  
WITH CONFIDENCE LEVELS NEAR TO ABOVE AVERAGE.  
 
THE LATEST RADAR, SATELLITE AND LIGHTNING DENSITY DATA INDICATES  
SCATTERED THUNDERSTORMS OCCURRING NEAR THE FRONT, MOVING EAST  
AND NORTHEASTWARD TOWARD NORTHERN NT2 WATERS. THE STRONGER  
THUNDERSTORMS APPEAR TO BE DEVELOPING OVER NORTHEAST NORTH  
CAROLINA AND NEAR THE DELMARVA AT THIS TIME. THE LATEST SREF  
THUNDERSTORM GUIDANCE INDICATES THUNDERSTORMS SPREADING  
NORTHEAST FROM CENTRAL INTO NORTHERN NT2 WATERS INTO MONDAY,  
BEFORE MOVING EAST OF THE WATERS LATER MONDAY AS THE ASSOCIATED  
LOW ALSO PULLS EAST OF THE REGION. ADDITIONAL THUNDERSTORMS ARE  
POSSIBLE BY TUESDAY INTO WEDNESDAY AS A WEAK COLD FRONT AND  
POTENTIALLY ANOTHER LOW PRESSURE AREA CROSSES THE WATERS FROM  
WEST TO EAST. LOCAL WIND GUSTS EXCEEDING GALE FORCE AND VERY  
ROUGH SEAS MAY OCCUR IN OR NEAR ANY OF THE STRONGER  
THUNDERSTORMS.  
 
HIGH PRESSURE STILL APPEARS AS IF IT WILL BUILD BEHIND THE FRONT  
WEDNESDAY NIGHT INTO THURSDAY NIGHT. THE NEXT COLD FRONT WILL  
APPROACH FROM THE WEST FRIDAY, AND THEN POTENTIALLY BEGIN TO  
MOVE OFFSHORE FRIDAY NIGHT. THE 12Z GFS REMAINS THE FAVORED  
MODEL LATER IN THE WEEK, WITH THE 12Z ECMWF A LITTLE FASTER  
WITH THE FRONT, AND THE 12Z UKMET SLOWER. THE 12Z GEM IS FAIRLY  
CLOSE TO THE TIMING INDICATED BY THE 12Z GFS WHICH LEADS TO EVEN  
MORE CONFIDENCE IS USING THE 12Z GFS GUIDANCE FOR THE AFTERNOON  
FORECAST PACKAGE AND GRIDS.  
 
AS FAR AS SEAS ARE CONCERNED, IT APPEARS AS IF BOTH THE 12Z  
WAVEWATCH III AND 12Z ECMWF WAM HAVE INITIALIZED WELL OVER THE  
OFFSHORE WATERS BASED ON THE LATEST SEA STATE ANALYSIS AND  
ALTIMETER DATA. BOTH MODELS ARE FAIRLY SIMILAR THROUGHOUT THE  
FORECAST PERIOD, WITH THE WAM BUILDING SEAS A LITTLE FASTER  
LATER MONDAY AND MONDAY NIGHT AS LOW PRESSURE MOVES EAST OF THE  
WATERS. IT ALSO BUILDS SEAS A LITTLE FASTER BY FRIDAY NIGHT IN  
THE SOUTH AND SOUTHWEST FLOW AHEAD OF THE COLD FRONT DESCRIBED  
ABOVE. AS THE WAVEWATCH CAN TEND TO UNDER FORECAST SEAS IN THESE  
SITUATIONS WE WILL USE A 50/50 BLEND OF THE TWO WAVE MODELS FOR  
THE AFTERNOON PACKAGE.  
 
EXTATROPICAL STORM SURGE GUIDANCE: THE LATEST ETSS GUIDANCE STILL  
INDICATES A POSITIVE SURGE VALUE APPROACHING .3 TO .5 FOOT  
MONDAY INTO MONDAY NIGHT FROM CAPE MAY TO NEAR MONTAUK POINT.  
ESTOFS OUTPUT IS RUNNING A LITTLE HIGHER, CLOSER TO THE .5 TO 1  
FOOT RANGE. WE WILL PREFER SOMETHING A LITTLE CLOSER TO THE  
HIGHER ESTOFS MODEL OVER THE NEXT 24-48 HOURS AS MODEL GUIDANCE  
IS INDICATING A GOOD CHANCE FOR A SOMEWHAT STRONGER LOW AND  
THEREFORE STRONGER WINDS OCCURRING OVER THE OFFSHORE WATERS  
TONIGHT INTO MONDAY NIGHT, HELPING TO POTENTIALLY DRIVE A  
SOMEWHAT HIGHER SURGE FROM THE MID-ATLANTIC COAST NORTHWARD TO  
NEW ENGLAND.  
 
   
WARNINGS
 
PRELIMINARY.  
   
NT1 NEW ENGLAND WATERS
 
 
NONE.  
   
NT2 MID-ATLANTIC WATERS
 
 
NONE.  
 

 
 
.FORECASTER VUKITS/MILLS. OCEAN PREDICTION CENTER.  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page