Marine Interpretation Message
Issued by NWS

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AGNT40 KWNM 181940
MIMATN

MARINE WEATHER DISCUSSION FOR N ATLANTIC OCEAN
NWS OCEAN PREDICTION CENTER WASHINGTON DC
240 PM EST THU 18 DEC 2014

.FORECAST DISCUSSION: MAJOR FEATURES/WINDS/SEAS/SIGNIFICANT
.WEATHER FOR THE NORTH ATLANTIC OCEAN W OF 50W FROM 30N TO 50N.

1520Z HIGH RESOLUTION ASCAT-A RETURNED NW 30 KT OFF CAPE COD SW
TO NEAR WRN LONG ISLAND. AREA OF PRESUMED HIGHEST WINDS E OF 69W
WAS MISSED BY ASCAT. LATEST 13KM RAP AND HRRR IN AGREEMENT THAT
GALES SHOULD MOVE E OF OFFSHORE WATERS BY 21Z SO WILL GO AHEAD
AND ALLOW GLWS TO EXPIRE WITH NEXT ISSUANCES. 12Z MODELS ARE IN
GOOD AGREEMENT THAT NW WINDS WILL SLOWLY DIMINISH OVER NEXT 24
TO 36 HRS AS HIGH PRES BUILDS E TOWARD THE NEW ENGL AND MID ATLC
COASTS. FOR TONIGHT PERIOD WITH MODERATE COLD AIR ADVECTION
STILL OCCURRING WILL USE SLIGHTLY HIGHER 12Z GFS 30M WINDS THEN
WILL TRANSITION TO GFS 10M WINDS FRI. ALTHO 12Z MODELS HAVE COME
INTO SOMEWHAT BETTER AGREEMENT WITH SERIES OF WEAK UPPER SHRTWVS
EMBEDDED IN RELATIVELY ZONAL UPPER FLOW THIS WEEKEND INTO EARLY
NEXT WEEK. OVER LAST SEVERAL CYCLES MODELS HAVE ALMOST
UNANIMOUSLY TRENDED WEAKER AND SLOWER WITH DVLPG SFC LOW(S)
IMPACTING FAR WRN ATLC. THE EXCEPTION HAS BEEN THE PARALLEL GFS
WHICH AT 12Z STILL WAS ADVERTISING A COASTAL LOW NEAR LONG
ISLAND AND CAPE COD MON NIGHT AND EARLY TUE WITH STORM FORCE
WINDS. THE OP GFS TOO APPEARS TOO STRONG MAINLY IN DVLPG LEAD
LOW OFF SE COAST MON AND MON NIGHT. BOUNDARY LAYER WIND FIELD
EVEN SUGGESTS COULD BE SOME GRIDSCALE FEEDBACK ISSUE WITH THIS
DVLPMNT. ALTHO THE ECMWF HAS BEEN FAR FROM SHOWING ANY RUN TO
RUN CONSISTENCY AS WELL...ITS PAST COUPLE RUNS HAVE LOOKED MOST
REASONABLE ALBEIT 12Z RUN DOES LOOK SLIGHTLY TOO PROGRESSIVE.
OTHER THAN THIS TIMING ISSUE THO IT IS SUPPORTED BY 12Z UKMET AS
WELL AS LATEST GEFS AND ECMWF EPS MEANS IN MOVING WEAKER SFC LOW
ALONG COAST WHICH EVENTUALLY DISSIPATES OVER NEW ENGL LATE TUE
NIGHT AND EARLY WED. THERE IS SOME POTENTIAL THAT E WINDS COULD
REACH GALE OFFSHORE N OF ASSOCIATED WARM FRONT MON NIGHT INTO
TUE NRN MID ATLC AND NEW ENGL WATERS. HOWEVER GIVEN MODELS
PERFORMANCES OVER PAST FEW DAYS DO NOT HAVE SUFFICIENT FORECAST
CONFIDENCE TO ADD ANY GALES AT THIS TIME. BY LATE TUE/WED MODELS
ALL INDICATE SIGNIFICANTLY DEEP UPPER TROF MOVING INTO ERN US.
WILL AGAIN USE 12Z ECMWF WINDS BUT LIKE THE CASE SUN/MON WILL
SLOW DOWN BY ABOUT SIX HOURS. AND WILL NOT YET ADD ANY GALES TO
TUE NIGHT PERIOD. HAVE WELL ABOVE AVG FORECAST CONFIDENCE THAT
WILL SEE AT LEAST GALES AHEAD OF COLD FRONT WED WHICH IS JUST
BEYOND FORECAST PERIOD.

12Z MULTIGRID WAVEWATCH III CONTINUES ABOUT 1 TO 2 FT LOW WITH
SIG WV HGTS OVER OFFSHORE WATERS NEW ENGL WATERS AND NERN MID
ATLC WATERS. BUOY 44066 HAD 8 FT AT 19Z WHICH IS STILL A COUPLE
FT HIGHER THAN GUIDANCE. AFTER THESE INITIAL ADJUSTMENTS 12Z
MWW3 LOOKS OK THROUGH FRI. THEN WITH PREFERENCE FOR ECMWF
BEGINNING FRI NIGHT WILL USE ECMWF WAVE MDL FROM FRI NIGHT
ONWARD BUT WILL AGAIN ADJUST THIS GUIDANCE SLOWER BY SIX HOURS.

.EXTRATROPICAL STORM SURGE GUIDANCE...OVER PAST FEW RUNS ETSS
HAS HAD MUCH BETTER HANDLE THAN ESTOFS WITH NEGATIVE SURGE WHICH
IS ON ORDER OF -0.5 FT AT THE MOMENT. WATER LVL ANOMALIES
SUGGEST THAT ESTOFS -1 TO -1.5 FT ARE TOO NEGATIVE ABOUT -1 FT
DIFFERENT FROM ETSS WHICH HAS BEEN VERIFYING BETTER.

.WARNINGS...PRELIMINARY.

.NT1 NEW ENGLAND WATERS...
     NONE.

.NT2 MID ATLC WATERS...
     NONE.

$$

.FORECASTER CLARK. OCEAN PREDICTION CENTER.


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