Marine Interpretation Message
Issued by NWS

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AGNT40 KWNM 280053
MIMATN

MARINE WEATHER DISCUSSION FOR N ATLANTIC OCEAN
NWS OCEAN PREDICTION CENTER WASHINGTON DC
853 PM EDT WED JUL 27 2016

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

NO CHANGES ARE PLANNED FOR THE EVENING UPDATE. SATELLITE IMAGERY
AND LIGHTNING DATA INDICATING MOST NEARLY ALL OF THE OFFSHORE
WATERS CONVECTION FREE WITH A FEW TSTSMS OVER THE N CAROLINA
COASTAL WATERS EXTENDING INTO FAR W OFFSHORE ZONES. THE 18Z GFS
WAS VERY SIMILAR TO THE PREVIOUS 12Z GFS THROUGH THE PERIOD. THE
00Z SEA STATE ANALYSIS INDICATED THAT OBSERVED SEAS MATCHED UP
WELL WITH THE MWW3/ECMWF WAM AND ALSO WILL NOT BE MAKING ANY
CHANGES TO WAVE GRIDS.

-----------------------------------------------------------------
PREVIOUS DISCUSSION...

ALTHOUGH THEY MISSED THE MAJORITY OF THE OUTER OFFSHORE WATERS
THE 1430Z AND 1530Z ASCAT OVERPASSES RETURNED HIGHEST WINDS OF
15 KT S OF CAPE HATTERAS. OVER THE NEAR TERM THE 12Z MODELS ARE
IN VERY GOOD AGREEMENT ACROSS THE W ATLC...WITH ONLY MINOR
POSITION DIFFERENCES WITH THE PERSISTENT QUASI STATIONARY FRONT
WHICH AT 18Z EXTENDED OFF THE MID ATLC COAST NEAR THE DELMARVA
PENINSULA WITH WINDS N OF HATTERAS 10 KT OR LESS THROUGH
TONIGHT. FRONT IS LIKELY TO DRIFT N THU WHILE SEVERAL WEAK LOWS
MAY DEVELOP ALONG THE NRN MID ATLC AND SRN NEW ENGLAND COASTS.
AS HAS BEEN THE CASE FOR THE LAST COUPLE DAYS GIVEN MODEL
AGREEMENT PLAN TO USE THE 12Z GFS WINDS THROUGH THU. BY THU
NIGHT AND INTO THE WEEKEND MODELS HAVE NOT SHOWN MUCH RUN TO RUN
CONSISTENCY AND ARE HAVING DIFFICULTY WITH THE TIMING OF A FEW
DEVELOPING (MOSTLY WEAK) SURFACE LOWS TO MOVE E ACROSS THE NRN
NT2 AND SRN NT1 WATERS ALONG THE FRONT. WITH THE STRONGEST LOW
LATE FRI INTO EARLY SAT THE 12Z UKMET HAS TRENDED TOWARD THE
MORE PROGRESSIVE GFS AND NAM SOLUTIONS. 12Z NAM IS A STRONG
OUTLIER THOUGH. THE 12Z ECMWF HAD A CONSISTENT TIMING WITH ITS
PREVIOUS RUNS BUT WAS STRONGER THAN ITS 00Z RUN.

WITH THE SLOWER ECMWF FAVORED...AS THE LOW PASSES NE THROUGH NT1
WATERS LATE FRI AND FRI NIGHT AND E OF THE AREA EARLY SAT...THE
ASSOCIATED COLD FRONT WILL PUSH SE THROUGH THE NRN AND CENTRAL
NT2 WATERS. MODELS ARE PRETTY CONSISTENT IN SHOWING 20 KT WINDS
S OF COLD AND EVENTUAL STATIONARY FRONT LATER SAT AND SUN. WITH
THESE 12Z MODEL TRENDS IN MIND AND TO KEEP SOME CONTINUITY WITH
PREVIOUS OPC FORECASTS PLAN TO BLEND 50 PERCENT OF THE 12Z ECMWF
WITH PREVIOUS OFFICIAL OPC GRIDS THU NIGHT THROUGH SUN. 12Z
MODELS THEN INDICATE THAT ANOTHER LOW WILL APPROACH THE LATE
SUN/ SUN NIGHT AND PASS E ALONG THE FRONT MON/MON NIGHT. GFS HAS
BEEN FLATTER THAN ECMWF/UKMET. WITH UKMET BETTER SUPPORTING
SLIGHLY STRONGER AND MORE NRN ECMWF PLAN TO FAVOR BLEND OF
00Z/12Z ECMWF SUN NIGHT THROUGH MON NIGHT WHICH WILL AGAIN
RESULT IN SOME 25 KT WINDS ACROSS NT2 WATERS S OF THE COLD FRONT
SUN NIGHT INTO MON NIGHT.

SEAS...THE 12Z WAVEWATCH III AND 12Z ECMWF WAM ARE REASONABLY
WELL INITIALIZED WITH WAVE HEIGHTS ACROSS THE W ATLC THIS
AFTERNOON WITH SEAS 4 FT OR LESS ACROSS BOTH NT1 AND NT2 WATERS.
THE ABOVE GUIDANCE IS IN VERY GOOD AGREEMENT OVER THE NEXT
COUPLE DAYS THEN BY LATE FRI AND THE WEEKEND THE WW3 AND ECMWF
WAM DIVERGE GIVEN THE TIMING DIFFERENCES WITH THE DEVELOPING
SURFACE LOW DISCUSSED ABOVE. TO BE CONSISTENT WITH WINDS WENT
WITH THE 12Z WW3 THROUGH THU...THEN BLEND OF 12Z ECMWF WAM WITH
PREVIOUS OPC GRIDS THU NIGHT THROUGH SUN...AND FINALLY BLEND OF
00Z AND 12Z ECMWF WAM FROM SUN NIGHT ONWARD.

.EXTRATROPICAL STORM SURGE GUIDANCE...N/A.


.WARNINGS...PRELIMINARY.

.NT1 NEW ENGLAND WATERS...
     NONE.

.NT2 MID ATLC WATERS...
     NONE.

$$

.FORECASTER KOSIER/CLARK. OCEAN PREDICTION CENTER.



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