Marine Interpretation Message
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
AGNT40 KWNM 010055
MIMATN

MARINE WEATHER DISCUSSION FOR N ATLANTIC OCEAN
NWS OCEAN PREDICTION CENTER WASHINGTON DC
855 PM EDT TUE 30 SEP 2014

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

18Z GFS WAS VERY CONSISTENT WITH ITS PAST COUPLE PREVIOUS RUNS
BUT THERE REMAINS SIGNIFICANT SPREAD AMONG MODELS WITH PSN AND
TRACK OF SFC LOW CURRENTLY ABOUT 230 NM N OF BERMUDA AS IT
RETROGRADES W AND NW BACK TOWARD NERN NT2 WATERS/GEORGES BANK
WED NGT INTO FRI. MODEL DISCREPANCY IS ARTIFACT OF DIFFICULTY
WITH TIMING AND INTERACTION OF MULTIPLE UPPER SHRTWVS ROTATING
AROUND UPPER LOW CENTER NEXT FEW DAYS. AS EXPECTED THERE IS ALSO
LARGE SPREAD IN LATEST ENSEMBLE MEMBERS. PAST COUPLE RUNS OF
ECMWF ARE N OF GFS PSN WITH SFC LOW WHILE UKMET HAS CONSISTENTLY
BEEN DVLPG SFC LOW FURHTER W JUST N OF GULF STREAM WED. AS A
RESULT UKMET INDICATES STRONGEST N TO NE WINDS REACHING S OF
LONG ISLAND. WILL DISREGARD THIS WRN OUTLIER. 12Z GLOBAL GEM
MORE IN LINE WITH GFS AND 12Z ECMWF EPS MEMBERS ARE ALSO MORE
SUPPORTIVE OF GFS SOLUTION WHILE 12Z/18Z GEFS MEAN IS E OF
DETERMINISTIC GFS. WITH LOW FORECAST CONFIDENCE WILL MAINTAIN
PREVIOUS GALES OVER OUTER WATERS. GIVEN LATEST OBS AND 18Z
GUIDANCE WILL NOT BE MAKING MAJOR ADJUSTMENTS TO PREVIOUS WIND
GRIDS.

OVER WATERS S OF LONG ISLAND WHERE NE WINDS IN 15 TO 20 KT RANGE
LATEST BUOYS INDICATING THAT 18Z MULTIGRID WAVEWATCH III IS
ABOUT 1 FT TOO LOW THIS EVENING. WITH PREFERENCE FOR GFS BNDRY
LAYER OR 30M WINDS FOR THIS NE FLOW EVENT AND ALSO BASED ON
RECENT MWW3 PERFORMANCE WILL BUMP UP SIG WV HGTS OVER AREAS WITH
WINDS 25 KT OR GREATER BY 10 TO 15 PERCENT LATE TNGT THRU FRI.


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

THE 12Z SFC ANALYSIS INDICATED A WEAKENING STATIONARY FRONT OVER
THE NT1 WATERS...WITH WEAK LOW PRES OVER THE SRN NT2 WATERS AND
ANOTHER JUST NW OF BERMUDA. MORNING ASCAT PASS WITH DECENT
COVERAGE OVER THE OFFSHORE WATERS INDICATED WINDS MOSTLY 20 KT
OR LESS...WITH A SWATH OF 20 TO 25 KT WINDS INDICATED OVER THE
GULF OF MAINE. THE MODELS ALL INITIALIZED THESE WINDS TOO LOW
OVER THE GULF OF MAINE BY ABOUT 10 KT...AND ALSO EXPLAINS WHY
SEAS WERE ABOUT 2 TO 3 FT HIGHER THAN MWW3 MODEL.

THE MODELS ARE REASONABLY CLOSE THROUGH ABOUT 24 HOURS...THEN
DIFFERENCES BEGIN TO APPEAR AND CONTINUE THROUGH THE REMAINDER
OF THE PERIOD WITH THE MOST NOTICEABLE DIFFERENCES BEING THE
HANDLING OF LOW NW OF BURMUDA. THE 12Z GFS HAS TRENDED FURTHER W
AGAIN...SIMILAR TO THE 06Z RUN AND CONSIDERABLY FURTHER W THAN
THE 00Z GFS. THE CMC AND NAM ARE THE MOST SIMILAR TO THE 12Z
GFS...AND ALL ARE REASONABLY CLOSE WITH THE LOW POSITION AND
INTENSITY DURING THE 36 TO 84 HOUR PERIOD. LOOKING AT THE GFS
ENSEMBLE MEMBERS...A GOOD PORTION OF THE MEMBERS ARE EVEN
FURTHER W WITH THE LOW POSITION THAN THE OPERATIONAL RUN WHICH
STRENGTHENS THE CASE FOR INTRODUCING GALES INTO THE ERN PORTIONS
OF OFFSHORE WATERS THU INTO THU NIGHT. DURING THE EXTENDED
PERIOD...THE MODELS ARE ALL IN AGREEMENT MOVING COLD FRONT
OFFSHORE LATE FRI NIGHT INTO SAT. THE GFS CONTINUES TO BE
SLIGHTLY FASTER THAN THE OTHER MODELS. FOR THE SHORT TERM
PERIOD...PLAN ON POPULATING GRIDS USING THE 12Z GFS 30M
WINDS...THOUGH AS USUAL WILL MAKE FINAL DETERMINATION ON GRIDS
AFTER 12Z ECMWF IS AVBL. FOR THE EXTENDED PERIOD BEGINNING 12Z
SAT AND BEYOND...WILL USE THE ECMWF WINDS TO ACCOUNT FOR THE
SLOWER FRONTAL PASSAGE.

.SEAS...THE 15Z SEA STATE ANALYSIS INDICATED OBSERVED SEAS WERE
MOSTLY WITHIN A FT OF THE MWW3. SINCE WILL BE USING THE GFS WIND
GRIDS INITIALLY...WILL USE THE MWW3 VALUES THROUGH 12Z
SAT...THEN WILL TRANSITION TO THE ECMWF WAM FOR THE REMAINDER OF
THE PERIOD.
.EXTRATROPICAL STORM SURGE GUIDANCE...N/A.

.WARNINGS...PRELIMINARY.

.NT1 NEW ENGLAND WATERS...
.ANZ800...GULF OF MAINE...
     GALE POSSIBLE THU NIGHT.
.ANZ900...GEORGES BANK EAST OF 68W...
     GALE THU.
     GALE POSSIBLE THU NIGHT.

.NT2 MID ATLC WATERS...
.ANZ905...THE GREAT SOUTH CHANNEL TO THE HAGUE LINE...
     GALE POSSIBLE THU NIGHT.

$$

.FORECASTER CLARK/KOSIER. OCEAN PREDICTION CENTER.


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.