000
AGNT40 KWNM 260048
MIMATN

MARINE WEATHER DISCUSSION FOR N ATLANTIC OCEAN
NWS OCEAN PREDICTION CENTER WASHINGTON DC
848 PM EDT SAT APR 25 2015

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

A WEAK HIGH PRES RIDGE EXTENDING N TO S INVOF 70W IS MAINTAINING
LITE WINDS IN ITS VCNTY. IN RESPONSE TO LOW PRES DVLPG INLAND SSW
WINDS HV BEGUN TO INCRS OFF THE SE COAST AND ARE GNRLY IN THE
15-25 KT RANGE. MAX SEAS THRUT THE WTRS ARE IN THE 5-8 FT
RANGE...HIGHEST ACRS THE NE MOST NT2 WTRS...WHICH ARE BEING
HANDLED BETTER BY THE 18Z WAVEWATCH III THAN THE 12Z ECMWF WAM MDL
AT THE MOMENT.

OVER THE SHORT TERM...THE LATEST MDLS REMAIN IN RSNBLY GOOD AGRMT
THAT DVLPG LOW PRES WL RACE E ACRS THE NT2 WTRS NR 35N TONITE. PER
THE 18Z NAM/GFS WL BE ADDING MARGINAL ASCD SWLY GALES TO THE
OUTER S CNTRL NT2 WTRS (ZONES ANZ930 AND ANZ925) FOR TONITE. THEN
HV NO MAJOR PROBLEMS WITH THE 12Z/18Z GFS SOLUTIONS FOR ANOTHER
DVLPG SFC LOW TO FLW A SMLR TRACK SUN WITH SUBGALE ASCD WINDS.
THEN AS A COMPLEX CLOSED UPR LOW IS FCST TO DVLP E OF THE OFSHR
WTRS MON/MON NITE THE MDLS OFFER DIVERGENT SOLUTIONS FOR THE ASCD
SFC PATTERN. FOR NOW WULD FAVOR A BLENDED 12Z/18Z GFS AND 12Z
UKMET/ECMWF SOLUTION WHICH RESULTS IN A STRENGTHENING NLY GRADIENT
DVLPG THRUT MUCH OF THE OFSHR WTRS. THE PREVLY USED BLENDED 12Z
UKMET/ECMWF WITH THE WINDS THEN BOOSTED 20 PERCENT IS IN LINE WITH
THE 18Z GFS SO DO NOT PLAN ON MAKING ANY MAJOR SHORT TERM CHNGS TO
THE PREV OFSHR FCSTS.

IN THE LONG RANGE...ON TUE INTO WED THE 18Z GFS SOLUTION HAS COME
INTO BETTER AGRMT WITH THE 12Z ECMWF...WHICH ARE ALSO SPRTD BY THE
12Z GFS/UKMET...FOR THE STRONG NLY GRADIENT PERSISTING TUE/TUE
NITE...THEN WKNG WED. PER THE 18Z GFS IT LOOKS CLOSE AS TO WHETHER
THE SE MOST NT1 WTRS SHULD BE INCLUDED IN THE PREVLY FCSTD AREA OF
GALES ON TUE. FOR NOW WL NOT ADD GALES THERE BUT MAY RECONSIDER
LATER WHEN THE 00Z MDLS COME IN. SO PLAN ON MAKING ONLY MINOR
CHNGS TO THE PREV OFSHR FCSTS MON NITE INTO WED.

BY LATE WED INTO THU NITE...AS NOTED BELOW...THE DISPARITY BTWN
THE LATEST GLOBAL MDLS INCREASES SIGLY IN RGRDS TO A POTENTIAL
DVLPG SRN STREAM SFC LOW MOVG NE INTO THE SRN NT2 WTRS SO THAT NO
TWO MDLS OFFER A SMLR SOLUTION. SINCE IT BEST LINES UP WITH THE
LATEST WPC MEDIUM RANGE GUIDANCE...THE PREV FCST PACKAGE USED THE
12Z ECMWF SOLUTION FOR THIS SYSTEM BUT WITH ITS WINDS DECREASED ON
AVG BY 15 PERCENT. WITH ITS ASCD 12Z ECENS MEAN INDICATING THAT
THE 12Z ECMWF SOLUTION IS LIKELY TOO STRONG...A WEAKER SOLUTION
INDEED STIL LOOKS GOOD. SO WITH VERY LOW FCST CONFIDENCE WL NOT BE
CHANGING THE PREV NT2 FCST MUCH IN THE NEXT UPDATE.



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


IN SHORT...MODELS IN DECENT AGREEMENT THRU ONLY SUN TO SUN NGT THEN
GRADU FALL APART..ESP TOWARDS THE END OF THE FORECAST. LOW PRES
EXPECTED TO FORM ALNG DVLPG STNRY FRONT OFF THE NC COAST TNGT. THE
GFS/NAM DVLP THE LOW A LTTL FASTER AND MVS THE LOW OUT QUICKER...
BUT THIS SEEMS TO BE THE TREND. QSTN IS WHTHR SE WINDS WL REACH
GALE FRC OVR THE ERN HTTRS CNYN TO CAPE FEAR WATERS BEFORE 12Z.
LATEST GFS/UKMET/NAM 10M WINDS INCRS TO 30 KT...WITH GALES JUST E
DVLPNG JUST E OF THE OFFSHR WATERS. SECOND LOW WL FLLW SUN...
KEEPING MOD WESTERLIES S OF THE FRNT AS IT PUSHES S. MODELS IN
XCLLNT AGRMNT IN PUSHING FRNT S TO 31N ARND 06Z SUN NGT. ALSO..WL
NEE DTO HEAVILY EDIT WC GRIDS AS THE NAM AS THE AREA S OF CAPE
FEAR MOSTLY DRY TNGT AND SUN...DSPT INCRSNG CNVCTN HERE.

SUN NGT AND MON...SFC LOW IS EXPECTED TO STRNGHTN N OF BERMUDA...
WHILE SFC LOW S OF NOVA SCOTIA ALSO DEEPENS WHILE MVNG S TO SW.
ALOFT...MODELS ARE HVNG A DFFCLT TIME WITH UPR LOW FORMING S OF
NOVA SCOTIA AND THE ASSD ENERGY ROTATNIOG ARND THE LOW. THIS
CAUSES PRBLMS WITH THE SFC LOW OR LOWS ROTATING UNDR THE UPR LOW.
BY 12Z TUE...THE GFS FOCUSES MAINLY ON ONE STRNG SFC LOW ABT 500
NM SE OF NOVA SCOTIA WHERE THE UKMET/GEM/ECMWF MODELS PLACE A SFC
JUST SE OF GEORGES BANK. COMPARED TO THE GFS ENSMBL MEMBERS...THE
OP GFS RUN IS MUCH DEEPER WITH LOW NR 40N54W AT 12Z TUE AND SVRL
SUPPORT THE UKMET/ECMWF. THEREFORE...FROM 12Z MON ONWARD...WILL
DEPART FM GFS GDNC. FCST CNDFC CNFDC DCSRS IN TIME DUE TO THE
GLOBAL MODEL VRBLTY. BOTH UKMET/ECMWF FCST 10M WINDS INCRSNG TO TO
30 KT BY 12Z TUE. CNSDRNG GALES AR ALREADY IN PLACE AND FCST CNFDC
IS LOW...PLAN ON NUDGING UP THESE WINDS BY 10 TO 20 PCT TO KP
GALES IN THE FCST FOR CONTINUITY...USING A 50/50 UKMET/ECMWF
BLEND.

FOR TUE AND TUE NGT...UKMET/ECMWF TAKE SFC LOW S...THEN E AND
AGREE WELL.BOTH UKMET AND ECMWF INCRS NW WINDS TO 35 KT S OF
GEORGES BANK TUE...THEN AREA OF HIGHER WINDS WL MIGRATE EASTWARD
WITH ASSD SFC LOW TUE NGT.

WED...FOCUS OF EVENTS SHIFTS TO THE SRN WATERS WHERE EACH MODEL
BRINGS A SFC LOW E OFF THE GA COAST. THE UKMET IS ABOUT 6 TO 9 HRS
FASTER THE THE ECMWF. THE GEM HINTS AT THIS LOW...BUT IS VRY SLOW
AND WEAK BY COMPARISON. FOR WED NGT AND INTO THU...THE UKMET AND
ECMWF DIVERGE WITH THE UKMET TAKING A WEAKER LOW N OF BERMUDA AND
THE ECMWF TAKING LOW SLOWLY NE AND INTSNSYG IT AS THE ECMWF CUTS
OFF THE LOW ALOFT...AND DVLPS STORM FRC CONDS ON THE SFC. THE GFS
RMNS THE OUT MODEL OUT WITH A WK SFC RDF OFF THE SE COAST LATE WED
AND WK LOW IN THE GULF OF MAINE.

BY 00Z MAY 1...THE 4 GLOBAL MODELS HV 4 DFFRNT FCST. ANY BLEND WUD
WIPE OUT THE WIND CRCLTN. BOTH THE NEW UKMET AND ECMWF ARE
TRENDING FASTER AND WKR WITH THIS LOW. CNSDRNG THE ECMWF WAS USED
WITH THE 00Z OPC FCST...WL STAY WITH THE ECMWF BUT WL TRIM WINDS
BACK BY 10 TO 15 PCT.


.SEAS...THE 12Z MULTIGRID WAVEWATCH INITLD WELL AND LOOKS GOOD
WITH CURRENT CONDS. WAVE WATCH GDNC LKLS FINE...BUT WL TREND TWDS
THE ECMWF WAM SUN NGT AND MON...THEN GO WITH 100 PCT WAM GRIDS.
WILL TRIM BACK THE WAM SEAS BY 20 TO 30 PCT THU AND FRI AS THE
ECMWF WINDS WL BE TRIMMED BACK.


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



.WARNINGS...PRELIMINARY.

.NT1 NEW ENGLAND WATERS...
NONE.

.NT2 MID ATLC WATERS...
.ANZ915...HUDSON CANYON TO THE GREAT SOUTH CHANNEL...
GALE POSSIBLE TUE.
.ANZ920...BALTIMORE CANYON TO THE GREAT SOUTH CHANNEL...
GALE POSSIBLE MON NIGHT INTO TUE.
.ANZ905...THE GREAT SOUTH CHANNEL TO THE HAGUE LINE...
GALE POSSIBLE TUE INTO TUE NIGHT.
.ANZ910...EAST OF THE GREAT SOUTH CHANNEL AND SOUTH OF 39N...
GALE POSSIBLE TUE INTO TUE NIGHT.
.ANZ828...INNER WATERS FROM CAPE CHARLES LIGHT TO CURRITUCK BEACH LIGHT...
GALE POSSIBLE THU INTO THU NIGHT.
.ANZ925...OUTER WATERS FROM BALTIMORE CANYON TO HATTERAS CANYON...
GALE TONIGHT.
GALE POSSIBLE TUE.
GALE POSSIBLE THU INTO THU NIGHT.
.ANZ830...INNER WATERS FROM CURRITUCK BEACH LIGHT TO CAPE HATTERAS...
GALE POSSIBLE THU INTO THU NIGHT.
.ANZ833...INNER WATERS FROM CAPE HATTERAS TO CAPE FEAR...
GALE POSSIBLE THU INTO THU NIGHT.
.ANZ930...OUTER WATERS FROM HATTERAS CANYON TO CAPE FEAR...
GALE TONIGHT.
GALE POSSIBLE THU INTO THU NIGHT.
.ANZ835...INNER WATERS FROM CAPE FEAR TO 31N...
GALE POSSIBLE THU.
.ANZ935...OUTER WATERS FROM CAPE FEAR TO 31N...
GALE POSSIBLE THU INTO THU NIGHT.

$$

.FORECASTER VUKITS/PROSISE. OCEAN PREDICTION CENTER.