marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 411 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.
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.
.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 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 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 prosise. Ocean prediction center.