Marine Weather for HS 100


marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 841 PM EDT Fri may 22 2015

.Forecast discussion: major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.

As a cold front moves ofshr into the nt1 wtrs...Max ascd winds at the moment are gnrly in the 15-25 kt range. As the gale center now se of Nova Scotia conts off to the NE it has left seas gnrly in the 6-9 ft range acrs the NE nt2 wtrs which are being handled smlrly by the 18z wavewatch iii and 12z ECMWF wam mdls.

Over the short term...the latest mdls share smlr timing for the cold front to sweep se acrs the nt1 wtrs and into the nrn nt2 wtrs tonite...cont acrs the cntrl nt2 wtrs Sat...then dsipt acrs the srn nt2 wtrs Sat nite. In the wake of this stil looks marginal whether gales wl dvlp acrs the Gulf of Maine early Sat. But based on the consistent 18z NAM/GFS and the mod strong cold air advection fcstd...see no strong reasons to alter the prevly used 12z GFS 30m bl winds for this fropa. So as a result wl leave the prevly fcstd wrng in place. Then by late Sat/Sat nite the latest mdls are in good agrmt that a strong sfc high wl build in N of the front off the mid Atlc coast with dmnshg winds dvlpg thrut the wtrs. Again with the 18z GFS rmng consistent...wl cont to use the prevly populated weaker 12z GFS 10m winds by Sat nite. So as a result anticipate making only minor short term chngs to the prev ofshr fcsts.

In the long range...the latest mdls fcst a Summer type pattern to dvlp thrut the wtrs. In response to an upr ridge fcst to build nr the E coast Mon into Tue...then persist Tue nite into Wed nite the latest mdls are in gnrl agrmt that an ascd W-E sfc high pres ridge wl persist acrs the cntrl nt2 wtrs Mon into Wed nite whl gradly wkng. N of this ridge the mdls cont to differ smwht in their fcst strength of the swly gradient acrs the nrn wtrs. Blv the 12z/18z GFS and 12z UKMET/ECMWF offer a rsnbl compromise solution for this gradient vs the stronger 12z Gem and weaker 12z navgem. So plan on contg to use the prevly populated 12z GFS 10m bl winds with just sm minor additional edits in deference mainly to the 12z ECMWF.

----------------------------------------------------------------- Previous discussion...

Sfc low that was se of Nantucket this morning is now E of Georges Bank and accrltng NE at 45 kt. Scatterometer pass FM 15z missed the area of highest winds assd with this low. By this evening... xpect low to be near Sable Island and contg to move off to the NE. Following this low...cold front will quickly drop SSE across the waters tngt and weaken as it plunges S into the ridge. Models agree on the wrn prtn of the front mvg past balt cnyn by 12z... then dsiptg S of httrs cnyn Sat. Strngthng high pres will muscle in its way FM the W tngt...incrsng the NW gradient btn the high and scndry low ovr the gf of St lwrnc. GFS incrs NW winds to 35 kt ovr the gf of Maine by 12z...then eases winds back to W to SW 15 to 25 kt by 00z sun as the low quickly weakens. The GFS conts to fcst this brf period of gales early Sat and conts to be the model with the slgtly strngr winds. Since dffrncs are small and the models tend to underdo NW flow events...wl lv gales intact.

High pres will move off the mid Atlc coast Sat...then estblsh a W to E rdg alng 35/38n. The ridge will persist thru Tue night... then drift N and weaken Wed and Wed ngt as the upr rdg sloughs off to the E. Models agree on this ftr...with minor dffrncs noted in the details. Expect lgt E to NE winds S of httrs cnyn sun thru Wed ngt. A weak warm front may brush the wrn waters Mon...otw the the main challange wl be the timing and effect of weak sfc trofs gliding along the NW side of the rdg...producing SW winds of varying intnsty...15 to 30 kt ovr the nrn waters sun thru Wed ngt. Wl cont along with the current fcst with mainly lgt SW winds...except mod SW winds N of Cape Cod Mon ngt thru Wed ngt. The GFS rmns the strngst with these times about 5 to 10 kt higher then UKMET/ECMWF. Cnsdrng the incrsng ll inversion and stable flow...wl use the GFS 10m winds and ;limit them to 25 kt during this time.

.Seas...The 12z wavewatch iii has initialized well over the offshore waters...except it is about 2 ft underdone with the seas on the NW side of the gale se of Cape Cod. The wavewatch gdnc looks good...once the low quickly mvs off to the NE. The ECMWF wam gdnc looks a lttl too high with the sea in the SW wl stay wuith the wavewatch gdnc.

.Extratropical storm surge guidance...N?A.


.Nt1 New England waters... .anz800...Gulf of Maine... gale Sat.

.Nt2 mid Atlc waters... None.


.Forecaster vukits/prosise. Ocean prediction center.

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