Marine Weather for HS 100


marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 855 PM EST Wed Feb 21 2018

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

The latest NCEP surface analysis indicates a cold front along the New England coast this evening, and the 18z GFS indicates the front will move through the nt1 offshore waters tonight before stalling over the nrn nt2 waters on Thu. The 18z NAM and 12z Gem both agree well with the GFS on the timing, though the GFS is a bit stronger with the winds in the cold advection over nt1 once the front move S into Georges Bank. The GFS indicates up to 30 kt in the Gulf of Maine late tonight before high pres builds over the nrn zones Thu. However, the models maintain slightly higher winds just N of the front over nrn nt1/far SW nt1 in the NE flow between the front and the high to the N. The previous forecast had a brief period of 30 kt late Thu into Thu night. This still seems likely, so planning on staying near previous grids for the update package in the short range.

The available models (gfs, NAM, gem) all indicate another weaker cold front will move E across the area Fri night with winds up to 25 kt in SW flow ahead of the front. This supports the previous wind grids which went up to 25 kt, so not planning on making any major adjustments to them in the next forecast. The models then indicate a stronger low pres system will move through the area sun into Sun night, with a brief period of gales in the Gulf of Maine in the se flow ahead of the warm front. The GFS 925 mb winds indicates a strong level jet developing ahead of the warm front, with up to 50 kt at 925 mb. Despite the stable conditions over the colder waters in the Gulf of Maine, this should act to induce vertical mixing in the sheared environment. The previous forecast had gales in the Gulf of Maine and Georges Bank for sun into early Sun night. Confidence is about average with the gales as a result of the support from the rest of the available guidance, so planning on staying with the previous headlines. Otherwise, not planning on any major changes from the previous forecast.

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

Due to network problems at NWS/NCEP, recent available model data continues to be more limited than normal.

The 14z ascat overpass returned some limited areas of southwest winds to 25 kt south and southeast of Cape Cod and across the southern Gulf of Maine. These 25 kt winds have since expanded in areal coverage across the New England waters. The 12z GFS/NAM/ hiresw share a similar timing with the cold front which is will move off the New England coast this evening. Once front slows and stalls across the northern nt2 waters Thu, the winds south of the front should begin to diminish while the easterlies poleward of the front increase. The 12z GFS and 12z hiresw arw/nmm are slightly stronger than the 12z NAM with the easterly winds, and at this time we are favoring the stronger solutions. Will introduce winds to 30 kt late Thu into Thu night across the northern nt2 and southern nt1 zones. The latest available guidance then remained consistent in lifting the stationary front northeast as a warm front Fri and Fri night. Through 12z Fri we populated the wind grids with an even blend of the 12z GFS and 12z hiresw arw. Models then indicate a weak cold front will exit the New England and northern mid Atlantic coast Sat, which should again stall and weaken across the northern nt2 waters Sat night. Although the 00z/12z GFS did not dig the upper level shortwave trough as far southeast across New England as previous runs had, it remains the most amplified solution. The 12z GFS continued to show gale force winds developing across the nt1 waters northeast of the warm front sun into sun evening. With the wpc medium range winds even up to 33 kt, will be adding some marginal gales across Georges Bank and the Gulf of Maine sun. Toward the end of the forecast period the GFS/gefs are consistent in moving the next cold front offshore New England Sun night and across the nt2 waters Mon/Mon night. We will be populating the wind grids with the 12z GFS through the medium range.

.Seas: not surprisingly, given such a weak pattern, the 12z ww3 appears well initialized with the wave heights across the offshore and coastal waters this afternoon. The wave height grids are largely based on this guidance. We did adjust the wave heights about 15 percent or so higher across the northern nt2 waters in the strong east winds Thu and Thu night.

.Extratropical storm surge guidance: the 12z estofs is about twice as high (to 1.5 ft or so) as the 12z etss with the surge forecast to develop over Long Island Sound sun. These higher values my be underdone, based on the latest probabilistic etss whose mean values are about the same as the estofs output here.


.Nt1 New England waters... .anz800...Gulf of Maine... gale possible Sunday into Sunday night. .Anz805...Georges Bank west of 68w... gale possible Sunday. .Anz900...Georges Bank east of 68w... gale possible Sunday.

.Nt2 mid-Atlantic waters... None.


.Forecaster Kells/Clark. Ocean prediction center.

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