Marine Weather for HS 100

Forecast

marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 847 PM EDT Sat Oct 25 2014

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

As a cold front aprchs FM the NW...the wswly gradient acrs the SW most nt1 and NW most nt2 wtrs has begun to strengthen with Max winds up to 20 to 25 kt pretty much as prevly expected. Elswhr lite winds prevail.

Over the short term...the latest mdls are in very good agrmt timing-wise for the cold front to mov ofshr tonite into nt1 and NW nt2 wtrs...then cont se acrs the rmng ofshr wtrs sun into sun nite while the attendant sfc low intensifies NE of the nt1 wtrs. The biggest fcst challenge remains how strong wl the wnwly gradient bcm behind the front. The prev fcst used the 12z GFS 30m bl winds for this gradient which resulted in marginal gale wrngs acrs the srn nt1 and nrn nt2 wtrs. With the 18z GFS rmng consistent and fcstg very smlr winds and the usually conservative 12z UKMET/ECMWF also fcstg solid 25-30 kt bl winds over these wtrs...do not plan on repopulating these 12z GFS 30m winds and wl just make sm minor edits in deference to the 12z UKMET/ECMWF. So do not plan on making any sig short term chngs to the prev ofshr fcsts.

In the long range...the latest global mdls gnrly agree that the only sig feature wl be a weaker cold front movg ofshr Wed into Thu...then bcmg stnry SW-NE acrs the nt2 wtrs Thu nite. To be mr in line with the latest wpc medium range guidance prefer the slightly slower 12z ECMWF/Gem/navgem fropa vs the faster 18z GFS/12z UKMET. So since the 12z ECMWF bl winds were used for this fropa anticipate making only minimal long range chngs in the next ofshr fcst package.

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

Summary...a weak ridge of high pres is crossing the off wtrs this aftn. The morning ascat pass indicated Max winds nr 25 kt occurring ovr the far NE nt2 off wtrs with winds gnrly 20 kt or less elsewhere. The ridge will pass E of the off wtrs this eve as a cold front approaches from the NW. Rather strong low pres assoc with the front will also move se and reach Maine early sun. The front will cross the wtrs tngt into sun ngt. A brief pd of gales is still fcst behind the front in the strong cold air adv ovr srn nt1 and nrn nt2 wtrs by sun ngt. Improving conditions are expected to dvlp Mon and Mon ngt as high pres slides E ovr the wtrs. The high will pass E of the region Tue as the next cold front approaches from the NW. This front will near the coast Tue ngt...and then move rather slowly se ovr the wtrs Wed into Wed ngt...lkly stalling ovr the se nt2 wtrs Thu into Thu ngt as wk high pres moves E off the New England and mid Atlc coasts.

Models...the 12z models are in vry good agreement ovr the off wtrs thru Tue ngt. We will therefore rely on the 12z GFS for the aftn package thru early Wed morning. We will use a blend of the 30m and 10m bl winds for the fcst N of the Gulf Stream...or roughtly N of 38n...for the period beginning tngt...and contg thru Mon ngt. This will produce a brief period of gales by sun ngt for zones 805... 810...915...and 905. These zones appear to have the best chance for more sustained gales per the latest nsharp GFS mdl soundings from that region. More widespread gale force gusts are lkly beyond this area from the new engl wtrs S to off the mid Atlc coast ltr tngt into Mon. For the aftn package we have decided to tone down the winds slightly from the 30m winds used prvsly as the remaining non-GFS bl winds are all sub-gale for ltr sun and sun ngt. Confdc lvls in these gales occurring is still moderate for the aftn package. Elsewhere the 10m bl winds from the GFS appear reasonable...and will be used for the fcst thru 12z Wed or 12z/29 Oct. Beyond that time mdl differences begin to increase. The 12z GFS becomes a slight outlier in movg the front faster than the remaining 12z glbl mdls for Wed into Thu. The 12z ECMWF appears to be a somewhat better fit with the majority of the guid which will keep the front movg slightly slower than the 12z GFS for ltr Wed into Thu ngt. As a result...from 15z Wed thru Thu ngt we will trend the next off fcst package toward the 12z ECMWF mdl guid.

.Seas...Sea hts range from nr 8 ft ovr wtrs well off the mid Atlc and NE coasts to 2 ft closer to the coastal wtrs from New England S to the Carolinas. For the most part the 12z wna WV watch iii mdl guid appears to have initialized well ovr the off wtrs per the latest obs. We will accept the wna ww3 mdl output for the next fcst package into early Wed...and then trend the fcst toward the ECMWF wam WV guid as we trend the wind fcst away from the GFS toward the 12z ECMWF at that time as well.

.Extratropical storm surge guidance...The latest essg appears reasonable ovr the region into next wk with no major surge events expected. The estofs guid and etss guid are fairly consistent thru early and middle parts of next wk. A modest neg surge will dvlp from the mid Atlc coast northward sun...and persist into Tue as a strong offshore wind field dvlps ovr the nt1 and nrn nt2 wtrs ltr tngt into Mon ngt.

.Warnings...Preliminary.

.Nt1 New England waters... .anz805...Georges Bank west of 68w... gale Sun night. .Anz810...South of New England... gale Sun night.

.Nt2 mid Atlc waters... .anz915...Hudson Canyon to the great South Channel... gale Sun night. .Anz905...The great South Channel to the Hague line... gale Sun night.

$$

.Forecaster vukits/Mills. Ocean prediction center.

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