Marine Weather for HS 100


marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 922 am EDT Thu may 28 2015

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

A weak cold front apchg the Appalachians is inducing return flow around the NW side of the subtrpcl rdg covering much of nt2 wtrs. With stable bl conds espcly over cooler shelf wtrs winds FM avbl sfc obs show SW winds up to 20 kt in glf of Maine and 15 kt or less elsw...with light winds in the ridge. The 00z/06z GFS 10m winds appr representative.

06z GFS is consistent with its previous run thru much of period but begins to diverge ovr the nrn wtrs begining late Mon as the New Run versus its previous two runs dvlps a closed sfc low in nrn nt2 wtrs Mon night which is not sprtd by other mdls or 00z/06z gefs ensemble members with GFS dvlpg a gale Tue. The only other mdl similar is 00z UKMET but it departs FM its previous run FM 27/12z. Will therefore cont to use previously populated 00z GFS 10m wnds thru fcst period with wnds capped at 25 kt and not repopulate with 06z GFS. 00z GFS is similar to 00z ECMWF and latest prelim wpc day 3-5 Med range guidance.

Seas...the 00z/06z wna ww3 and 00z ECMWF wam initialize too high by up to 2 ft over the cooler shelf waters over NW nt2 wtrs and much of nt1 waters...but otrw are close to 12z sea state analysis. With 00z GFS similar to its previous run thru Mon and preferred over 06z run Mon night will cont to use 00z wna ww3 excp trimmed seas in NW nt2 and ovr nt1 wtrs by 15 pct initially today into Fri mrng. ----------------------------------------------------------------- Previous discussion...

Ascat metop-a pass just after 00z returned S to swly 10-15 kt winds acrs the nrn half of the ofshr zns along the NW-ern periphery of a persistent watl ridge...while farther S of abt 36n mostly E to sely winds - also 10-15 kt range - were returned along the SW-ern extent of the ridge. The core stgst sfc winds are in the 20-25 kt range and still located in the Gulf of Maine...which matches well with both the ongoing fcst and the ltst 00z GFS 10m bl winds output. Max sig wvhts in this gradient are still running in the 6-8 ft range which is being handled well with the latest 00z wna ww3 attm.

Over the short term...the latest mdls remain in overall excellent agrmt that as the high pres ridge remains in place and a cold front aprchs FM the NW tda that the SW gradient acrs the nrn wtrs wl remain modly strong...if not weaken slightly. Then the mdls share smlr fcst timing for a wk cdfnt or sfc trof to slide ofshr into the nt1 wtrs tngt...then stall and dsipt Fri with wkng ascd fcst gradients that wl then persist into Fri nite. With the 00z GFS remaining consistent with each cycle and as compared to other global guid wl use the 00z GFS 10m bl winds thru Fri nite.

In the long range...perhaps the most sig feature thrut the fcst per wl be a cdfnt movg ofshr late Sat nite...pushing se acrs the nt1 wtrs sun...then stalling acrs the nrn nt2 wtrs sun nite into Mon nite whl strong high pres builds in N of the front. No surprises seen in the ltst 00z cycle of global guid this morn. The 00z GFS slowed fropa acrs the nt1 wtrs only abt 3 hrs compared to its 18z run...and rmns abt 3-6 hrs faster than the 00z ECMWF/Gem. The slightly faster / more progressive GFS has good support from 00z UKMET/navgem/gefs mean however...and conts to matches well with the ltst wpc Med range guid. For the morn grids wl cont using the 00z GFS 10m bl winds thru the end of the fcst per Mon nite. And it shud be noted that in the prev ofshr pkg we tamped down the postfrontal E-NE winds to the 20-25 kt range Mon/Mon nite...and wl cont to make these slight downward wind adjustments with the upcoming fcst pkg to get rid of specious 30 kt winds.

.Seas...Wl cont to use a 50/50 blended output between the 00z ww3 wna and 00z ECMWF wam thrut most of the fcst per. Will adjust values slightly downward twds the end of the fcst acrs nt1 and nrn nt2 - and limit Max sig wvht values to 8 ft - where winds were capped at 25 kt in the nely flow after fropa.

.Extratropical storm surge guidance...N/A.


.Nt1 New England waters... None.

.Nt2 mid Atlc waters... None.


.Forecaster Bancroft/Collins/vukits. Ocean prediction center.

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