marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 1009 PM EDT Thu Jul 2 2015
.Forecast discussion: major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.
00z NCEP sfc anal has a fntl bndry acrs the se nt1 wtrs to NE NC containing a fntl wave off VA CAPES. A weaker fntl bndry is stnry along outer nt2 wtrs and apprs marked by sct tstms. Ltg density prod shows convection most prevalent and heavier with first bndry ovr Carolinas and with both bndries invof glf strm. Are carrying wx in form of sct shwrs and tstms nrn and central nt2 wtrs and mainly shwrs srn nt1 where ltg density shows ltl actvty.
Latest mdls app well initialized and pick up on weak wave off Delmarva movg NE and offshore...sliding NE nr 1000 FM and a somewhat stronger fntl wave expected Sat also in mdls. Biggest threat for gales is with second wave on S side where 12z ECMWF/UKMET show some 30 kt 10m wnds during its passage but the usually more robust cndn is not that impressive and GFS peaks at 30 kt but for its higher 30m wnds which appr best representative alg/S of glf strm. With new GFS run showing ltlchg and with good overall mdl agrmt see no need to repopulate wnd grids.
Seas...the 18z wna ww3 and 12z ECMWF wam both indicate seas to 10 ft outer nt2 wtrs ascd with first wave with some differences dvlpg Sat with stronger fntl wave with differences mainly ovr nt2 wtrs. With 18z GFS showing ltlchg in sfc fcst the currently used mdl blend looks rsnbl. ----------------------------------------------------------------- Previous discussion...
The crnt GOES WV imgry indc an upr rdg nr 50w and an upr low ovr se Canada with a trof extending to S ovr the nt1 wtrs. The IR/vis imgry indc a frntl bndry acrs nt2...and the lgtng density prod shows cnvctn alng the bndry mainly ovr the Gulf strm. The ascat FM 1340z shows the less stable envmt ovr the glf strm...with wind rtrvls showing gales E of the ofshr wtrs in SW flow ovr it...and a marked dcrs in wnd intnsty to the N of it. The rscat pass rm 12z missed the highest areas of winds...but detected 30 kt alng the edges of the pass. Crnt sfc rprts indc wnd to 25 kt...but none are nr the highest winds indcd by ascat. The 12z GFS wnds are init OK when compared with the crnt data...but the 12z ECMWF/UKMET are init a ltl low. The 12z Gem and NAM are init OK ovr the glf strm...but the normal bias of too high wnds N of the glf strm appear in the initialization. With the GFS initialized abt the best...wl stay close to it in the short term.Also...wl maintain mention of tstms in the next pkg with lgtng density prod indcg them.
The 12z mdls agree fairly well thrut most of the fcst pd...and slowly wkn the upr rdg nr 50w into Mon...as sevl wk h5 vort maxes more ENE thru the W Atlc. At the sfc...the aforementioned sfc frnt wl stall ovr the W Atlc...as a cpl of wk lows mov E alng the bndry assoc with the wk srtwv energy that moves thru the area. The 12z mdls disagree slgtly on the tmg and track of the waves...but agree on the overall loc and intsty of the frnt. The 12z GFS has been a bit stgr with the wnds in the SW flow of the frnt than the ecwmf/UKMET...but wkr than the NAM/Gem...which show gales in SW flow...N of the glf strm...and seems overdone. Attm favoring the GFS solns...as it is a decent cmprms btwn the wkr and stgr solns. Planning on using the 30m wnds ovr the glf strm...which brings the wnds up to 30 kt on a few occasions. Wl also use the 10m wnds N of the glf strm...which seems rsnbl esp in light of the crnt scenario.
In the extended...the 12z mdls all indc the upr rdg wl wkn by Mon...as the trof swings thru the W Atlc. The 12z GFS/Gem indc a wave wl move along the prev frtnl bndry...and agree fairly well on the tmg and track. The 12z ECMWF/UKMET keep the low further W...and maintain the rdg ovr the ofshr wtrs. Attm uncertainty is high on the track...so planning on staying with the GFS...as it has been consistent.
.Seas...The 12z nww3 and ECMWF wam indc seas up to abt 10 ft ovr the ofshr wtrs...and agree somewhat well thrut a majority of the pd. Planning on using a 50/50 blend...as a cmprms to the minor diffs btwn the two solns.
.Extratropical storm surge guidance...N/A.
.Nt1 New England waters... None.
.Nt2 mid Atlc waters... None.
.Forecaster Bancroft/Kells. Ocean prediction center.