marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 323 am EDT Tue Jul 28 2015
.Forecast discussion: major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.
The main fcst issue for the early am package will be the development and movement of low pres off the South Carolina coast Thu into the upcoming weekend. Except for this low pres area...little change will be made to the ongoing opc fcst with a stnry front persisting ovr srn nt2 wtrs thru Wed...with weak high pres N of the front ovr nrn nt2 off wtrs prevailing ovr these wtrs today into Wed before movg se toward Bermuda late Wed into Thu. Ovr nt1 off wtrs...a weak cold front is still fcst to move offshore tonite...stall ovr the wtrs Wed into Wed nite...and then return N as a warm front Thu. Another weak front will approach nt1 wtrs from the NW Thu nite into Fri...and move se into the nt1 wtrs Fri nite...followed by yet another weak cold front Sat nite. Low pres is now appearing more lkly to form off the South Carolina coast Thu. The low will intensify some as it tracks NE over central and then NE nt2 off wtrs Thu nite into Sat nite. There is some chance for gales dvlpg ovr portions of the ern and NE nt2 off wtrs later in the week into the wknd. For now...we do not feel confdc enuf to add them to the off wtrs fcst...so we will keep any gales that dvlp E of the off wtrs for the early am package...and cont to evaluate this possibility ovr the next few days.
Models...the 00z mdls are in decent agreement ovr the off wtrs today into early Thu. The 00z GFS has remained quite consistent from its past few mdl cycles so we will once again use the 10m GFS winds for the early am package for today into early Thu. By late Thu into the wknd...the 00z glbl mdl solutions begin to diverge. The 00z UKMET remains an outlier in bringing a dvlpg and rather intense looking tropical or sub-tropical system ovr the nt2 off wtrs Fri into the wknd...so it will cont to be ignored for this package. For the early am package for Thu and Thu nite we will use a 50-50 blend of the 00z GFS and 00z ECMWF mdls as they both indicate low pres forming off the South Carolina coast and tracking slowly NE. The 00z ECMWF is closer to the coast vs the 00z GFS...and we believe a blend of these two mdls seems like the best option for the fcst at this time. For Fri into Sat nite...we will transition to using just the 00z ECMWF mdl guid. We will...however...lower its winds by 10 percent ovr nt2 off wtrs for Fri into Sat nite...therefore keeping gales out of the off wtrs for this fcst package...as we would prefer to see a few more mdl cycles before adding gales to the off fcst.
Seas...both the 00z wna wave watch iii and 00z ECMWF wam WV mdls initialized well ovr the off wtrs per the latest obs and altimeter passes. For the short term portion of the fcst thru Wed nite we will remain close to the wna ww3 mdl output. For the long term part of the fcst...we will use a 50-50 blend of the 00z wna ww3 and 00z ECMWF wam mdls which will fit a little better with the wind fcst as noted abv. We will also lower sea hts fcst by a ft or two ovr mainly ern and NE nt2 off wtrs by Fri into the wknd as we lowered winds by 10 percent from the mdl guid ovr that region as described abv.
.Extratropical storm surge guidance...N/A.
.Nt1 New England waters... None.
.Nt2 mid Atlc waters... None.
.Forecaster Mills. Ocean prediction center.