marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 934 am EDT sun Aug 2 2015
.Forecast discussion: major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.
Ltst NCEP sfc analys indc a stnry frnt acrs c and srn nt2...and a wk cdfnt acrs nt1. GOES vis imgry indc cnvctv wx alng the stnry frnt ovr the unstable envrmt in nt2...and the lgtng density prod indc sctrd showers and tstms...so planning on keeping mention in update pkg. However...convctv wx cont to have impacts on mdl solns...as 00z Gem...and to a lesser extend the 00z UKMET...cont to have lrg cnvctv feedback prblms with lows dvlpg alng frnt. Crnt sfc rprts and 02z ascat data indc wnds up to 25 kt alng the stnry frnt...and prev fcst indcd abt the same for 12z tda. The mdls agree fairly well in the short term with dvlpg anthr wk wave alng the stnry frnt and movg it off to the E. All but the Gem keep the wave wk...and the wkr solns were flwd in the prev fcst...so planning on staying the course in the update pkg.
Other than the 00z Gem/UKMET overdvlpg frntl lows thrut the pd...the mdls rmn in fairly gud agrmt thrut the pd. The 00z GFS/ecwmf had been in gud agrmt into Wed ngt...then diff with anthr low movg off the coast. However...the 06z GFS trended twd the 00z ecwmf soln...and is now in rsnbly gud agrmt on Thu and Thu ngt. The prev fcst favored the 00z ecwmf soln for Thu...and the 06z bolsters the sprt. As a result...not planning on mkg any sig changes for the rmndr of the update pkg.
----------------------------------------------------------------- Previous discussion...
Over the short term...the new 00z mdls present no major fcst problems. The most sig short term feature that the mdls fcst is a gradly strengthening sswly gradient dvlpg thrut most of the wtrs thru Mon nite btwn a gradly strengthening high pres ridge se of the ofshr wtrs and a inland cold front aprchg FM the NW. In this sswly gradient to varying degrees all of the mdls appear to be having sm convective feedback problems...with the 00z Gem/UKMET having the most problems as they both fcst svrl spurious sfc lows to track NE acrs the nt2 wtrs with gale (or in the Gem/S case storm) force ascd bl winds. Overall blv the rsnbly consistent 00z GFS solution...which also appears to hv sm mr minor feedback problems but is best sprtd by the 00z ECMWF...looks representative for this gradient. Therefore plan on populating our fcst wind grids with the 00z GFS 10m bl winds for today thru Mon nite...with sm additional edits in deference to the 00z ECMWF mainly to tweak down sm of its lkly too high winds in areas of convective feedback. So since the 12z GFS 10m bl winds were prevly used...anticipate making only minor short range chngs in the next ofshr fcst package.
In the long range...vs its prev respective runs...the 00z GFS rmns consistent in fcstg the cold front to mov ofshr Tue nite/Wed whl wkng...flwd by another scndry cold front pushing se acrs the nt1 wtrs late Wed/Wed nite...then bcmg stnry acrs the nrn nt2 wtrs Thu into Thu nite with a sfc low movg ofshr NE along the front Thu nite with 25-35 kt ascd 30m bl winds. The 00z UKMET gnrly sprts this GFS fropa timing but then fcsts a stronger frontal wave movg ofshr Thu nite. The 00z ECMWF also sprts the GFS fropa timing...but then late Thu/Thu nite fcsts multiple frontal waves movg ofshr with weaker ascd gradients. Based on the sheared upr lvl sprt and lack of sprt from the 00z gefs...wuld favor a weaker solution mr lk the 00z ECMWF on Thu/Thu nite... which also comes mr in line with the latest wpc medium range guidance then. Thererfore wl cont to populate with the 00z GFS 10m bl winds on Tue thru Wed nite...then wl transition to the 00z ECMWF bl winds on Thu/Thu nite. So as a result wl be making only minor chngs to prev ofshr fcsts on Tue thru Wed nite...but then sm mr sig chngs on Thu/Thu nite.
Seas...the 00z wavewatch iii and 00z ECMWF wam mdls hv both initialized the current seas well. Therefore with their ascd global mdls in rsnbl good agrmt...wl populate our fcst wave grids with a 50/50 blend of the two mdls for today thru Wed nite. The biggest impact of this blend wl be to tone down the 00z wavewatch iii fcst seas smwht mainly over the nt2 wtrs. Then since the 00z ECMWF wl bcm favored...wl transition to all 00z ECMWF wam fcst seas on Thu/Thu nite.
.Extratropical storm surge guidance...N/A.
.Nt1 New England waters... None.
.Nt2 mid Atlc waters... None.
.Forecaster Kells/vukits. Ocean prediction center.