HS 100

marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 835 am EDT Wed 22 may 2013

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

Update:

Summary...a warm fnt will lift N across the nt1 wtrs this aftn and tonite. A cold fnt will move se toward the E CST Thu and Thu nite...then pass se and E over the ofshr wtrs Fri and Sat. Low pres will move NE alg the fnt Fri and Sat...then pass N of the nt1 wtrs sun. A hi pres rdg will persist over the nt2 wtrs into Thu mrng...then shift E of the ofshr wtrs later Thu into Thu nite. Another rdg will bld se into the nt2 area late Sat...then expand over the nt2 wtrs sun.

Models...pattern wise and timing wise the 06z GFS and 00z ECMWF are in vry gud agreemnt thru the fcst prd. The 00z Gem/UKMET are faster with the low over the Fri thru sun timeframe...while the 00z NOGAPS is slower with the low...so the ECMWF/GFS look like gud median solns wrt timing. 00z Gem is considered to be an outlyer soln because it signif overdoes the strength of the S to SW flow ahd of the cold fnt thru Fri. 06z GFS overdoes strength of the W to NW flow bhd the cold fnt Sat into sun...and blending the GFS with the more conservative ECMWF here looks like a representative comprimise. Overall...will favor a blend of the 06z GFS/00 ECMWF thru the fcst prd.

Seas...since as noted abv am favoring a blend of the 06z GFS/00z ECMWF thru the fcst prd...will be using a blend of the multigrid ww3 and ECMWF wam mdls.

Extratropical storm surge guidance...N/A.

Prev discussion:

Over the short term...the latest mdls present no major fcst problems. The 00z mdls and 12z ECMWF all fcst a front to remain qstnry acrs the nt1 wtrs today...then push N acrs the Gulf of Maine tonite as a warm front. A consensus of the 00z mdls for the fcst timing of this fropa looks fine. In regards to the gradly strengthening sswly gradient fcst to dvlp S of this front thru tonite wl compromise btwn the stronger 00z NAM/GFS and weaker 00z UKMET/12z ECMWF fcst gradients and wl cap the Max winds at 20 or 25 kt. Then on Thu into Thu nite as a cold front is fcst to aprch FM the NW and then slip ofshr late Thu nite...the latest mdls fcst the prefrontal sswly gradient to strengthen furthter. By late Thu/Thu nite wl use a compromise 00z GFS/UKMET and 12z ECMWF solution for this prefrontal gradient and wl cont to fcst Max winds up to 25 or 30 kt. So overall no sig short term chngs are planned for the next ofshr fcst package.

In the long range...on Fri into Sat as the cold front conts to slowly push ofshr...in response to strong upr level S/W trof fcst to dig into the NE conus to varying degrees that the latest mdls fcst a sfc low to dvlp on the front Fri and track NE acrs the nt1 wtrs Sat. For the timing of this frontal low wl compromise btwn the more progressive 00z Gem/UKMET/12z ECMWF and the slower 00z NAM/GFS. In regards to the fcst strength of this low and its ascd fropa gradients...believe the 00z Canadian global Gem solution is an outlier with storm force bl winds fcst nr its fcst frontal wave. Therefore overall wl again use a blended 00z GFS/UKMET and 12z ECMWF solution for the fcst strength of this system. So per this blended solultion...depending on what the 00z ECMWF comes in with later...wl now add the E portion of the balt cnyn to hat cnyn wtrs to the prevly fcstd prefrontal psbl gales on Fri.

Then by late Sat into sun...the 00z gefs indicates that the 00z GFS bcms too amplified with its fcst sfc low bcmg too strong and too slow to eject to the NE. Therefore for now wl not buy off on the nnwly gale force bl winds that the 00z GFS fcsts to dvlp Sat in the wake its sfc low acrs the nt1 wtrs. So with the 00z UKMET/Gem both fcstg weaker gradients than the 00z GFS...wl again wait to see the 00z ECMWF...but for now do not plan on making any sig chngs to the prev ofshr fcsts for the Sat/sun timeframe which were based on the 12z ECMWF and mr in line with the latest wpc medium range guidance.

The 00z wavewatch iii fcst seas look representative thrut the short term. But in the long range...especly by late Sat into sun...due to the stronger 00z GFS solution...believe the mdl is overfcstg the seas acrs the nrn wtrs and as a result wl lkly favor the ECMWF wam fcst seas then.

Extratropical storm surge guidance...N/A.

.Warnings/forecast confidence...Preliminary. Any changes will be coordinated through AWIPS 12 planet chat or by telephone:

.Nt1 New England waters... .Gulf of Maine...none. .Georges Bank...None. .South of New England...None.

.Nt2 mid Atlc waters... .Hudson Canyon to Baltimore Canyon...none. .Baltimore Canyon to Hague line...Gale Fri into Sat...low to mod confdc. .Baltimore Canyon to Hatteras Canyon...Gale Fri E portion...low confdc. .Hatteras Canyon to Cape Fear...None. .Cape Fear to 31n...None. $$

.Forecaster Scovil/vukits. Ocean prediction center.