HS 100

marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 915 PM 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.

As a warm front across the Gulf of Maine slowly drifts nwd the sswly gradient to its S has Max ascd winds gnrly up to 20 or 25 kt which are in line with the latest fcst mdls. Max ascd seas are in the 5-7 ft range which are also being handled well by the 18z wavewatch iii and 12z ECMWF wam attm.

Over the short term...the latest mdls remain in rsnbly good agrmt that the warm front wl push N of the nt1 wtrs overnite. Then a cold front is fcst to slowly aprch from the NW Thu...move ofshr Thu nite...then drift slowly E acrs the ofshr wtrs Fri into Sat while a frontal low tracks slowly NE acrs the nrn wtrs. Inadvof this cold front...per the 18z GFS and 12z ECMWF wl now adjust the prevly fcstd sly gales to start earlier (late Thu nite for the balt cnyn to the Hague line and ern balt cnyn to hat cnyn wtrs vs the prevly fcstd Fri into Sat. Also during this timeframe svrl of the mdls fcst prefrontal sly gale force bl winds to dvlp acrs the nrn wtrs...but for now blv the warm air advection over the cold wtrs N of the Gulf Stream wl keep strong enuf low level inversions in place to keep winds subgale there. So wl be making sm sig short term chngs in the next ofshr fcst package.

In the long range...plan on favoring the 18z GFS fcst timing for tracking the frontal low NE acrs the nt1 wtrs Sat/Sat nite...then slowly N of the wtrs sun into Mon. The 18z GFS timing looks like a rsnbl compromise btwn the faster 18z NAM/12z Gem/UKMET and slower 12z ECMWF and is also mr in line with the latest wpc medium range guidance. Late Fri/Fri nite the 18z GFS fcsts sm gale force bl winds dvlpg W of its fcst sfc low. But for now with the other global mdls fcstg weaker gradients wl keep the fcst winds W of the low subgale. So plan on making mainly minor long range chngs to the prev ofshr fcsts.

----------------------------------------------------------------- Previous discussion...

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 E across the srn nt1 wtrs Fri and Sat...track NE over the Georges Bank wtrs sun...then pass N of the nt1 area Mon. 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 and Mon.

Models...pattern wise and timing wise the 12z ECMWF/GFS are in gud agreemnt thru the fcst prd. The 12z Gem/UKMET are faster with the low over the Fri thru Mon timeframe...while the 12z NOGAPS is slower with the low...and 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 into Sat. 06z GFS overdoes strength of the W to NW flow bhd the cold fnt Sat into sun...so blending the GFS with the more conservative ECMWF here looks like a representative comprimise. Overall...will favor a blend of the 12z ECMWF/GFS thru the fcst prd.

Seas...since as noted abv am favoring a blend of the 12z ECMWF/GFS thru the fcst prd...will be using a blend of the 12z multigrid ww3 and ECMWF wam mdls.

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 Thu nite into Sat...mod confdc. .Baltimore Canyon to Hatteras Canyon...Gale Thu nite into Fri...low to mod confdc. .Hatteras Canyon to Cape Fear...None. .Cape Fear to 31n...None. $$

.Forecaster vukits/Scovil. Ocean prediction center.