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AGNT40 KWNM 261859

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
259 PM EDT Sun Mar 26 2017

.FORECAST DISCUSSION...Major features/winds/seas/significant
.weather for the North Atlantic Ocean W of 50W from 30N to 50N.

Over the short term, in association with the cold front across
the NT2 waters along 37N, an earlier 1522Z high resolution
ASCAT-B scatterometer pass confirmed that 20-25 kt winds were
present in the ENE gradient N of the front into the Srn NT1
waters. The new 12Z models are overall share similar forecast
timing that the front will stall by this evening, then lift
slowly back NEwd across the N waters as a warm front later
tonight into Mon night (with the max winds in the Ely gradient
immediately N and E of the front remaining generally in the 20-25
kt range), with a weak low racing E along the front across the
Gulf of Maine Mon night. Therefore as we have done for the past
several forecast packages, plan on populating our forecast wind
grids for tonight through Tue with the respresentative 12Z GFS
solution by using our smart tool that will place stronger GFS
first sigma level winds in unstable areas and weaker 12Z GFS 10m
winds in stable areas, with some minor additional edits in
deference to the 12Z UKMET/ECMWF.

Then, similar to the trend seen in its previous 06Z run, the 12Z
GFS by forecasting its associated Nrn stream upper trough to
amplify more slowly now forecasts an even more suppressed
surface solution with a weaker and more slowly intensifying
surface low tracking ENE near 40N Tue night/early Wed (which is
what the ECMWF had been forecasting all along) while pulling a
trailing cold front SE across the NT2 waters, then intensifying E
of the offshore waters later Wed into Thu night while supporting
a moderately strong Nly gradient back across the Ern NT1 and NE
NT2 waters. This 12Z GFS solution is now supported well by the
12Z UKMET/ECMWF/GEM/GEFS Mean. Therefore will continue to
populate with our GFS smart tool on Tue night through Thu night,
which will result in primarily stronger 12Z GFS first sigma level
winds being forecast in the Nly gradient. Will then make some
additional edits to these winds in deference to the 12Z ECMWF
with the biggest impact being to add possible NWly gales to NT2
zone ANZ905 on Thu/Thu night.

Then further out in the long range, since its supported by the
12Z GEFS Mean and in line with the latest WPC medium range
guidance, would favor a compromise between the similar 12Z
GFS/ECMWF solutions for a triple point surface low to move off
the Mid Atlantic coast Fri night while pulling a cold front
offshore. Therefore to develop this compromise, will populate
with a 50/50 blend of the 12Z GFS first sigma/10m and 12Z ECMWF
boundary layer winds on Fri/Fri night. So per this blend, will
forecast possible Sly prefrontal gales developing near the gulf
stream across the central NT2 waters Fri night.

.Seas...The 12Z Wavewatch III and 12Z ECMWF WAM have both
initialized the current seas equally well. With this in mind and
with their forecast differences remaining minimal, will populate
our forecast wave grids with a 50/50 blend of the two models for
tonight through Wed night. Then in the strong Nly gradient
Thu/Thu night, prefer the higher 12Z WAM, so will transition to a
66/33 blend of the WAM and Wavewatch III then. Then since a
compromise 12Z GFS/ECMWF solution will become favored, will
transition back to a 50/50 blend of the two wave models on
Fri/Fri night.

.Extratropical Storm Surge Guidance...N/A.


.NT1 New England Waters...

.NT2 Mid-Atlantic Waters...
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale Possible Friday night.
.ANZ905...The Great South Channel to the Hague Line...
     Gale Possible Thursday into Thursday night.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Gale Possible Friday night.


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