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000
AGNT40 KWNM 301859
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
259 PM EDT Sun Apr 30 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, the new 12Z models overall remain consistent
and in very good agreement in regards to the expected synoptic
pattern. The models share similar forecast timing for a
stationary front now across the Nrn NT2 waters to return Nwd
across the waters as a warm front later tonight into Mon night
with a gradually strengthening Sly gradient developing throughout
the waters. Then late Mon night into Tue as a cold front is
forecast to push offshore the 12Z GFS remains very consistent
versus its previous respective runs in forecasting the Sly
gradient to strengthen to gale force across the NT2 waters S of
the gulf stream. With the 12Z GFS forecasting an associated 45-60
kt Sly low level 925 mb jet to develop over the NT2 waters in
association with this cold fropa and the usually conservative 12Z
UKMET/ECMWF now also forecasting gale force Sly prefrontal
boundary layer (BL) winds, forecast confidence is now high that
these gales will develop. Therefore as has been done for the past
several forecast packages, plan on populating our forecast wind
grids with the respresentative 12Z GFS solution for tonight
through Tue night using our smart tool that will place stronger
12Z GFS first sigma level winds in unstable areas and weaker 12Z
GFS 10m winds in stable areas (which will be over the majority of
the waters). So per these winds do not anticipate making any
significant timing and/or areal coverage changes to the
previously forecasted gale warnings on Mon night/Tue.

In the long range, by late Tue/Tue night the 12Z models agree
that the cold front will wash out and be followed by a secondary
cold front sweeping offshore Tue night/Wed, then stalling across
the S central NT2 waters Wed night with moderately strong
(generally up to 20-25 kt) associated gradients. So will continue
to populate with the representative 12Z GFS first sigma and 10m
winds on Wed/Wed night with some minor additional edits in
deference to the 12Z ECMWF.

Then further out in the long range, though they differ in regards
to their forecast tracks of the associated attendant surface low
tracking slowly NE from the SE conus Thu/Thu night towards New
York state by late Fri/Fri night, the 12Z global models in
general agree that the stalled front will slowly lift back Nwd
across the waters as a warm front Thu into Fri night, followed by
a cold front pushing offshore late Fri/Fri night. The primary
result of this pattern will be a strengthening Sly gradient
developing late Thu across the Srn NT2 waters and then spreading
Nwd Thu night into Fri night, with gale force winds likely
developing again across the NT2 waters primarily from the gulf
stream Swd. Overall will favor the 12Z GFS solution for these
fropas since its supported by the 12Z GEM/UKMET/GEFS Mean and is
only slightly less progressive than the 12Z ECMWF. Therefore will
continue to populate 12Z GFS first sigma and 10m winds on Thu
through Fri night.

Seas...The 12Z Wavewatch III and 12Z ECMWF WAM models have both
initialized the current seas throughout equally well. With this
in mind and since their associated 12Z GFS and 12Z ECMWF
solutions are similar and their forecast differences generally
remain in the 1-2 ft range, will populate our forecast wave grids
with a 50/50 blend of the 12Z Wavewatch III and 12Z ECMWF WAM
for tonight through Wed night. Then Thu and beyond since the 12Z
GFS solution will become preferred, will transition to populating
with all 12Z Wavewatch III seas then.

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

.WARNINGS...Preliminary.

.NT1 New England Waters...
     None.

.NT2 Mid-Atlantic Waters...
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale Monday night into Tuesday.
     Gale Possible Tuesday night.
     Gale Possible Friday night.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale Tuesday.
     Gale Possible Tuesday night.
     Gale Possible Friday night.
.ANZ828...Inner Waters from Cape Charles Light to Currituck Beach Light...
     Gale Monday night into Tuesday.
     Gale Possible Friday into Friday night.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Gale Monday night into Tuesday.
     Gale Possible Friday into Friday night.
.ANZ830...Inner Waters from Currituck Beach Light to Cape Hatteras...
     Gale Monday night into Tuesday.
     Gale Possible Friday into Friday night.
.ANZ833...Inner Waters from Cape Hatteras to Cape Fear...
     Gale Monday night into Tuesday.
     Gale Possible Friday into Friday night.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale Tuesday.
     Gale Possible Friday into Friday night.
.ANZ835...Inner Waters from Cape Fear to 31N...
     Gale Possible Thursday night into Friday.
.ANZ935...Outer Waters from Cape Fear to 31N...
     Gale Possible Friday night.

$$

.Forecaster Vukits. Ocean Prediction Center.


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