Marine Interpretation Message
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000
AGNT40 KWNM 261446
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
1046 AM EDT Fri May 26 2017

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

The gale warnings in the NT2 zones will end by tonight and no
warnings are expected through the rest of the forecast period.
The satellite images show cyclonic circulation just west of the
NT1 waters with clouds with cold tops covering the north waters.
The lightning density map shows intense lightning northeast and
east of the region associated with a front that extends from the
circulation. Highest winds are in the gale force range over the
northern waters of NT2. At 1200Z the NCEP map has low pressure
996 mb over New England coast that has an occlusion stretching
northeast across the maine waters. High Pressure 1026 MB near
31N50W extends a weak ridge into the far southern waters. A
fairly tight pressure gradient over the north waters but mostly
relaxed elsewhere.

The seas are largest over the Baltimore canyon with a peak at 16
ft. Seas range between 9 and 15 ft over the north and central
waters while they range between 3 and 9 ft over the southern
waters with smallest seas over the southwest portion. The wave
models NWW3 and ECMWFWAVE have matched well the observed seas
pattern and both wave models have shown consistency in the
previous runs.

The models GFS/CMC/ECMWFHR/UKMETHR have initialized well the
1200Z surface observations with just minor differences on the
actual location of the low pressure center west of the north
waters. The models also have slight differences on the areal
coverage of the gale force winds. ECMWFHR and UKMETHR are weaker
than the observed winds while CMC is stronger than GFS and the
observed winds. There is a ship observation with 50 kt winds form
the northwest near 38N67W and no model is any closer to matching
the speed or direction and so will disregard the observation and
just keep winds in the gale force range. Will also continue GFS
mostly.

-----------------------------------------------------------------
PREVIOUS DISCUSSION...

Over the short term, the new 00Z models have converged towards
very similar forecast tracks for the surface low now near Long
Island expected to track NE across the Srn New England and the
Gulf of Maine today, then pass E of the NT1 waters tonight into
Sat. The models also share similar timing for an associated warm
front to lift N across the Gulf of Maine early today, while at
the same time the low pulls a cold front E across the remainder
of the NT1 waters. In regards to the forecast gradients the 00Z
GFS/ECMWF/UKMET/GEM share similar gradients supporting 25 to as
high as 30 kt north of the warm front in line with latest ASCAT
pass while given that the ECMWF initializes the low deeper than
other models and close to 06Z analyzed pressure will favor its
slightly higher boundary later winds in the W to SW flow south
of the low, retaining previously forecast gale warnings near the
Gulf Stream to start the new forecast. Therefore will populate
with the 00Z ECMWF through Fri night while boosting its 10m winds
along and south of the Gulf Stream.

For Sat. and beyond the 00Z ECMWF has suddenly offered a slower
solution for the warm front with waves expected to move over the
northern waters Sat night and beyond and will therefore prefer
the previous run or 12Z ECMWF for Sat night into Tue night
supported by 00Z GEFS and ECMWF ensemble means and 00Z UKMET.
Therefore will use the previous official grids for the remainder
of the forecast. The front will lift slowly Nwd Sun to Mon night
with several weak lows tracking E along the front. Then the
global models come into somewhat better agreement that a weak
cold front will approach from the NW Tue, then push offshore into
the Nrn waters Tue night. So since its been somewhat more
consistent, plan on favoring the 12Z ECMWF solution for this long
range pattern and as a result will populate with its BL winds
through Tue night.

.SEAS...The slightly higher 00Z Wavewatch III has intitialized
the current seas better than the 00Z ECMWF WAM. With this in mind
and since the ECMWF is otherwise favored, will populate our
forecast wave grids with 00Z Wavewatch III seas for today through
18Z then transition to 00Z ECMWF WAM this afternoon and tonight
and since 12Z ECMWF favored after Sat will transition to
populating with 12Z ECMWF WAM seas on Sat night through Tue
night.

.EXTRATROPICAL STORM SURGE GUIDANCE...The 00Z ESTOFS and
ETSS are 1 to 2 ft too low with the positive surge north of Cape
Cod with ESTOFS up to a half foot low along the mid-Atlantic
coast, while the ETSS has better handle initially with small
negative surges along SE coast, based on comparing with
observed water levels.


.WARNINGS...Preliminary.

.NT1 New England Waters...
     None.

.NT2 Mid-Atlantic Waters...
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale today.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale today.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Gale today.

$$

.Forecaster Musonda/Bancroft. Ocean Prediction Center.



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