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000
AGNT40 KWNM 071412
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
912 AM EST WED DEC 7 2016

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

At 12z NCEP surface preliminary analysis shows low pressure
continuing to move out to sea...near 37N 71W at analysis time.
Earlier ASCAT passes showed gales around the north and west sides
mainly south of 38N where the sea surfac temperatures are higher.
These conditions are close to the first sigma level winds off the
latest 06Z GFS. The morning update will have winds repopulated
with with similar winds off that model and verifying previous
forecast at 12Z. With the system continuing to track east and
weaken the new forecast will likely start with gales only over the
outer zone ANZ910. Maintained use of the GFS first sigma level
winds through Thursday night as Arctic high pressure slowly builds
into the area from the west containing a secondary cold front
moving offshore Thursday and Thursday night. For the remainder of
the period the previous forecast used grids from the old 06/00Z
ECMWF. Repopulated the grids with the new 07/00Z ECMWF which has a
slightly better handle on the cold surge following the cold
front...and with minor edits maintained previously forecast gale
warnings over the northern NT2 and the NT1 waters with the latest
models not digging the associated upper trough significantly...and
not supporting extension of northwest gales farther south.

Looking farther into the medium range the latest models diverge
Sunday and Sunday night on the timing of another cold front to
move toward the waters from the west. Favor the 00Z ECMWF 10m
winds...similar to the 00Z UKMET and WPC medium range guidance.

Seas...Repopulated the wave grids with the more representative 00Z
ECMWF WAM through Saturday night with a better handle on the
higher seas with cold advection. For the reason noted above on
Sunday and Sunday night continued to use the 00zECMWF WAM.
-----------------------------------------------------------------
PREVIOUS DISCUSSION...

Over the short term...A 0219Z high resolution ASCAT-B
scatterometer pass confirmed that gale force winds were present
throughout the nrn/central NT2 waters in association with the
strong surface low near 37N/73W. The new 00Z models are in
reasonably good agreement that the low will gradually weaken to
below gale force while tracking E across the central NT2 waters
today...then pass E of the waters tonight. Therefore based on the
impressive ASCAT pass and latest surface observations...would
though favor the slightly less progressive 00Z NAM/ECMWF solutions
which forecast a slower weakening gradient than forecast by the
quicker 00Z GFS/UKMET. So since the 00Z NAM/ECMWF are very similar
to the previous OPC official grids will not repopulate our
forecast winds for today into tonight.

Then Thursday into Thursday night the 00Z models share similar
forecast timing for an arctic cold front to push SE across the
waters. Similar to their previous respective runs...the consensus
of the new 00Z models is to now forecast a slightly weaker WNW
postfrontal gradient through Thursday night. So to depict this
weaker gradient will populate with the stronger 00Z GFS first
sigma layer winds for Thursday/Thursday night.

In the long range...As the 00Z models all forecast a strong high
pressure ridge to build in from the W...they forecast the WNW
gradient to strengthen...likely to gale force by late Friday into
Friday night but now over a more limited area. The 00Z global GEM
forecasts the strongest gradient with the most widespread area of
gale force associated boundary layer winds...while the 00Z
UKMET/ECMWF forecast weaker gradients. The 00Z GFS looks to
present a reasonable compromise solution for this gradient. So
will continue to populate with its stronger first sigma level
winds for Friday through Saturday night.

Then late in the long range...Sunday/Sunday night...Would
continue to favor the less progressive 00Z ECMWF solution for a
warm front to develop offshore with a strengthening sly
gradient...which are more in line with the latest WPC medium range
guidance...versus the faster 00Z GFS/GEM/UKMET solutions. Due to
problems at TOC...do not have the 00Z ECMWF winds available so for
now will continue to use the previously populated and similar 12Z
ECMWF boundary layer winds for Sunday/Sunday night.

.Seas...The 00Z Wavewatch III has initialized the seas across the
NT2 waters too low. Therefore will continue to use the previous
higher official wave grids for today/tonight. Then will populate
with the 00Z Wavewatch III for Thursday through Saturday
night...with these seas boosted up 10-15 percent late Friday into
Saturday night to better account for the strong cold air advection
in the NNW gradient. Then will transition back to the official
wave grids for Sunday/Sunday night.

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

.WARNINGS...Preliminary.

.NT1 New England Waters...
.ANZ800...Gulf of Maine...
     Gale Possible Friday into Friday night.
.ANZ805...Georges Bank west of 68W...
     Gale Possible Friday night.
.ANZ900...Georges Bank east of 68W...
     Gale Possible Friday night.
.ANZ810...South of New England...
     Gale Possible Friday into Friday night.
.ANZ815...South of Long Island...
     Gale Possible Friday into Friday night.

.NT2 Mid-Atlantic Waters...
.ANZ820...Hudson Canyon to Baltimore Canyon...
     Gale Possible Friday into Friday night.
.ANZ915...Hudson Canyon to the Great South Channel...
     Gale Possible Friday into Friday night.
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale Possible Friday night.
.ANZ905...The Great South Channel to the Hague Line...
     Gale Possible Friday into Friday night.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale today.
     Gale Possible Friday night.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Gale Possible Friday night.

$$

.Forecaster Bancroft/Vukits. Ocean Prediction Center.


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