Marine Interpretation Message
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
000
AGNT40 KWNM 300035
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
835 PM EDT Sat Apr 29 2017

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

Update...The 18z ncep surface analysis shows a cold front
approaching the new england and long island coasts from the nw,
with a large high pres ridge extending w over the nt2 waters, and
a robust pres gradient over the nrn and central nt2 waters
between the cold front and the ridge. Latest available ascat
hi-res and ascat passes from this morning show 20 to 25 kt winds
in sw flow over the nrn and central nt2 zones, with mainly 10 to
20 kt winds indicated elsewhere in the offshore waters.

Models...The medium range models are in good overall agreement
for tonight through Wed, so the representative gfs 10m/30m
solution with the stability smart tool will be used for the wind
grids for this timeframe. The models are showing timing
differences for the Wed night through Thu night timeframe, with
the ecmwf/ukmet models trending faster and the gem/gfs models
trending slower. Since the ecmwf was favored previously for wed
night through the rest of the forecast period, am planning to
stay with it until a model consensus emerges. So will use a
boosted version of the ecmwf for wed night through the rest of
the forecast period, in deference to the stronger gem/gfs
solutions. Confidence with the gale warnings for Mon night and
Tue is considered to be average to good.

Seas...The wna wavewatch and ecmwf wam both initialized well over
the coastal and offshore waters versus the latest observations.
The models are in good overall agreement for tonight through wed
with only minor differences noted, so a 50/50 blend of the wna
wavewatch and ecmwf wam will be used for the sea height grids
for this timeframe. Then will use the ecmwf wam exclusively for
wed night through the rest of the forecast period, in order to be
consistent with the ecmwf, which is the favored model solution
for that period.

Extratropical Storm Surge Guidance...N/A.

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

Over the short term, the new 12Z models overall remain consistent
and in reasonably good agreement. The models continue to share
similar forecast timing for a cold front to push SE across the
NT1 waters tonight, become quasi-stationary across the Nrn NT2
waters (near 38N) Sun, then return slowly NNE across the Nrn
waters as a warm front Sun night into Mon night with a gradually
strengthening associated Sly gradient developing throughout much
of the waters. Then with only slight timing differences, the 12Z
models forecast a cold front to move offshore late Sun night,
then continue slowly SE across the NT2 waters Mon into Mon night
while gradually weakening. Similar to its previous respective
runs, the 12Z GFS/NAM/GEM remain consistent in forecasting the
SSWly gradient in advance of the cold front to strengthen to gale
force Mon night into Tue across the NT2 waters primarily from
the gulf stream Swd. With the usually conservative 12Z
UKMET/ECMWF forecasting solid 25-30 kt boundary layer (BL) winds
in this gradient, continue to have above average forecast
confidence in these gales developing. Therefore plan on
populating our forecast wind grids with the respresentative 12Z
GFS solution for tonight through Tue 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, with minor timing differences, the 12Z models
all forecast a secondary cold front to sweep offshore Tue
night/Wed with the 12Z GFS remaining consistent in forecasting
the strongest associated gradients (up to 25 or 30 kt). For now
as a compromise will populate with a 50/50 blend of the 12Z GFS
first sigma/10m and 12Z ECMWF BL winds on Tue night into Wed
night. Then further out in the long range, the 12Z global models
continue to have timing differences in regards to the next
developing surface low forecast to move towards the mid Atlantic
coast Thu night. For now, with not a particularly high level of
forecast confidence, will favor the more progressive 12Z
UKMET/ECMWF solutions versus the slower 12Z GFS/GEM. Therefore
will populate with all 12Z ECMWF BL winds on late Wed night
through Thu night.

Seas...Other than being slightly too high across the NT1 waters,
the 12Z Wavewatch III and 12Z ECMWF WAM models have both
initialized the current seas elsewhere equally well. With this in
mind and since their associated 12Z GFS and 12Z ECMWF solutions
are similar, will populate our forecast wave grids with a 50/50
blend of the 12Z Wavewatch III and 12Z ECMWF WAM for tonight into
Wed night. Then since the 12Z ECMWF solution will become
favored, will transition to populating with all 12Z ECMWF WAM
seas late Wed night through Thu night.

.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 Possible Monday night into Tuesday.
.ANZ828...Inner Waters from Cape Charles Light to Currituck Beach Light...
     Gale Possible Monday night into Tuesday.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Gale Possible Monday night into Tuesday.
.ANZ830...Inner Waters from Currituck Beach Light to Cape Hatteras...
     Gale Possible Monday night into Tuesday.
.ANZ833...Inner Waters from Cape Hatteras to Cape Fear...
     Gale Possible Monday night into Tuesday.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale Possible Monday night into Tuesday.

$$

.Forecaster Scovil/Vukits. Ocean Prediction Center.



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.