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AGNT40 KWNM 241932
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
232 PM EST Fri Feb 24 2017

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

GOES visible satellite imagery shows the exposed low level center
of a low pressure system just south of zone ANZ935 of the NT2
offshore waters, and a frontal boundary extending to the NE over
srn NT2. The imagery indicates an area of showers along the
front, though the lightning density product does not show much
in the way of convective activity despite the marginally unstable
environment. The 12Z models have backed off a little on the
instability, so tstms seem a little less likely. However, with
the boundary moving over the Gulf Stream, planning on maintaining
a mention of a chance of tstms. In addition, the Ascat wind
retrievals from late this morning indicated gale force winds
just east of the srn offshore waters, and up to 30 kt in
zone ANZ930. The GFS has shifted slightly east with the track of
the low, and indicates the strongest winds will stay just to the
east of the offshore waters tonight as the low starts
accelerating to the north in response to an upper trough moving
into the area tonight into Sat night. The 12Z ECMWF/UKMET/GEM
are all in decent agreement with the GFS on the track of the low
and on the intensity of the winds, and with keeping gales east of
the offshore waters with this low. As a result, will cap winds to
30 kt in the offshore waters with this low.

The 12Z models remain in good agreement in the short range, and
indicate a strong cold front associated with the aforementioned
upper trough will sweep through the offshore waters Sat into Sat
night. The 12Z GFS stayed consistent with previous runs, and
indicated periods of gale force winds in the strong cold
advection in the Gulf of Maine and in nrn NT2 over the Gulf
Stream Sat night into Sun night. The 12Z ECMWF/UKMET/GEM/NAM all
agree with the GFS on the strong cold advection, though the
ECMWF/UKMET are just below gale force despite having a similar
pressure gradient. The previous forecast had gales consistent
with the GFS which has been fairly consistent on this system, so
planning on keeping the gales with average confidence.

In the medium range, the models have trended toward the 12Z
GFS/ECMWF solution with a low moving off the New England coast
on Tue night. The ECMWF has trended a little stronger from
yesterday`s 12Z run, and now indicates the low will develop while
moving across the offshore waters. The 12Z GFS solution is a bit
stronger, and indicates gales will develop over the offshore
waters. Previous runs of the UKMET/GEM had not been indicating a
low, but the 12Z runs of both models have trended towards the
ECMWF/GFS solutions. In addition, more 12Z GEFS ensemble
members have trended toward a stronger low, so confidence is
increasing in the ECMWF/GFS solution. However, confidence with
gales is low as a result of the variability, so preferring to cap
winds at 30 kt in the next forecast on Tue. The GFS indicates yet
another low will move through the area on Wed. The 12Z ECMWF is a
little slower with this low, but the 12Z UKMET/GEM are more
progressive and are similar to the GFS. The models also indicate
strong development with this system, and the GFS shows another
round of gale force winds in the offshore waters on Wed. However,
confidence is low with the gales as a result of the high
uncertainty from the poor model agreement. Planning on using the
12Z GFS for the forecast, but will again cap winds at 30 kt.
Otherwise will stay with the 12Z GFS for the remainder of the
forecast period.

.As for the seas, the 12Z Wavewatch and ECMWF WAM are well
initialized in the vicinity of the offshore waters. The models
agree well into Mon night, so planning on using a 50/50 blend of
the two solutions. Will then use the 12Z Wavewatch exclusively
thereafter to reflect preferred weather model trends, but will
lower max seas several feet to account for capping winds at 30 kt
on Tue and Wed.

.EXTRATROPICAL STORM SURGE GUIDANCE...NA.

.WARNINGS...Preliminary.

.NT1 New England Waters...
.ANZ800...Gulf of Maine...
     Gale Sunday.
     Gale Possible Sunday night.

.NT2 Mid-Atlantic Waters...
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale Saturday night.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale Saturday night.
.ANZ828...Inner Waters from Cape Charles Light to Currituck Beach Light...
     Gale Saturday night.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Gale Saturday night.
.ANZ830...Inner Waters from Currituck Beach Light to Cape Hatteras...
     Gale Saturday night.
.ANZ833...Inner Waters from Cape Hatteras to Cape Fear...
     Gale Saturday night.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale Saturday night.

$$

.Forecaster Kells. Ocean Prediction Center.



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