114
AGNT40 KWNM 202023
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
423 PM EDT Sun Aug 20 2017

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

Per the 18z OPC surface analysis a cold front was located across
the far northeastern NT2 waters, extending southwest across the
central NT2 waters to a point just off the North Carolina coast.
The latest ASCAT high resolution pass had data mostly over the
inner NT1 and NT2 waters where winds of 15 kt or less were
generally noted with the lightest winds in the waters off the
VA/NC coast and over ANZ835 in the southwest NT2 waters.

The 12z global guidance was in good agreement over much of the
NT1 and NT2 offshore waters into Wednesday with differences noted
heading into Thursday, more so over the NT2 waters in regards to
some guidance developing low pressure, possibly tropical in
nature, east of FL Tuesday/Tuesday night with it moving northeast
across the NT2 waters Thurs into Friday. Through Thursday high
pressure builds into the waters behind the departing cold front,
with the high moving east of the waters Tuesday as a second cold
front nears the region. Guidance is in good agreement concerning
frontal passage across the NT1 waters Wednesday into Thursday,
and over the NT2 waters Wednesday into Wednesday night.
Anticipate winds increasing over the NT1 waters and northern NT2
waters ahead of the cold front Tuesday but nothing to warning
level criteria.

As mentioned earlier guidance then begins to differ Thursday. The
12z UKMET/CMC develop low pressure east of FL in the Tuesday to
Wednesday time frame, strengthening the system as it moves
northeast across the southern and central NT2 waters
Thursday/Thursday night into in late Friday, then into the
northern NT2 waters Friday night. The 12z GFS/ECMWF also develop
a similar feature in the same area but are slower than the
UKMET/CMC solutions with development taking place east of FL
Friday night right at the end of the period or early Saturday,
just beyond the end of the period.

With all that noted will favor a 50/50 blend of the 12z GFS/ECMWF
through Thursday 00z. For the remainder of the period with the
differing solutions between the 12z GFS/ECMWF/UKMET/CMC feel its
reasonable to continue with a persistence forecast. This will
will consist of a 50/50 blend of the previous 00z GFS/ECMWF run
resulting in keeping the southern end of the second cold front over
the NT2 waters on days 4 and 5. Concerning the scenarios shown
in the UKMET/CMC and GFS/ECMWF camps later in or just beyond the
end of the forecast period in regards to low pressure or a
possible tropical system, will continue to monitor the situation
over the next several days and evaluate future model trends.


.SEAS...Favored a 50/50 blend of the 12z NWW3/ECMWF WAM through
Thursday 00z, transition to a persistence forecast beyond
resulting in a 50/50 blend of the prior 00z NWW3/ECMWF WAM model
runs.


.EXTRATROPICAL STORM SURGE GUIDANCE...n/a.


.WARNINGS...Preliminary.

.NT1 New England Waters...
None.

.NT2 Mid-Atlantic Waters...
None.

$$

.Forecaster Holley. Ocean Prediction Center.