000
AGNT40 KWNM 260811
MIMATN

Marine Weather Discussion for North Atlantic Ocean
NWS Ocean Prediction Center Washington DC
410 AM EDT WED 26 JUN 2019

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

Last evenings 0115z Ascat-B overpass indicated winds to 30 kt
associated with the thunderstorms which at that time were
located in the vicinity of 38N 71.5W. The 0140z ASCAT-A pass
returned multiple areas of south to southeast winds to 20 kt
near the warm front across the northern NT2 waters as well as
Georges Bank. Localized strong to gale force winds are likely
occurring with the new batch of convection near the Gulf Stream
across the outer ANZ920 and ANZ925 zones. GOES-16 imagery is
showing -65 to -72 Celsius overshooting cloud tops. Depending on
the trend seen in the lightning data, we may add specific
wording to note the higher winds expected in these thunderstorms
at least through ealry today. The high resolution guidance
including the HRRR does not seem to be well initialized with
these thunderstorms this morning. At 06z a 1012 mb surface low
was centered just south of western Long Island while a second
triple point low as located near Gloucester. The 00z models are
generally consistent that the southern low will becomen the
predominant feature as it tracks east northeast from south of
Long Island across Georges Bank today into Thu. The model
guidance, with the exception of the 00z GFS, mostly trended
stronger with the winds east of the low mainly over Georges Bank
today into tonight. Therefore, we have higher confidence with
the previously forecast 25 kt winds here. The low and cold
front should shift east of the offshore waters by early Thu,
with high pressure then expected to slowly move east over the
Mid-Atlantic waters Thu through into Sat. For the short term
wind grids through 00z/28 we used a blend of the 00Z ECMWF and
00Z WRF-ARW. Then through 21z/29 we transitioned to the 00z
ECMWF. However, given the relatively light winds forecast Thu
into early Sat, any of the models` wind fields appear
representative.

In the medium range, the 00z GFS and 00z ECMWF share a similar
timing with another low forecast to move east over New England
and approach the NT1 waters late Sat and Sat night along with a
cold front. The 00z GFS/ECMWF/UKMET all show west to southwest
winds increasing to 25 kt or so across the northern NT2 waters
Sat night. Then the 00z models diverge with a sharp upper level
trough or possibly a closed low expected to drop southeast
across the NT1 and northern NT2 waters late Sun and Sun night.
Generally the 00z global models, or at least the non-GFS
guidance, have backed off on the amplitude of the upper feature.
We cannot rule evenually developing gales with this system
especially over the northern outer NT2 zones near the Gulf
Stream Sun night. However, given the weakening trend seen in
some of the recent guidance, we will continue to keep winds
below gale force. The trend in the model guidane will be
monitored over the next couple days, with the chance for gale
force winds late in the weekend also being reevaluated. We used
a blend of the 00z GFS and 00z ECMWF for the wind grids Sat
night through the remainder of the forecast period.

.Seas: Both the 00Z Wavewatch and 00Z ECMWF WAM were 1 to 2 ft
too high across the NT1 waters at 00z, but elsewhere are well
initialized with the offshore wave heights this morning. The
aforementioned model guidance does not differ significantly with
the west Atlantic wave heights through the weekend. We used an
even blend of the 00z WW3 and 00z WAM for the wave height grids
through the period.

Extratropical Storm Surge Guidance: No significant positive
surge events are expected during the next several days. Consult
your National Weather Service office for more detailed and up to
date information.

.WARNINGS...Preliminary.

.NT1 New England Waters...
None.

.NT2 Mid-Atlantic Waters...
None.

$$

.Forecaster Clark. Ocean Prediction Center.