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000
AGNT40 KWNM 161334
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
934 AM EDT Wed Aug 16 2017

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

GOES visible imagery is showing an eye appearing with Gert moving
to the NE which is just E or SE of the northern Mid Atlantic
offshore waters. Lightning activity was centered around the eye.
Seas associated with the system are estimated at 36 ft at 8 am with
further increases into the afternoon. The WWIII is much higher
than the ECMWF wam with the associated seas. ECMWF wam is about 6
ft lower than the WWIII. Hurricane Gert moves quickly off to the
NE this afternoon through tonight and Thu. Models are all in
good agreement with the track of Gert. Will await the NHC
official forecast with tropical storm force possibly extending W
into the eastern most areas of the northern mid atlantic
offshore East of 69W and south of 39N to 250 nm offshore and may
possibly into the zone East of 69W to the Hague Line between 1000
fm and 39N. Otherwise a cold front was moving into the New
England waters should move into the nrn Mid Atlantic waters
later tonight. A stationary front was just N of Gert at 8 am and
extended SW into the nrn Mid Atlantic offshore waters this
morning. With regards to updates will likely just adjust initial
conditions such as seas associated with Gert otherwise few
changes.

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PREVIOUS DISCUSSION...

The GOES infrared satellite imagery indicates Hurricane Gert just
E of the central NT2 offshore waters and moving to the NE. The
00Z GFS/ECMWF/UKMET/GEM models are all in good overall agreement
over the short range on the track, and indicate Gert will remain
strong while in close proximity to the Gulf Stream as it
continues to move NE today and tonight. As far as warnings are
concerned, the official guidance from NHC for Gert from the next
advisory will be used in the next offshore forecast, so will
update wind, wave, and hazard/warning grids once it is issued.
However, at first glance, it appears that the extent of tropical
storm winds could extend into the nrn NT2 zones, but the final
determination will be derived from the official forecast.

Otherwise, the 00Z models remain in good overall agreement
through the forecast period. In particular, the 00Z GFS and
ECMWF are in good agreement, and have remained so over the past
few runs. The models all indicate a weak stationary front will
develop across the central NT2 offshore waters in the wake of
Gert, and will into Thu night as a high pres ridge builds over
the nrn waters. The 00Z GFS then indicates the front will return
N through the area as a warm front Fri into Sat before a weak
cold front moves over the area Sat night and moved through the
area Sun. The 00Z ECMWF is slightly faster than the 00Z
GFS/UKMET, though all agree well on the intensity. For the next
forecast, am planning on using previous grids for today, and then
switch to the 00Z GFS 10m winds tonight and continue with it
for the remainder of the forecast as a result of the good
agreement.

Seas...Will start out with the previous wave height grids for
today, and will then switch to the 00Z Wavewatch tonight and
continue with it through the remainder of the forecast period as
it is supported reasonably well by the 00Z ECMWF WAM.

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


.WARNINGS...Preliminary.

.NT1 New England Waters...
     None.

.NT2 Mid-Atlantic Waters...
.ANZ910...East of the Great South Channel and south of 39N...
     Tropical Storm today.

$$

.Forecaster Rowland/Kells. Ocean Prediction Center.


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