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557
AGNT40 KWNM 291335
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
935 AM EDT Mon May 29 2017

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

1006 MB low pressure over Baltimore Canyon, near 38N 71W, is
moving east, per the preliminary 12Z OPC-NCEP surface analysis.
A ship located about 40 miles north of the low is reporting east
winds to 35 kt at 12Z this morning. After a QC check we see that
his bias is about 7 knots too high. We will continue to closely
monitor the latest observations and yet to arrive ASCAT overpass
to see if gales might be needed for a portion of the northern NT2
waters later today or tonight. For now, we will let the previous
grids and forecast ride, and more fully evaluate all of the 12Z
models once they arrive this afternoon. Some minor edits to fit
the ongoing forecast with current conditions and nearby TAFB and
WFO forecasts will be made for the morning update. The 06Z GFS
cycle is quite similar to the 00Z cycle which was used for the
early morning package.

As far as sea heights are concerned, we will make a few minor
edits and adjustments to the previous forecast to fit the grids
to current conditions and nearby WFO and TAFB grids and
forecasts. Otherwise, no major changes appear needed for the
morning update. Sea heights range from around 3 feet over the
northern Gulf of Maine and off the Georgia coast, to 8 feet
closer to the low as described above, off the northern mid-
Atlantic coast, per the 12Z RA1 OPC sea state analysis graphic.

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

Over the short term, the new 00Z models present no major forecast
problems. The models continue to forecast very similar tracks
for the surface low now near 38N73W to continue ENE across the
Nrn NT2 waters today, then pass SE of Georges Bank tonight. In
regards to the forecast gradients associated with this system,
believe the 00Z GFS solution looks resprentative. Per the 00Z
GFS, late today/early tonight it still looks close as to whether
the gradient immediately N of its forecast low will reach gale
force across the NE NT2 zone ANZ905. But with the GFS forecasting
low level stability to remain in place there, and the 00Z
UKMET/ECMWF forecasting slightly weaker gradients, will continue
to hold off on forecasting any gale warnings. So as was done
previously, will populate our forecast wind grids with the 00Z
GFS solution for this system by using our smart tool that will
place stronger 00Z GFS first sigma level winds in unstable areas
and weaker 00Z GFS 10m winds (which will be the predominant
winds) in stable areas for today through Tue night with some
minor additional edits mainly in deference to the 00Z ECMWF.

In the long range, the majority of the 00Z global models (the 00Z
global GEM looks like a too amplified and too strong solution
and hence will be disregarded) forecast a relatively quiet
weather pattern to persist. With generally minor timing
differences, the 00Z GFS/UKMET/ECMWF all forecast a warm front to
lift slowly NE from the central NT2 waters Tue night to across
the Nrn NT2 and NT1 waters by Wed/Wed night with weak associated
gradients (with max winds only in the 15-20 kt range). Then the
00Z GFS/UKMET/ECMWF share similar timing for a very weak (again
with at most only 15-20 kt associated winds) cold front to push
SE across the NT1 and Nrn/central NT2 waters Wed night/Thu, then
stall and dissipate Thu night. Therefore will continue to
populate with 00Z GFS first sigma/10m winds on Wed through Thu
night. Then late Fri/Fri night, versus its previous respective
runs, the 00Z GFS has trended slower with the next more
moderately strong cold front to approach the Nrn waters from the
NW, which is supported by the 00Z UKMET. The 00Z ECMWF though
remains consistent in forecasting a more progressive cold fropa.
So for now as a compromise, will continue to populate with 00Z
GFS first sigma/10m winds on Fri/Fri night, but in deference to
the 00Z ECMWF will then time shift these winds 6 hours faster.

.Seas...The 00Z Wavewatch III and 00Z ECMWF WAM have both
initialized the current seas reasonably well. With this in mind
and with their forecast differences remaining generally in the
1-2 ft range, will populate our forecast wave grids with a 50/50
blend of the two wave models (with the 00Z Wavewatch III time
shifted 6 hours faster Fri/Fri night) through Fri night.

.Extatropical Storm Surge Guidance...N/A.


.WARNINGS...Preliminary.

.NT1 New England Waters...
     None.

.NT2 Mid-Atlantic Waters...
     None.

$$

.Forecaster Mills/Vukits. Ocean Prediction Center.



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