North Atlantic Marine Weather Discussion

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AGNT40 KWNM 201406
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
1006 AM EDT Sat Oct 20 2018

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

The GOES visible satellite imagery shows low pressure over SE
Canada with a cold front extending to the SW into the Ohio Valley
region. Current surface reports over the offshore waters show
southerly winds ahead of the approaching front with winds up to
25 kt with a few reports up to 30 kt along the coast of Maine.
In addition, there have been reports up to gale force in the
outer NT2 waters, mainly in the unstable environment near the
Gulf Stream. The 06Z GFS and 00Z ECMWF both indicate winds will
continue to increase as low pressure develops along the front as
it moves into the region later today into tonight. The models
support the previous grids which have large areas of gale force
winds today into tonight and a small area of marginal storm
force winds in the outer northern NT2 waters for a brief period
tonight near the developing low. As a result of the model
support, confidence in the previous headlines with this frontal
system is above average, so planning on maintaining previous
headlines while making minimal edits to the grids.

The models continue to differ on the next system on Tue, and the
GFS has been consistently faster than the rest of the guidance as
it also keeps the associated surface low further N as it passes
to the N of the offshore waters. The rest of the 00Z guidance has
trended S with the track of the surface low, while the 00Z ECMWF
remained about 6 hours slower from the 00Z GEM/UKMET and 12 hours
slower than the GFS. The previous forecast continued to favor the
ECMWF solution, so a time shift was used to account for the
slower track of the ECMWF. Since this approach still seems
reasonable, am not planning on making any major changes to the
grids through the medium range period. This includes the warning
headlines on Tue night, so will continue with gales in several of
the northern zones with near average confidence.


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PREVIOUS DISCUSSION...

A cold front will move east across the waters and winds will 
increase ahead of the front with highest winds near the gulf 
stream in the short term. GOES 16 RGB Geocolor satellite images 
still show mostly clear skies over the waters but clouds are now 
entering the offshore waters and that is depicted well on the 
current NCEP weather map. The latest Scatterometer pass was about
0240Z and it showed weaker winds over the southern waters. In 
addition, the latest buoy and ship observations indicate 30 kt 
maximum winds. The latest NCEP weather map has high pressure east
of the central waters and it extends a weakening ridge across 
most of the region. Inland frontal boundary now approaching the 
mid Atlantic states will move across the waters in the next few 
forecast periods. 

At 500 MB, upper level ridge dominates the forecast waters with 
significant energy embedded in an upper level trough now over 
the mid west states. The models agree well in the short term on 
pushing the energy swiftly across the region. Models just differ
slightly on the timing of the energy as it moves east over the 
forecast waters. 

The latest run of models GFS/UKMETHR/ECMWFHR/CMC have 
initialized well the latest synoptic surface observations with 
just minor differences on the actual position of the front inland
that is moving east toward the waters and these differences 
increase in the short term. Models show enhanced winds near the 
gulf stream. GFS is rather fast and has storm force winds just 
east of the region while ECMWFHR though slower in moving the 
front than GFS, is weaker and does not show any storm force winds
near the waters. For consistency and farther collaboration, will
retain most of the official forecast winds and will stay with 
ECMWF in the extended period. 

.SEAS...They are initially less than 6 ft over the region are 
quickly building to over 6 ft with peaks around 12 ft by the 
issuance time. NWW3 and ECMWFWAVE have continued to initialize 
well the observed seas pattern and both wave models still agree 
well in the short term on swiftly building seas as the front 
passes over the waters. Unlike the winds, ECMWFWAVE will build 
the seas faster than NWW3 over the northern waters. Since we are 
still leaning toward ECMWF for winds, will also continue to use 
ECMWFWAVE for seas. 

.EXTRATROPICAL STORM SURGE GUIDANCE...There is no indication of
any significant positive surge events over the region for the 
next few days. 

.WARNINGS...Preliminary.

.NT1 New England Waters...
.ANZ900...Georges Bank east of 68W...
     Gale today into tonight. 

.NT2 Mid-Atlantic Waters...
.ANZ820...Hudson Canyon to Baltimore Canyon...
     Gale Sunday.
.ANZ915...Hudson Canyon to the Great South Channel...
     Gale today.
     Gale Sunday.
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale today into Sunday. 
.ANZ905...The Great South Channel to the Hague Line...
     Gale today.
     Storm tonight.
     Gale Sunday.
     Gale Possible Tuesday night.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale today.
     Storm tonight.
     Gale Possible Tuesday night.
.ANZ825...Inner Waters from Baltimore Canyon to Cape Charles Light...
     Gale Sunday.
.ANZ828...Inner Waters from Cape Charles Light to Currituck Beach Light...
     Gale Sunday.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Gale today into Sunday. 
.ANZ830...Inner Waters from Currituck Beach Light to Cape Hatteras...
     Gale today.
     Gale Sunday.
.ANZ833...Inner Waters from Cape Hatteras to Cape Fear...
     Gale today.
     Gale Sunday.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale today.
     Gale Sunday.

$$

.Forecaster Kells/Musonda. Ocean Prediction Center.