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North Atlantic Marine Weather Discussion

AGNT40 KWNM 220222
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
1022 PM EDT Thu Mar 21 2019

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

Low pressure over the mid Atlantic states will continue to move 
northeast as pressure gradient tightens over most of the the 
northern and central waters and that will be followed by high 
pressure that will build in from the southwest in the short term.
High pressure will then move east across the waters and pressure
gradient will be relaxed in the extended period. Low pressure 
will approach from the west toward the end of the forecast 
period. Latest GOES EAST Geocolor satellite images show clouds 
with cold tops over the northern waters with lightning mostly 
over the central waters near the low. Latest NCEP weather map has
low pressure 998 MB over the Mid Atlantic states with its front 
stretching east across the central waters. Pressure gradient is 
fairly tight over the central waters and winds there are in the 
gale force range.

Seas are relatively large in the east quadrant of the low with a
peak at 14 ft. Otherwise seas range between 6 and 12 ft over the
central and southern waters and they range between 3 and 6 ft 
north of 40N. NWW3 fits well the observed seas pattern and has 
been quite consistent. ECMWFWAVE also fits well the latest 
observations and is in a good agreement with NWW3 in the short 
term on keeping seas relatively large over the southern waters 
with peaks over the central waters. Both wave models agree on 
building seas in ft to the mid 20s over the Baltimore Canyon in 
the short term. Will keep consistency and go with a 50-50 blend 
of the two wave models.

At 500 MB, an upper level trough with significant energy dips 
south from Canada into the far southeastern states. This energy 
will move east across the waters and that will strengthen the 
resultant surface low pressure in the short term. A weak and 
shallow amplitude upper level ridge will then follow. Toward the 
end of the forecast period, another trough with some energy will 
approach the waters from the west and that will strengthen low 
pressure that will approach the waters. As such, pressure 
gradient will initially remain tight with gale force winds. Then,
a relaxed pressure gradient will allow winds to diminish into 
the extended period. Both GFS and ECMWFHR have a good handle on 
the track of the low pressure but they just have small 
differences on the strength of the winds. Will favor GFs 
initially but will switch to ECMWF in the extended period. 


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PREVIOUS DISCUSSION...

The GOES visible satellite imagery shows an area of developing 
low pressure near the Virginia Capes, along with a cold front 
extending to the SE and S from the low over the srn and central
NT2 offshore waters. The lightning density product along with 
the satellite imagery also indicates showers and tstms along the
boundary E of the Virginia Capes. The 12Z models indicate 
conditions will be conducive for convective activity over the 
for the short range, so planning on keeping mention of scattered
showers and tstms in the next forecast. Otherwise, the Ascat 
wind retrievals from 15Z this morning indicated up to 35 kt 
ahead of the frontal boundary, with the highest winds over the
Gulf Stream. Current surface reports only indicate up to 30 kt 
along the coast, though the 12Z GFS and ECMWF winds indicate all
of the observations are not in the areas where the highest winds
were expected at 18Z. The GFS and ECMWF both indicate gales for
tonight in the offshore waters as the low moves N while
strengthening, then moves off to the N by Fri night while strong
cold advection moves over the offshore waters and slowly
increases the winds with the highest over the Gulf Stream. The
12Z models are now in fairly good agreement on the track and 
development of this system, so confidence in the previous gale 
headlines is above average since there is a strong signal in the 
guidance for them. As a result, am planning on starting out with
the 12Z GFS which is well supported by the 12Z guidance. However,
will be using first sigma winds over unstable areas to account
for the deeper mixed layer. Will also be continuing the gales
into Sat night as was done earlier. 

The 12Z models then start diverging late Sun into Mon with the 
next frontal system moving off the New England coast. There have 
been some slight timing differences on the front, with the 
GFS/ECMWF in relatively decent agreement though the GFS is a tad
faster than the rest of the guidance. However, the 12Z models 
then diverge on the development of a low along the front late Mon
and Tue, with a fair amount of model spread on the development.
The GFS has been about the most consistent on the development,
though is much stronger than the rest of the guidance. The GFS is
showing a strong signal for gales, but confidence remains low
since there is not much support. As a result, will stay near the
12Z ECMWF in the medium range period since the ECMWF was
preferred in the previous forecast. However, confidence is low as
a result of the spread. 

.SEAS...The 12Z Wavewatch and ECMWF WAM are initialized within a
ft or two of each other, and agree fairly well over the short
range. Will use a 50/50 blend as a result. Will then stay closer
to the 12Z ECMWF WAM starting Sun to reflect the preference of
the 12Z ECMWF winds.

.EXTRATROPICAL STORM SURGE GUIDANCE...The 12Z ESTOFS indicate a
little over a ft along the mid Atlc and New England coasts
tonight into Fri with the strong easterly flow ahead of the
developing low. The ESTOFS seems a little more reasonable than 
the ETSS which is nearly 50 percent less than the ESTOFS. 
Consult your local National Weather Service office for more 
detailed information. 


.WARNINGS...Preliminary.

.NT1 New England Waters...
.ANZ800...Gulf of Maine...
     Gale tonight into Friday. 
.ANZ805...Georges Bank west of 68W...
     Gale tonight into Saturday. 
.ANZ900...Georges Bank east of 68W...
     Gale tonight into Saturday. 
.ANZ810...South of New England...
     Gale Friday into Saturday. 
.ANZ815...South of Long Island...
     Gale Friday into Saturday. 

.NT2 Mid-Atlantic Waters...
.ANZ820...Hudson Canyon to Baltimore Canyon...
     Gale tonight into Saturday. 
.ANZ915...Hudson Canyon to the Great South Channel...
     Gale tonight into Saturday. 
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale tonight into Saturday. 
.ANZ905...The Great South Channel to the Hague Line...
     Gale tonight into Saturday. 
.ANZ910...East of the Great South Channel and south of 39N...
     Gale tonight into Saturday. 
.ANZ825...Inner Waters from Baltimore Canyon to Cape Charles Light...
     Gale tonight into Friday night. 
.ANZ828...Inner Waters from Cape Charles Light to Currituck Beach Light...
     Gale tonight into Friday night. 
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Gale tonight into Saturday. 
.ANZ830...Inner Waters from Currituck Beach Light to Cape Hatteras...
     Gale Friday night.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale tonight into Friday night. 
.ANZ835...Inner Waters from Cape Fear to 31N...
     Gale tonight.
.ANZ935...Outer Waters from Cape Fear to 31N...
     Gale tonight into Friday. 

$$

.Forecaster Musonda/Kells. Ocean Prediction Center.

 

 



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