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NOAA>NWS>NCEP>OPC>Marine>Atlantic>Offshore>North Atlantic Marine Weather Discussion

North Atlantic Marine Weather Discussion

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AGNT40 KWNM 250727

.Marine Weather Discussion for N Atlantic Ocean 
.NWS Ocean Prediction Center Washington DC 
215 AM EDT Sat 25 Mar 2017 

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

The most recent Ascat overpasses across the offshore waters from 
0050Z to 0230Z indicated southwest winds to 30 kt across the 
northern NT2 zones and to 25 kt elsewhere north of Hatteras 
Canyon. Although the most recent model guidance all initialized 
some winds to 30 kt, Ascat shows more widespread 30 kt than 
initialized. However, the higher 00Z GFS first sigma level winds 
are too high. As a result, and after some testing some different 
model blends, came up with a 2:1 00Z GFS first sigma level and 
00Z ECMWF boundary layer wind blend that best matched the Ascat. 
At 06Z the cold front had moved off the New England coast and 
the 00Z models are in good agreement that the front will slowly 
move south across the NT1 and northern NT2 waters today into 
tonight, before stalling off the Delmarva peninsula late tonight 
into early Sunday. Models are also consistent that the west to 
southwest widns south of the cold front will gradually diminish 
through the day today, to less than 25 kt later this evening. 
Then as high pressure builds off the New England coast tonight 
into Sunday night, the 00Z GFS/NAM/Canadian are somewhat 
stronger than the 00Z ECMWF/UKMET with the easterlies just 
poleward of the stationary front across the southern NT1 and 
northern NT2 waters Sunday into Sunday night. This discrepancy 
in the models' wind speeds north of the front persists late 
Sunday night into Monday night as the front lifts northeast back 
across the NT1 waters as a warm front. OPC preference continues 
with these slightly higher winds to 25 kt. For wind grids will 
use the blend noted above through tonight, before transitioning 
to the 00Z GFS Sunday through Monday. 

In the medium range, the 00Z models diverge greatly with a 
series of weak upper shortwaves moving through the northeastern 
US and off the northern mid Atlantic and/or New England coasts 
Tuesday night and Wednesday. The GFS has been consistently 
stronger with the associated developing low and cold front 
forecast to move offshore late Tuesday and Wednesday. There also 
continued to be farily widespread differences with the timing of 
this system. The 00Z models then become more consistent later 
Wednesday night into Thursday that the aformentioned shortwaves 
and approaching northern stream trough will consolidate into an 
upper low across southeastern Canada and Maritimes. Given model 
discrepancy, have decided to use a blend of the 00Z GFS and 00Z 
ECMWF for wind grids Tuesday night through Wednesday night, 
which offers a compromised timing with the front. However did 
adjust these blended winds upward by about 10 percent to get 
some associated winds to 25 kt.  We have above average forecast 
confidence that winds across the NT1 or NT2 offshore waters 
should remain below gale through at least midweek. 

.Seas...The 00Z Wavewatch III is slightly better initialized 
than the 00Z ECMWF WAM with wave heights across the west 
Atlantic this morning. However, the 00Z WW3 may not be high 
enough across the nothern NT2/southern NT1 zones where there are 
still some 30 kt winds occurring. Am preferring to use an even 
blend between this guidance through the forecast period. 

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


.NT1 New England Waters... 

.NT2 Mid-Atlantic Waters... 


.Forecaster Clark. Ocean Prediction Center.

NOAA/ National Weather Service
National Centers for Environmental Prediction
NOAA Center for Weather and Climate Prediction (NCWCP)
Ocean Prediction Center
Mr. Darin Figurskey
Chief, Ocean Forecast Branch
5830 University Research Court
College Park, Maryland 20740-3818

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Page last modified:  Monday, July 25, 2016 12:55:54 UTC