Marine Weather for HS 100


.Marine weather discussion for N Atlantic Ocean .NWS ocean prediction center Washington DC 315 PM EDT Fri 21 Jul 2017

.Forecast discussion...Major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.

This mornings ascat overpasses covered the offshore waters east of about 73w and returned highest winds to 20 kt only across the outer anz905 waters, with winds elsewhere 15 kt or less. The ascat retrievals also showed light winds associated with the weak cold front which has further weakened and should dissipate later this afternoon. The 12z models are in good agreement that a stronger cold front will move off the New England coast tonight, with some differences then showing up as to how quickly and where the front will stall Saturday/Saturday night. The 12z GFS/CMC are slightly south of the 12z ECMWF/UKMET position. The models also differ with the timing/track of multiple surface lows which are expected to track east along the front in the vicinity of 40n sun/Mon. The 12z ECMWF appear too strong with the Sunday low. The 12z GFS 10m winds look reasonable over the next 24 hours, then to account for the detail differences noted above, will populate the opc wind grids with a 50/50 blend of the 12z ECMWF and 12z GFS Saturday night through Sunday night.

By early next week, versus its several previous runs, the 12z GFS finally trended less progressive with the upper level trough moving through the northeastern US Monday and into the nt1 waters Tuesday, and now is more in line with the ECMWF/UKMET and gefs/ECMWF eps means. The 12z models then all indicate that the associated cold front should sweep across the nt1 waters Monday night and the northern/central nt2 waters Tuesday/Tuesday night. The guidance is also consistent that this front will stall off the North Carolina coast Wednesday/Wednesday night as high pressure passes east across the New England waters. Given its much better run to run consistency we are favoring the 12z ECMWF from Monday Onward.

.Seas...Both the 12z wavewatch iii and 12z ECMWF wam were well initialized with wave heights in the W Atlantic this afternoon, which are currently 4 ft or less in the offshore waters. For the wave height grids, used a 50/50 blend of the 12z ww3 and 12z ECMWF wam through Sunday night. Then being similar to what was done with winds, will use a blend more heavily weighted with the 12z ECMWF wam from Monday Onward.

.Extratropical storm surge guidance...N/A.


.Nt1 New England waters... None.

.Nt2 mid-Atlantic waters... None.


.Forecaster Clark. Ocean prediction center.

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