Marine Weather for HS 100


marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 919 am EDT Thu Apr 27 2017

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

GOES visible satellite imagery and the lightning density product indicate an area of showers and tstms along a weakening cold front across the nrn nt2 and nt1 offshore waters. Ascat winds from 02z last night indicated gales to the se of the nrn nt2 waters over the Gulf Stream and up to 30 kt in the offshore waters. Current surface observations indicate the strongest winds have moved east of the offshore waters, and the 06z GFS shows up to 25 kt over far NE nt2 and se nt1 and diminishing as the front weakens while drifting to the east. The 00z ECMWF/UKMET/Gem/NAM all agree well with the GFS on the timing and weakening trend, so planning maintaining previous grids with this system which were based on the 00z GFS. Also planning on adding mention of showers and tstms in the update package.

Otherwise, the models remain in good overall agreement throughout the remainder forecast period on the overall pattern, although the 06z GFS continues to be a fast outlier with the warm front on Mon. In addition the GFS/Gem are showing gales ahead of the associated cold front later on Mon, though the Gem extends them over the cold shelf waters where shallower vertical mixing can be expected. The 00z ECMWF/UKMET are weaker and indicate 25 kt with a small area of 30 kt. The ECMWF is also weaker with the low level jet, so confidence with the gales on Mon remains below average. The previous forecast followed the 00z ECMWF and capped winds at 30 kt. This still looks good, so planning on staying with previous grids through the mediun range.

----------------------------------------------------------------- Previous discussion...

Summary...the 00z NCEP surface analysis shows a 1008 mb low centered near New York City, with an occluded front extending E from the low across Long Island Sound, and an associated cold front extending S and SW across the ern nt2 waters. The analysis also indicates a strong high pres ridge building W towards the offshore waters and resulting in a strong pres gradient between the cold front and the ridge. Latest available ascat hi-res and ascat passes from 02z show 20 to 30 kt winds over the NE part of the nt2 waters, with a swath of 10 to 20 kt winds in the Georges Bank and Gulf of Maine waters. Lightning density product data at 0650z shows an area of scattered showers and tstms over the NE nt2 waters E of 70w.

Models...the 00z medium range models are in good agreement across the offshore waters for today through Sat, so will be using the representative 00z GFS 10m/30m solution with the stability smart tool for this timeframe. The 00z GFS is faster than the other models with the warm front Mon and Mon night, and is also stronger than most of the models with the S to SW flow ahead of the cold front for later Mon and Mon night. Will use the 00z ECMWF for Sat night through the rest of the forecast period, since it has good support from the 00z UKMET and the latest wpc medium range forecaster guidance.

Seas...the 00z wna wavewatch and 00z ECMWF wam both initialized well over the coastal and offshore waters. The models are in good agreement for today through Sun night, with only minor differences noted, so a 50/50 blend of the 00z wavewatch/wam will be used for the sea height grids during this timeframe to smooth out the differences. The 00z ECMWF wam will be used exclusively for Mon through the rest of the forecast period, since the 00z ECMWF is the preferred model for this timeframe.

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


.Nt1 New England waters... None.

.Nt2 mid-Atlantic waters... None.


.Forecaster Kells/Scovil. Ocean prediction center.

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