marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 1007 PM EDT Wed Jun 20 2018
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.
The GOES infrared satellite imagery and the lightning density product show an area of showers and tstms along the coast of North Carolina, just S of a weak frontal boundary over the central nt2 offshore waters. Previous weather grids had an area of showers and tstms, so planning in making adjustments to match up with the current conditions. Otherwise, current surface observations indicate winds up to 20 kt in the offshore waters with the highest in the Gulf of Maine ahead of another weak cold front moving towards the area from the NW. Winds are lighter across nrn nt2 and srn nt1 with a weak ridge extending over the area to the N of the aforementioned front over central nt2. The 18z GFS and 12z ECMWF winds are initialized well when compared with the data, and the models indicate that the front over central nt2 will weaken as the second weak front over New England moves into the area tonight into Thu. The models also indicate a weak low pressure center will move off the Delmarva Peninsula late tonight into Thu, and pull another weak cold front over the area. The GFS/ECMWF agree fairly well on the synoptic features with only minor timing and intensity differences. The previous forecast started out with the 12z ECMWF, so planning on staying near it as the 18z guidance is supporting the previous grids.
The models then remain in decent agreement on the synoptic features into Sat night, before some differences begin developing between the models on the track and timing of a series of low pressure centers through the W Atlc through the remainder of the forecast period. The 12z ECMWF is somewhat near the 12z GFS, but the 18z run trended S, and closer to the 12z Gem. The ECMWF is also slower than the other global models towards the tail end of the forecast period on late sun and Mon, but no clear consensus is evident in the guidance as all solutions are different from each other. The gefs ensemble members are showing no clear signal with regards to the lows, so confidence is generally low in the guidance in the medium range. The previous forecast stayed with the 12z ECMWF through the remainder of the forecast period, so will stay with it in the update package mainly to stay near continuity. However, the models are in good agreement that the winds will remain below 34 kt over the entire forecast period, so confidence is high with maintaining no warning headlines in the update package.
----------------------------------------------------------------- Previous discussion...
Current conditions...the 12z NCEP surface analysis shows a stationary front bowing roughly E to W across the central nt2 waters into the Cape Henry region. Otherwise, the analysis indicates weak high pressure ridging over the offshore waters. Latest available ascat and ascat hi-res passes from a few hours ago indicates 5 to 15 kt winds across the offshore waters. Lightning density product data at 1840z shows a line of scattered showers and tstms along the cold front in the outer zones of the central nt2 waters.
Models/forecasts...the 12z medium range models are in good overall agreement across the offshore waters for tonight into sun. The 12z CMC is showing large timing differences for the Mon and Mon night timeframe, while the 12z UKMET is significantly faster than the other models with the cold front on Mon and Mon night, and the 12z ECMWF/GFS area showing the best agreement for late sun through Mon night. Will use the 12z ECMWF for the wind grids over the entire forecast period, since it is still showing very good run to run consistency and has good support from the latest wpc medium range forecaster guidance. With the except of the 12z CMC near the end of the forecast period, all of the models indicate that the winds will remain at below gale force through Mon night, so confidence is very good for no hazard grids during the forecast period. Am not planning to make any significant changes to the current model trend at this time.
Seas...the 12z emcwf wam and 12z wna wavewatch both initialized well over the coastal and offshore waters versus the latest buoy observations and altimeter data, with seas 5 ft or less over the offshore waters. The models are in good agreement through the forecast period, with only a few minor differences noted mainly during the Fri into Sat timeframe. Will go with a 2:1 blend of the 12z ECMWF wam/wna wavewatch to smooth out the model differences while maintaining consistency with the preferred 12z ECMWF wind grids.
Extratropical storm surge guidance...N/A.
.Nt1 New England waters... None.
.Nt2 mid-Atlantic waters... None.
.Forecaster Kells/Scovil. Ocean prediction center.