marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 928 PM EDT Fri Jun 22 2018
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.
The main concern over the offshore waters tonight and tomorrow will be the threat for strong winds near or exceeding gale force and very rough seas in and near any of the thunderstorms that occur over the region, especially near and off the mid-Atlantic coast. The latest GOES-IR imagery, radar imagery and lightning density product data shows a few strong thunderstorms near Norfolk, VA and east of the Delmarva coast extending from near 36n 73w to 38n 69w, or over offshore zones anz925 and 920 moving off to the east and northeast. We will attempt to highlight the potential for the stronger winds in thunderstorms for the evening opc forecast update. These scattered thunderstorms are located along a nearly stationary frontal boundary which extends east and northeastward from just south of Norfolk this evening. High pressure is moving east away from the New England waters. Other- wise, the 18z GFS is very similar to the 12z cycle which was used for the offshore forecast for tonight into early next week. We will make just a few minor adjustments mainly in deference to nearby TAFB and coastal WFO grids and forecast over the next few days, for the evening update.
Seas...sea heights range from around 6 feet north of the stationary front off the Delmarva coast and Jersey Shore, to 2 feet or so over northern New England this evening according to the latest observations and altimeter data. No major changes appear needed to the ongoing forecast for the evening update, with only minor alterations mainly closer to the coastal WFO and TAFB waters to produce a more seamless marine forecast over the region for the next few days.
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Current conditions...the 12z surface analysis shows a 1010 mb low centered 38n 67w, with a stationary front extending W from the low across the central nt2 waters into the Cape Hatteras region. Otherwise, the analysis shows a low pressure trough extending N to S across the Carolinas and into the SW part of the nt2 area, and high pressure ridge over the waters N of the low and stationary front. Latest available ascat ascat hi-res passes from a few hours ago show 20 to 25 kt winds with a few gusts to 35 kt in S to SW flow over the outer zones of the southern nt2 waters, with 20 to 25 kt winds in NE flow across zones 910 and 920 in the northern nt2 waters. Elsewhere across the offshore waters, ascat indicates 10 to 20 kt winds. Lightning density product data at 19z shows scattered showers and tstms along and S of the stationary front over the outer zones of the central and southern nt2 waters.
Models/forecast...the 12z medium range models are in very good overall agreement across the offshore waters for tonight through Sun night, so the representative 12z GFS 10m solution will be used for the wind grids through Sun night. The 12z ECMWF is a significantly fast outlyer regarding a developing low passing E of the offshore waters Mon through Tue, so the slower 12z GFS 10m solution will be also be used for this timeframe in order to maintain continuity. The 12z GFS becomes a slow outlyer for Tue night through Wed night, thus the faster 12z UKMET will be used for the wind grids for this timeframe. Beyond Wed night, will stay with the previous grids to preserve continuity.
Seas...the 12z wna wavewatch and 12z ECMWF wam both initialized well over the offshore waters versus recent buoy observations and altimeter data. Seas in the offshore waters are currently 5 ft or less. The 12z wna wavewatch will be used for the sea height grids for tonight through Tue to match up with the preferred 12z GFS wind grids, before switching to a 50/50 blend of the 12z wavewatch/wam for Tue night through Wed night because the GFS is a not a preferred model for that timeframe. Then will use the previous sea height grids for Thu through the rest of the forecast period to remain consistent with the wind grids.
Extratropical storm surge guidance...N/A.
.Nt1 New England waters... None.
.Nt2 mid-Atlantic waters... None.
.Forecaster Mills/Scovil. Ocean prediction center.