marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 323 am EDT Fri Oct 21 2016
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.
The current GOES infrared satellite imagery shows a broad area of low pres just NE of the Bahamas...moving N...and the lightning density product shows some scattered showers and tstms to the N and E of the center. The the NHC tropical weather outlook from 2 am EDT indicates that the low has a 50 percent chance of developing into a tropical cyclone over the next 2 days. The 00z model guidance shows the system moving N...passing just E of the srn and central nt2 waters today into tonight...before passing through the far NE nt2 waters late tonight into Sat. However...the water vapor imagery shows that the will move into a drier air mass to the N of center...which could inhibit development. As far as the models are concerned with this system...there are some small timing differences between the GFS/Gem and the ECMWF/UKMET...but overall confidence is fairly high on the overall track. The previous forecast had gales E of the offshore waters in the southerly flow to the E and se of the low center...mainly limited to the unstable environment over the Gulf Stream. This seems reasonable...so planning on keeping it in the grids for the next package.
The water vapor satellite imagery also shows a strong upper trof inland...as a shortwave trof currently moving into the Mississippi Valley region is carving it deeper. The latest NCEP surface analysis shows an associated strong frontal boundary moving into the ern conus...with a temp gradient near 15 degrees f across it. The 00z models all indicate the front will move offshore this afternoon into tonight...as the upper trof takes on a negative tilt. The GFS has backed off some on the intensity of the cold air behind the front...though very strong cold advection is still shown moving into the offshore waters Sat into sun. The models all indicate a small area off the SC coast by 00z tonight that will fall under the influence of the cold advection...as the right entrance region of a jet streak lines up over it. Model sounding data shows the mixed layer will reach up to 850 mb by 00z tonight...with mixed layer winds near gale force. As a result...planning on adding a brief period of gales off the SC coast for 00z tonight...with moderate to high confidence. Further N...the nrn nt2 and nt1 waters will be impacted by the same cold advection by Sat...and the 00z GFS/ECMWF/UKMET/Gem/NAM all indicate gales across the area. The models are also showing negative static stability over the area impacted by the cold advection...and the 00z GFS/NAM model soundings show the mixed layer will extend up to 850 mb...with Max mixed layer winds to 45 kt just se of Nantucket Island. As a result...planning on using 00z GFS first sigma layer winds to account for the deeper mixing expected...with the highest over nt1...since the GFS is supported fairly well by the rest of the 00z models.
Otherwise...the 00z models all indicate an upper low will form and stall over se Canada. The upper low will continue through the remainder of the forecast period...and keep the offshore waters under the influence of the cold air advection. In addition...the models indicate another shortwave will move through the base of the trof into nt1 and nt2 Mon and Mon night...and deliver a second surge of cold air through the region. The 00z GFS agrees fairly well with the UKMET and Gem on the track of the associated surface low pres system...although the 00z ECMWF is slightly N of the GFS. The previous forecast had gales associated with the second cold surge...which looks reasonable given the good model agreement...so planning on maintaining the previous warning in the next package. Will otherwise be following the 00z for the remainder of the forecast period as it is in reasonably good agreement with the rest of the 00z models.
Seas...the 00z wavewatch and ECMWF wam are both initialized well in the offshore waters. The models are in somewhat decent agreement in the short range...but diverge slightly in the extended...mainly due to slight differences from the associated weather models. Planning on following the 00z wavewatch. However...will be adjusting seas higher in the cold advection tonight off the se coast as winds are above model guidance. Will also be boosting seas over the N portion to account for the strong cold advection.
.Extratropical storm surge guidance...N/A.
.Nt1 New England waters... .anz800...Gulf of Maine... gale Sat into Sat night. Gale possible sun into Sun night. .Anz805...Georges Bank west of 68w... gale Sat into Sat night. Gale possible sun into Sun night. .Anz900...Georges Bank east of 68w... gale Sat into Sat night. Gale possible sun into Sun night. .Anz810...South of New England... gale Sat into Sat night. Gale possible sun. .Anz815...South of Long Island... gale Sat into Sat night. Gale possible sun.
.Nt2 mid-Atlantic waters... .anz820...Hudson Canyon to Baltimore Canyon... gale Sat into Sat night. Gale possible sun. .Anz915...Hudson Canyon to the great South Channel... gale Sat into Sat night. Gale possible sun. .Anz920...Baltimore Canyon to the great South Channel... gale Sat into Sat night. Gale possible sun. .Anz905...The great South Channel to the Hague line... gale today. Gale Sat into Sat night. Gale possible sun. .Anz910...East of the great South Channel and south of 39n... gale tonight into Sat night. Gale possible sun. Gale possible Mon. .Anz835...Inner waters from Cape Fear to 31n... gale tonight. .Anz935...Outer waters from Cape Fear to 31n... gale tonight.
.Forecaster Kells. Ocean prediction center.