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222
AGNT40 KWNM 190208
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
1010 PM EDT WED 18 SEP 2019

.FORECAST DISCUSSION...Major features/winds/seas/significant
.weather for the North Atlantic Ocean W of 50W from 30N to 50N.

With strong high pressure anchored near the New England and
northern/central Mid-Atlantic coasts this evening through the
end of the week, strong to gale force northeast winds well
northwest of Hurricane Humberto are likely to persist across the
northern outer NT2 zones at least into Thu evening. The latest
models remain tightly clustered with the forecast track for
Humberto through the short term. Recent GOES-16 imagery suggests
that Humberto is beginning to take on some extratropical
characteristics as it becomes more asymmetric, and the 00z
surface analysis shows the baroclinic zone encroaching into the
northern periphery of the hurricane. Humberto will likely
complete extratropical transition Thu night or early Fri while
centered about 400 nm southeast and east of Georges Bank.
Elsewhere across the offshore waters, high pressure will be the
dominant feature as it slowly moves off the Mid-Atlantic coast
this weekend with the ridge persisting across the NT2 waters
through early next week. During the medium range, a cold front
is expected to approach the New England coast late Sun through
Mon, and move offshore Mon night or Tue. The previous OPC wind
grids generally appear representative through the period. We
will only be making modifications through the near term to
account for any subtle changes in the updated NHC forecast for
Humberto. Offshore buoy reports indicate the 12 ft wave heights
extend further west and southwest of the center of Hurricane
Humberto than shown by the Wavewatch or ECMWF WAM guidance this
evening.

---------------------------------------------------------------
...Previous Discussion...

Per the 18Z NCEP surface analysis a stationary front was located
across the far southern NT2 waters roughly along 31N-32N. High
pressure centered over eastern Canada and New England, extended
its ridge down through the NT1 waters and into the rest of the
NT2 waters. At 21Z Hurricane Humberto was located E of the SE
NT2 waters near 33.0N 66.3W. GOES-East satellite data revealed
showers and thunderstorms over parts of the outer central and
southern NT2 waters, mainly in association with Humberto. The
latest ASCT hires data revealed 15-25 kt over the NT1 waters,
with 20-30 kt across the NT2 waters. 25-35 kt winds were located
over parts of the outer central and southern NT2 waters, which
matches fairly well with the ongoing forecast.

I will continue with the existing girds through Fri 06Z, with
edits made as needed based on the 2100Z NHC advisory for
Hurricane Humberto. In the short term Humberto will continue
moving E, then NE and away from the region. The building high
from the N will interact with Humberto allowing for a strong
pressure gradient across the region through Thu night with a
wide area of 20-30 kt winds over much of the NT1 and NT2 waters.
Gales, confirmed by the latest ASCT hires data, will remain in
the forecast over parts of the outer NT2 waters through Thu
night due to this strong pressure gradient. From Fri 12z on, I
will populate the grids using the 12Z ECMWF as model agreement
is fairly decent through Mon 12Z concerning the synoptic
pattern. Winds ease to less than 20 kt or so by Fri as the high
moves overhead, with winds increasing again, mainly over the N
NT2 waters into the NT1 waters as a front approaches from the NW
Sun night, then moves into the NT1 and N NT2 waters by the end
of the period on Mon.

.SEAS...I will continue with the existing grids through Fri 06Z
given the choice to maintain the existing winds grids, then
transition to the 12Z ECMWF through Mon 12Z given the choice to
continue with the 12Z ECMWF winds at that point. For the rest of
the period after Mon 12Z I will let the existing grids remain in
place.

.EXTRATROPICAL STORM SURGE GUIDANCE...The 12Z ESTOFS indicates a
surge of a 0.5-1 feet tonight into Thu along the Mid-Atlantic
coast down into the SE coast with the persistent NE fetch to the
NW of a front with strong high pressure building over the area.
Surge associated with Humberto should be E of the area as the
system continues moving to the NE. However, see the forecast
from your local NWS forecast office for more information
regarding the effects from both Humberto and the strong NE winds
expected over the area over the next few days.

.WARNINGS...Preliminary.

.NT1 New England Waters...
     None.

.NT2 Mid-Atlantic Waters...
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale tonight.
.ANZ905...The Great South Channel to the Hague Line...
     Gale tonight into Thursday night.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale tonight into Thursday.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras
Canyon...
     Gale tonight.

$$

.Forecaster Clark/Holley. Ocean Prediction Center.



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