High Wind in Washington, October 14, 2016

Area Forecast Discussion
National Weather Service Seattle WA
929 PM PDT Thu Oct 13 2016

.SYNOPSIS...Wet weather will continue and it will become windy
tonight as a strong low pressure system tracks toward the north
Washington coast. Friday will be wet and windy as the low weakens
over British Columbia. There will be a lull in the weather Friday
night and Saturday morning. A powerful storm is likely to reach
the area Saturday evening.

&&

.SHORT TERM...The first in a pair of strong Pacific storm systems
will continue to impact Western Washington tonight. The main
concern will be strong wind, especially along the coast. The
Oregon coast is seeing gusts of 50 to 70 mph as a strong front
moves inland. This is just about to reach the north and central WA
coast. The Seattle metro will see a burst of wind from now through
late tonight with gusts of 35 to 50 mph possible. This complex
system will send a second, strong surface low inland Friday
afternoon which may bring another round of high wind to the coast
and north interior - the High Wind Warning will be extended.

Models are starting to line up for the very strong system moving
inland on Saturday. As mentioned before, this system contains
remnants of Typhoon Songda and will rapidly deepen to around 970
mb off the Pac NW coast before moving inland Saturday night. The
latest models show the low moving inland over the central or north
WA coast then tracking NE into southern B.C. This tracking would
bring high wind to all areas of Western Washington, including the
Seattle area, with damaging winds possible. Some of the mesoscale
models are showing gusts to 60 to 70 mph in the interior. Overall,
confidence is higher that we will reach high wind across much of
the area. Stay perched. 33

Coastal flooding is a concern on Saturday and Saturday night. First,
very low air pressure will help to draw sea level up by 2 or 3
(possibly more) feet due to the extremely low atmospheric pressure.
Would take a 2.5 to 3-foot tidal surge at Seattle to reach minor
tidal overflow levels. Along the coast, it appears the lowest
atmospheric pressure will coincide more closely with low tide early
Saturday evening, but there are still concerns for the preceding and
proceeding high tides in the early afternoon and overnight Saturday
night. For the Saturday night high tide, the astronomical tide will
be nearly 3 feet below minor tidal overflow levels, but any residual
anomaly combined with onshore winds and 20-foot waves along the
Grays Harbor County coastline could present coastal flooding
problems. The good news is that today's revised storm track will
keep the bigger waves further south along the Oregon coast, but the
bad news is that it still may not be enough to preclude coastal
flooding. A Coastal Flood Watch may need to be issued late tonight
for Saturday and Saturday night. Haner

.LONG TERM...The 6-10 day outlook is calling for above normal
temperatures and above normal precipitation, and I think the weather
may transition for cool and showery early in the week to mild and
wet for the second half of the week. The GFS looked like it could
give us a dry day next Wednesday, but the ECMWF was wet and the
extended forecast probably has little value today.

&&

.HYDROLOGY..A flood warning is in effect for the Skokomish River in
Mason county. Some of the more flood-prone rivers running off the
west slopes of the Cascades are also at risk, especially the
Nooksack River in Whatcom County and the Stillaguamish River in
Snohomish County. A flood watch is in effect for those two counties.
Both the system tonight and the one for the weekend have high
precipitable water. Keep an eye on your favorite river's forecast.

&&

.AVIATION...Moist Pacific frontal systems will bring rain to W WA
through Saturday and likely into Sunday as well. The rain may seem
nearly continuous at times but there will be waves moving across W
WA from this complex system, which will produce lulls where the rain
may briefly taper off or end. The first front is still expected to
move across the W WA interior around 09Z with the secondary surface
low moving NE over Vancouver island about the same time. The main
surface low farther offshore will move over Vancouver island Friday
afternoon. Waves embedded in the SW flow aloft over the area will
keep rain going at times behind the front through Friday.

Surface and low level winds will also be quite strong and gusty at
times ahead of and behind this initial front and the associated low.
Current models suggest that gusts will continue Friday as the main
low crosses Vancouver island. Ceiling and visibility conditions will
be predominantly IFR and MVFR the next few days.

KSEA...The moist Pacific frontal system will produce IFR/MVFR
conditions for the next few days along with periods of gusty winds.
A front will move across Puget Sound around 09Z. Low level winds
around FL050 will rise to S50-70KT around 02Z and continue until the
front passes around 09Z. Surface winds will be SE 10-15KT through
04Z then shift S 20G35KT from 04Z-09Z. Kam/SMR

&&

.MARINE...Two big storms on the horizon. The first is actually a
pair of conjoined surface lows that will impact the coastal waters
tonight and into the overnight hours while spreading eastward.
Current observations show that highest wind speeds still down south
of the CWA...but again the expectation is for those winds to move
north over the area overnight. The highest winds will follow these
lows as it moves northward through the night. Models remain
consistent on gradients and wind speeds...so will leave inherited
forecast and Storm Warning alone for evening forecast package.
Previous model runs had suggested that winds would ease on
Friday...but current models seem to be shying away from that
solution. While winds may subside somewhat...Friday may end up being
still rather blustery.

Next big storm coming late Saturday or Saturday night in the form of
a low that will peak in strength as a very deep low off the coast.
Models still in some disagreement as to the track of this particular
storm as it could either move across the northwest tip of Washington
or on a track up Puget Sound. This should be viewed as a potentially
dangerous storm. Storm-force winds seem likely over the coast and
the North Interior waters. If the low follows a worst-case track,
then Puget Sound could get storm-force winds as well. Will monitor
this closely as 00Z data comes in and update accordingly for
early morning forecast package. Haner/SMR

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...High Wind Warning until 7 AM PDT Friday for Bellevue and
     Vicinity-Bremerton and Vicinity-East Puget Sound Lowlands-
     Everett and Vicinity-Hood Canal Area-Lower Chehalis Valley
     Area-Seattle and Vicinity-Southwest Interior-Tacoma Area.

     High Wind Watch from Saturday afternoon through late Saturday
     night for Admiralty Inlet Area-Bellevue and Vicinity-
     Bremerton and Vicinity-Cascades of Pierce and Lewis
     Counties-Cascades of Snohomish and King Counties-Cascades
     of Whatcom and Skagit Counties-Central Coast-East Puget
     Sound Lowlands-Eastern Strait of Juan de Fuca-Everett and
     Vicinity-Hood Canal Area-Lower Chehalis Valley Area-North
     Coast-Olympics-San Juan County-Seattle and Vicinity-
     Southwest Interior-Tacoma Area-Western Skagit County-
     Western Strait of Juan De Fuca-Western Whatcom County.

     Flood Watch through Friday afternoon for Bellevue and Vicinity-
     Cascades of Snohomish and King Counties-Cascades of Whatcom
     and Skagit Counties-East Puget Sound Lowlands-Everett and
     Vicinity-Western Whatcom County.

     High Wind Warning until 3 PM PDT Friday for Admiralty Inlet Area-
     Central Coast-North Coast-San Juan County-Western Skagit
     County-Western Whatcom County.

PZ...Small Craft Advisory for rough bar until 5 PM PDT Friday for
     Grays Harbor Bar.

     Storm Warning until 3 AM PDT Friday for Coastal Waters From Cape
     Flattery To James Island 10 To 60 Nm-Coastal Waters From
     Cape Flattery To James Island Out 10 Nm-Coastal Waters From
     James Island To Point Grenville 10 To 60 Nm-Coastal Waters
     From James Island To Point Grenville Out 10 Nm-Coastal
     Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-
     Coastal Waters From Point Grenville To Cape Shoalwater Out
     10 Nm.

     Gale Warning until 3 PM PDT Friday for Admiralty Inlet-East
     Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland
     Waters Including The San Juan Islands-Puget Sound and Hood
     Canal.

     Gale Warning until 9 AM PDT Friday for West Entrance U.S. Waters
     Strait Of Juan De Fuca.

     Gale Warning until 3 AM PDT Friday for Central U.S. Waters
     Strait Of Juan De Fuca.

&&

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