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RH12 %
WindW 10 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

852
FXHW60 PHFO 231938
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
938 AM HST Thu Nov 23 2017

.SYNOPSIS...
High pressure north of the State will keep breezy to windy trades
blowing through the Holiday weekend. Passing showers will favor
windward and mauka areas, with a stray shower reaching leeward
areas from time to time due to the strength of the trades. A wet
trade wind pattern is expected to develop on Sunday and continue
through early next week, as deep tropical moisture moves into the
area from the southeast. The wettest conditions are expected over
the eastern end of the island chain.

&&

.DISCUSSION...
Currently at the surface, a 1034 mb high centered around 1350
miles north-northwest of Honolulu, is driving breezy to windy
trades across the island chain this morning. Satellite imagery
shows mostly cloudy skies across most windward areas, and
generally partly cloudy conditions in leeward locales. Radar
imagery shows scattered showers moving into windward areas, with
the showers also reaching leeward areas from time to time. Main
short term concerns revolve around the rain chances and the
strong trade winds.

Today through Sunday,
Breezy to windy trades will continue right through the Holiday
weekend, as the strong area of high pressure to the north-
northwest of the State gets re-enforced by another strong high
dropping southward from the Aleutian islands. Clouds and showers
will continue to favor windward and mauka areas through the
period, with a stray shower reaching leeward areas from time to
time. Both the GFS and ECMWF show deep tropical moisture lifting
northwestward into the eastern end of the island chain on Sunday,
and this is expected to bring a wet trade wind pattern to Maui
County and the Big Island.

The Wind Advisory for areas over and downwind of the Kohala
mountains on the Big Island, as well as the island of Lanai
remains in effect through 6am Friday. With the strong winds
expected to continue through the weekend, the Wind Advisory may
need to be extended in time.

Sunday night through next Thursday,
High pressure north of the State will keep a moderate to breezy
trade wind flow in place through the period. Model solutions are
in good agreement showing deep moisture lingering over the eastern
end of the State through the first half of next week, so a wet
trade wind pattern is expected over Maui County and the Big
Island. Across Oahu and Kauai, more of a typical trade wind
weather pattern is expected to prevail, but this could change if
the slug of deeper moisture lifts further northward than currently
anticipated.

Additionally, with the deeper moisture overspreading the eastern
end of the State, some snow may fall over the Big Island Summits,
but it's still to early to determine how much.

&&

.AVIATION...
Trade winds will increase to strong levels across the state today,
as high pressure builds northwest of the area. AIRMET Tango remains
in effect for moderate low level turbulence over and downwind of
the higher terrain. AIRMET Tango is also in effect for strong
surface wind speeds for portions of Lanai and the Big Island.

Trade wind showers will be most prevalent over windward
areas, and AIRMET Sierra for mountain obscuration is currently in
effect for windward parts of Maui and the Big Island, where the
showers have been particularly persistent. While some of the
showers will reach leeward areas at times due to the strengthening
trades, expect VFR conditions to prevail there. AIRMET Sierra
could expand to windward sides of Molokai and Oahu later today.


&&

.MARINE...
The very large north swell, combined with strong to near gale
force northeast winds are producing hazardous conditions along
exposed coastlines. A High Surf Warning remains in effect for
north and east facing shores, and will be in effect through Friday
morning, but expect this swell to continue to subside through
Saturday. Buoy reports show this swell has arrived larger than the
models expected. The forecast was modified earlier this morning to
better reflect observations, and further modifications may be
needed today as we monitor the swell.

A new north swell is expected to arrive Sunday, peaking Monday
near advisory levels, then subsiding through Tuesday. Additional
swells are expected to arrive Wednesday.

The current swell and winds are producing Small Craft Advisory
(SCA) level winds and seas over most coastal zones. Trade winds
are expected to remain strong through the first half of next
week. Combined with the new north swell mentioned above that will
keep the seas high, the SCA will likely be extended.

See the latest Oahu Surf Discussion (SRDHFO) for additional
details on surf and swell.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Warning until 6 AM HST Friday for Niihau-Kauai
Windward-Kauai Leeward-Oahu North Shore-Oahu Koolau-Olomana-
Molokai-Maui Windward West-Maui Leeward West-Maui Central Valley-
Windward Haleakala-Big Island North and East.

Wind Advisory until 6 AM HST Friday for Lanai-Big Island North
and East-Kohala.

Small Craft Advisory until 6 AM HST Saturday for all Hawaiian
waters-

&&

$$

DISCUSSION...Jelsema
AVIATION...Foster
MARINE...M Ballard

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office