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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 161321

Area Forecast Discussion
National Weather Service Honolulu HI
321 AM HST Sun Dec 16 2018

Dry and pleasant conditions associated with high pressure will hold
into the start of the upcoming week. Trade winds will gradually
trend down through Monday, potentially becoming light enough for
land and sea breeze conditions for a brief period late Monday
through early Tuesday for some portions of the state as a weak
cold front approaches and moves into the area. The front is
forecast to quickly advance down the island chain late Tuesday
through Wednesday, bringing increasing rain chances. Gusty
northerly winds along with drier and cooler conditions will follow
Wednesday through Thursday. A return of a more typical trade wind
pattern will be possible Friday into next weekend.


Short-term (through Monday night) guidance remains in good agreement
and reflects the dry pattern holding through Monday due to deep
layer ridging and a strong subsidence inversion. Precipitable water
values are forecast to range from three quarters of an inch to
around an inch, which is below average (drier) for this time of
year. After a long stretch of breezy to windy trades, the pressure
gradient is forecast to relax over the state as a weak cold front
and upper trough approach from the northwest. Trades will respond
and gradually trend down, potentially becoming weak enough for
localized land/sea breezes late Monday through Monday night.

For the extended (Tuesday through Friday), guidance remains in
decent agreement through midweek and shows the aforementioned cold
front advancing down the island chain beginning late Tuesday for
Kauai, then clearing the Big Island by the end of the day Wednesday.
A slight increase in moisture (albeit shallow) combined with this
boundary and upper trough will support increasing rain chances,
especially late Tuesday through Wednesday, as the boundary moves
down the island chain. Breezy northerly winds along with much
drier conditions will follow its passage Wednesday through
Thursday. Dewpoints are forecast to dip into the upper 50s for
the smaller northwest islands. High temperatures may struggle to
reach the 80 deg mark Wednesday afternoon. The dry and pleasant
conditions will likely hold into the second half of the week with
a return of a more typical trade wind pattern by the weekend.

Winds at the summits of the Big Island have mostly remained below
advisory levels overnight, except for a few observations that
neared criteria. A gradual downward trend is anticipated through
the day today.


A strong ridge of high pressure north of the Hawaiian islands
will continue to generate moderate, mostly dry trade winds across
the state. Shower activity should be limited to windward slopes
and coasts. Isolted MVFR ceilings possible in passing showers,
otherwise VFR conditions are expected to prevail.

AIRMET Tango remains in effect for TEMPO moderate turbulence
southwest of all island mountain chains across the Big Islands and
Maui County.


High pressure to the north will maintain moderate to locally
strong trade winds through tonight. A front approaching from the
northwest will shift the high further to the east, which will
decrease the trades some for Monday. The front is expected to
begin impacting the northwest waters around Kauai on Tuesday, and
pushing down the island chain reaching the waters around Big
Island Tuesday night. Strong north winds are expected with and
behind the frontal passage. High pressure is expected to return
northeast of the state for the end of the week.

The new long-period northwest swell reached buoy 51101 to the
northwest of the islands overnight, a bit smaller than expected,
and a few hours delayed. The Hanalei Bay buoy has started to
show this as well, so have lowered swell and wave height grids to
better account for the buoy observations. The forecast reflects
low end Small Craft Advisory (SCA) for the coastal waters through
tonight due to a combination of winds and seas.

Surf is still expected to rise today, so the High Surf Warning
for north and west facing shores of Niihau, Kauai, Oahu, Molokai,
and north facing shores of Maui and High Surf Advisory for north
facing shores of the Big Island remains in effect through tonight.
However with the swell coming in lower than expected, have
lowered the surf heights.

An even larger northwest swell is expected to build late Monday,
peaking well above warning levels Tuesday night. Exposed coastal
waters will once again rise to over 10 feet as these swells come
rolling through. This new swell, coupled with the increasing winds
behind the above mentioned front, will likely lead to a SCA for
most, if not all, waters into midweek.

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


High Surf Warning until 6 AM HST Monday for Niihau-Kauai
Windward-Kauai Leeward-Waianae Coast-Oahu North Shore-Oahu
Koolau-Molokai-Maui Windward West-Maui Central Valley-Windward

High Surf Advisory until 6 AM HST Monday for Big Island North
and East.

Wind Advisory until noon HST today for Big Island Summits.

Small Craft Advisory until 6 AM HST Monday for all Hawaiian




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

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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
Send comments to: Ryan Lyman