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Area forecast discussion 
National Weather Service Honolulu HI
800 PM HST Wednesday Dec 17 2014

Synopsis...
high pressure centered north of the islands will maintain locally
breezy trade winds through Friday. The trades will focus showers
over windward and mountain areas. The winds will become light over
the weekend as the high leaves the area and a front approaches the
islands from the northwest. The front will move down the island
chain between Sunday night and Tuesday night bringing with it some
showery and windy weather.

&&

Discussion...
both the European model (ecmwf) /ec/ and GFS are in good agreement with the timing of
the next weather system to affect the islands...that is a cold
front. The models concur the front will reach Kauai Sunday night and
exit The Big Island late Tuesday night...early Wednesday morning.

The front will be accompanied by some showery weather along with
strong and gusty north and northeast winds. The front will have
some upper level...dynamic support...by ways of a short wave trough
accompanied by a pool of cold air of minus 14 c by the GFS to minus
17 c by the ec. This will most likely result in enhanced
showers...locally heavy rains and even a slight chance of a
thunderstorm.

This assessment will not be reflected in the grids yet...we will
confirm this with several more models runs to see if this trend
continues or the models backs off. We should have a better idea by
Friday.

In the mean time...it will be a moderate to locally strong trade
wind pattern with showers mainly nights and mornings and favoring
the windward and mountain areas. The high centered 700 miles north of
the islands with at 1027 mb value is forecast to move eastward
during the next 72 hours. By about the 60th hour...or Saturday
morning...the high will be out of range where we can finally lower
the Small Craft Advisory.

The models are maintaining a few windward showers but otherwise
rather dry conditions over the weekend while the winds briefly turn
southeast Saturday. On Sunday...the winds will become light and
variable ahead of the approaching front.

&&

Aviation...
clouds and showers moving over mainly windward and Mauka areas will
at times bring MVFR conditions to those areas. Otherwise VFR
conditions are expected to prevail.

High pressure building to the north will strengthen trade winds
Thursday which may require an airmet for mechanical turbulence to
the Lee of the mountains.

&&

Marine...
the trade winds will be winding down during the next couple of days
where the Small Craft Advisory /sca/ can finally be lowered by
Friday night.

As for the swells...a bump from the northwest is expected Thursday evening
where surf heights will come close to or reach advisory levels for
the north and west facing shores of at least Kauai and Oahu. This swell
will be subsiding starting Friday. Then a very large northwest swell will
be arriving Sunday boosting the surf into the warning category for
the north and west facing shores of most islands. The source of this swell
is from a rather broad area of strong low pressure situated off the
East Coast of Japan tonight. A storm low predicted by the models to
form north of the islands the middle of next week may keep surf
elevated in at least the advisory range through Christmas.



&&

Hfo watches/warnings/advisories...
Small Craft Advisory until 600 PM HST Friday for Maalaea Bay...the
waters south of The Big Island...and the pailolo and alenuihaha
channels.

&&

$$
Public/marine...lau
aviation...M Ballard

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