Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 171334
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
334 AM HST Mon Dec 17 2018

.SYNOPSIS...
Dry and pleasant conditions associated with high pressure will
hold through early Tuesday. Trade winds will gradually trend
down, potentially becoming light enough for land and sea breeze
conditions for a brief period tonight through Tuesday for 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 the
upcoming weekend.

&&

.DISCUSSION...
Short-term (through tonight) guidance remains in good agreement
and reflects the dry pattern holding 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 tonight into Tuesday.

For the extended (Tuesday through Saturday), guidance remains in
good 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 a band of clouds
and increasing rain chances late Tuesday through Wednesday as the
boundary moves down the island chain. Breezy northerly winds
along with much drier and cooler 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.

&&

.AVIATION...
An east to west oriented surface ridge north of the Hawaiian
Islands will weaken and shift eastward today and tonight as a
surface front approaches the region from the northwest. This will
cause the background trade wind flow to gradually diminish
through tonight. In addition, stable and dry atmospheric
conditions will limit trade shower coverage. Brief periods of
MVFR conditions are possible in passing trade showers over some
windward facing slopes and coasts. Otherwise, expect VFR
conditions to prevail.

No AIRMETs are in effect, and none are expected through this
evening.

&&

.MARINE...
Moderate to locally strong trades linger over the region, but are
expected to weaken today as a front approaches from the
northwest. The front will push the high pressure, currently
northeast of the islands, to the east. The front is expected to
reach the northwest waters near Kauai on Tuesday, and then push
down the island chain in about 18 hours. Strong northerly winds
are expected with and behind the front. High pressure is then
expected to settle in for the end of the week.

The current northwest swell is on the decline, as the nearshore
buoys have shown overnight. The High Surf Advisory (HSA) for the
Big Island has been cancelled this morning, and the High Surf
Warning (HSW) for other islands has been downgraded to an
advisory. A new, even larger swell is expected to build late today
and tonight, peaking above warning levels Tuesday night.
Anticipate the HSW for the smaller islands, and possibly a HSA for
the Big Island, to be reposted later day for this event.

With winds remaining at or near Small Craft Advisory (SCA)
levels, coupled with the current swell continuing to produce seas
in excess of 10 ft, the SCA has been extended for all waters.
Seas are expected to decrease today as the current swell continues
to subside. As mentioned above, the next swell is expected to
arrive tonight, which will bring seas once again in excess of 10
ft, which will linger into the middle of the week. As such, the
SCA has been extended for all waters through Wednesday, even
though there will be some time today and tonight over some of the
waters where conditions will briefly improve.

Surf is expected to drop below the winter time average along
north and west facing shores for the latter part of the week, and
on into the weekend.

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

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST this evening for Niihau-Kauai
Windward-Kauai Leeward-Waianae Coast-Oahu North Shore-Oahu
Koolau-Molokai-Maui Windward West-Maui Central Valley-Windward
Haleakala.

Small Craft Advisory until 6 PM HST Wednesday for all Hawaiian
waters-

&&

$$

DISCUSSION...Gibbs
AVIATION...Houston
MARINE...Ballard


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