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Hawaiian Islands Synoptic Discussion and Guidance

025
FXHW60 PHFO 220633 CCA
AFDHFO

Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
833 PM HST Sat Jan 21 2017

.SYNOPSIS...
A front moving southeastward across the state will stall near the
Big Island tonight. High pressure moving in behind the front will
bring strong, gusty and potentially damaging winds tonight, which
will gradually taper off Sunday and Monday. Moderate trade wind
weather will perist through the rest of the week.

&&

.DISCUSSION...
Infrared satellite shows a cold front over Maui County this
evening that will move southeast and stall near the Big Island
later tonight. A strong surface high moving in behind the front
will drive strong, gusty, and potentially locally damaging
northeast trade winds across the islands and local waters tonight.
Radar shows showers associated with the front mainly moving across
Maui and the Big Island this evening with most of the showers
focused over windward and mauka areas. Some showers are spreading
onto leeward sides of these islands. On Kauai and Oahu, showers
have tapered off since this afternoon.

Surface observations around the state currently report sustained
winds in the 20 to 40 mph range with gusts to 60 mph in exposed
areas and downwind of the mountain ranges. A High Wind Warning
remains in effect for the entire state (except for Big Island
summits and Haleakala summit) through tonight. There is the
possibility for a Wind Advisory or an extension of the High Wind
Warning for all or portions of the state into the day Sunday. We
will be considering our options for Sunday's wind highlights
later tonight.

An upper level trough with an axis about 450 miles west of Kauai
this evening will track east over the area on Sunday and Sunday
night. This will likely push high clouds over the state beginning
tonight for Kauai, then spreading eastward. The passing of the
upper trough will raise the inversions and allow for the trade
winds to weaken somewhat. Along with this, the high pressure
system behind the front driving the strong trades will quickly
move east and begin track away from us beginning Sunday.

For Sunday and Sunday night, expect trade winds to remain strong,
however, weaker than they are currently. The front will stall near
the Big Island and the trades will funnel showers onto windward
and southeast portions of the islands. Drier air will fill in over
the smaller islands, but low stratocumulus clouds and the earlier
mentioned high clouds will likely keep the broken to overcast skies.

Trade winds will continue dropping on Monday as the high (now
to the northeast) weakens as a front passes north of our area. Winds
may even see a brief shift out of the east southeast around Monday
night as the front passes. Models hint that some of the dissipated
frontal moisture will drift back up over windward portions of the
state during this period, but should be short lived. Showers over
windward Big Island will likely linger through Monday night.

From Tuesday to the end of the week, a broad high pressure system
will set up far to our northeast with a ridge passing north of
Hawaii. This setup with drive generally moderate trade winds with
occasional windward and mauka showers moving through. The
atmosphere should remain stable through this period.

&&

.AVIATION...
A wind packed front with scattered showers at 8 pm HST lies
across Maui County. It will continue to move south reaching the
Big Island later tonight, and will likely take the entire day
tomorrow for the front to move across the island.

Widespread MVFR isolated IFR conditions are currently affecting
primarily the windward sections of Molokai Maui and Lanai but
there are isolated pockets of these conditions present over on
the lee side. Expect a slow but gradual improving trend through
midnight. So, AIRMET Sierra could be lifted as the

Showers activity scattered along the Hamakua coast of the Big
Island down to the Puna district and the approaching front will
keep AIRMET SIERRA in place well into Sunday. AIRMET SIERRA for
Kauai Oahu will be lifted as clouds and showers have eased up
there.

Regarding the SIGMET OSCAR for low level turbulence for the
smaller islands, reports have been light to moderate. Based on
this assessment, will let the SIGMET expire at 0725 UTC. AIRMET
TANGO for low level turbulence will then fill in. TANGO is already
covering the Big Island.

An high level AIRMET over the islands between FL280 and FL320,
will be reassessed. There is the possibility it will be lowered.

&&

.MARINE...
Evening surface observations show very strong northeast trade
winds across the state, and a Gale Warning will continue overnight
for all Hawaiian coastal waters. The Gale Warning will continue
through Sunday afternoon for the windy areas around Maui County
and the Big Island. Advisory-level winds and seas will very
likely continue across all other waters on Sunday when the winds
diminish below gale force.

Very strong trade winds and a short-period north swell will
combine to produce surf above the advisory level on east facing
shores of all islands. A High Surf Advisory remains in effect for
those areas through Sunday afternoon. This advisory may need to
be extended. A new large northwest swell will likely produce surf
well above the advisory threshold along north and west facing
shores of the smaller islands from Tuesday through Thursday
morning. Another large northwest swell may produce advisory-
level surf along north and west facing shores of the smaller
islands starting Friday night and continuing into next weekend.
Otherwise, a small bump in surf in south facing shores is possible
on Sunday due to a small but long period south swell.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 6 AM HST Sunday for for all portions of
the state except for Big Island summits and Haleakala summit.

High Surf Advisory until 6 PM HST Sunday for all east facing
shores except for Kahoolawe.

Gale Warning until 6 PM HST Sunday for Maalaea Bay-Pailolo
Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island
Southeast Waters.

Gale Warning until 6 AM HST Sunday for all remaining coastal
waters.

&&

$$

DISCUSSION...Foster
AVIATION...Lau
MARINE...Jacobson

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



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