Current Conditions
Temp3.7 C
RH25 %
WindS 37 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

938
FXHW60 PHFO 012000
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
1000 AM HST FRI JUL 1 2016

.SYNOPSIS...
Strong and gusty trade winds will affect the state through
Saturday, with a slight drop pin winds expected through the rest
of the holiday weekend. A dry and stable air mass will result in
rather dry conditions with very little rainfall through Saturday.
The airmass will gradually moisten from the east through the
remainder of the holiday weekend, leading to increased showers
that will periodically spread leeward on the smaller islands.

&&

.DISCUSSION...
The main concern in the short term will be developing strong and
gusty trade winds. The trades are being driven by a relatively
strong surface high centered about 1250 miles northeast of the
islands. Wind gusts near and downwind of terrain are being
enhanced by an exceptionally low inversion being produced by a
mid level ridge building in from the east. The overnight Hilo
sounding and recent aircraft data show the inversion base below
2500 ft, and advisory level wind gusts around 50 mph are highly
likely around and downwind of areas where the inversion is near
island terrain. The window of strongest winds look to be this
evening through early Saturday. During this time, a broad and
weak mid level trough approaching from the southeast could
tighten the pressure gradient above the surface and lead to a
potential increase wind gusts. A wind advisory remains in place
through Saturday afternoon for most of the state, though there is
a small chance of experiencing high wind warning conditions on the
Haleakala summit.

Rather dry conditions will hold into Saturday. The above mentioned
mid level ridge and exceptionally low inversion will keep low
level moisture minimal. Windward terrain may squeeze out some
light showers, but dry conditions will dominate.

Trade winds will back off slightly by Sunday, and shower
activity is expected to return to more normal levels. The above
mentioned, broad, mid level trough will pass over the islands from
east to west. While the surface high to the north will change
little, the easing of the mid level pressure gradient and rising
of the inversion is expected to cause winds to decrease enough to
drop the wind advisory. The mid level trough will also bring an
increase in low level moisture that will boost shower activity
back to normal levels. Expect mainly windward rainfall, with
breezy trade winds carrying a few showers over leeward portions of
the smaller islands at times.

The high clouds that have been producing periods of interesting
sky conditions during the past several days will thin over at
least the eastern half of the state. Weak upper level ridging
will edge westward and displace the persistent upper level low
sitting about 700 miles west-northwest of Kauai over the next 24
hours or so. Thicker high clouds will likely return on Tuesday.

&&

.AVIATION...
Strong and gusty trade winds and stable atmospheric conditions
will persist across the island chain through Saturday. Therefore,
AIRMET Tango remains in effect for moderate to isolated severe low
level turbulence over and immediately leeward of the higher
terrain on all islands. In addition, we will also include
sustained surface wind speeds of 30 knots or greater.

A few low clouds may impact windward facing slopes and mountains
today resulting in brief and localized MVFR ceilings. Otherwise,
expect VFR conditions to prevail.

&&

.MARINE...
Elevated trade winds will likely hold through the holiday weekend,
with gale force winds expected over the typically windy waters
around the Big Island and Maui through Saturday. The latest
nearshore wave guidance indicates the maximum seas reaching 9 to
10 ft across most waters and 12 to 14 ft across the Alenuihaha
Channel and south of the Big Island. Trade winds will slightly
ease on Sunday, though a Small Craft Advisory will likely be in
place for all waters through at least Sunday and possibly through
the entire holiday weekend.

Rough, advisory-level surf will be possible along the east facing
shores over the weekend, beginning as early as tonight. Elsewhere,
no significant surf is anticipated through the weekend. Looking
ahead through the upcoming week, the latest WW3 and ECMWF-Wave and
ensemble wave guidance depict a good sized batch of gales setting
up just east of New Zealand today into the weekend within Hawaii's
swell window. This setup will likely translate to moderate surf
along south facing shores by the end of next week.

&&

.FIRE WEATHER...
Strong and gusty trade winds and a rather dry air mass will
remain over the islands through Saturday. Rainfall received in
late May slightly eased drought conditions across the islands,
which rules out the possibility of Red Flag Warning criteria
being met. However, fire danger will be elevated due to the
strong winds and low afternoon humidities.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 6 PM HST Saturday for all areas except Big
Island Summits.

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

Small Craft Advisory until 6 PM HST Sunday for all other waters
and channels.

&&

$$

Wroe

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