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RH69 %
WindN 15 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

833
FXHW60 PHFO 281340
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
340 AM HST THU JUL 28 2016

.SYNOPSIS...
Breezy trade wind weather will persist through the work week as
high pressure builds far to our north. Trades are forecast to
decrease slightly this weekend as an upper low approaches from
the east. Clouds and showers will favor windward and mauka areas,
but may become more active this weekend through early next week.

&&

.DISCUSSION...
Given the rather benign weather pattern, there is little or no
change in forecast philosophy from last evening. A 1030 MB high
near 40N140W, far northeast of the main Hawaiian Islands, is
driving moderate to locally strong trade winds across local waters
this morning. Satellite loop shows a broad field of stable
stratocumulus clouds extending east from the islands all the way
to the mainland. These clouds, embedded in the trades, cover
windward waters and are piling up along windward slopes, leaving
most leeward areas with clear skies so far. While daytime heating
and return flow combined to increase cloud cover across Kona
slopes on the Big Island yesterday afternoon and evening, this has
decreased dramatically overnight and this morning.

Overnight soundings show sharp inversions between 5500 and 6500
feet, with near-seasonal PWs around 1.3 inches and only neutral to
very mild instability. The inversion, associated with weak mid
level ridging, is quite effective at capping any convection, with
radar showing only light showers just east of Kauai. Cloud tops
are uniformly warm even far upwind from the islands. We expect the
current weather pattern will hold into the weekend, with clouds
and showers favoring windward and mauka areas and light total
rainfall.

Models show the governing surface high to our northeast drifting
west and strengthening through the forecast period, leading to the
westward spread of locally strong trade winds as early as this
afternoon and lasting into the weekend. The Small Craft Advisory
has been expanded to include all Hawaiian waters with this
morning's package. An upper low east of the islands is expected to
drift west, arriving in the vicinity of the islands late this
weekend into early next week. With an increase in low level
moisture from dissipated tropical depression Georgette also
depicted around this time, we expect a more active trade shower
pattern will develop from Saturday onward. Clouds and showers will
still favor windward and mauka areas, but leeward areas will see
more showers than they do now.

&&

.AVIATION...
The breezy northeasterly to easterly low-level trade wind flow
will continue at least through early Friday morning. As a result,
AIRMET TANGO remains in effect for tempo moderate low level
turbulence over and immediately leeward of the higher terrain on
all islands. The most recent soundings from PHTO and PHLI depicted
a strong trade wind inversion sloping from near 6.5 kft to 5.5
kft, respectively. This strong inversion will likely remain in
place during the next 24 hours.

Dry and stable atmospheric conditions will also continue across
the island chain, with VFR conditions prevailing over most of the
state. Satellite imagery shows a vast area of broken to locally
overcast stable low clouds (primarily stratus / stratocumulus)
extending from the coast of California to the windward Hawaiian
coastal waters. The low level trade wind flow will likely carry
these low stable clouds mainly over the windward sides of some the
islands, which may produce isolated MVFR ceilings. There is also
the possibility of a few brief windward showers that may cause
localized reductions to visibilities early this morning, primarily
near the windward Big Island.

&&

.MARINE...
High pressure far northeast of the state will strengthen and shift
westward, keeping trade winds breezy across the area. The Small
Craft Advisory has been expanded and is now in effect for all
Hawaiian waters through Friday afternoon.

Breezy trade winds will result in choppy, short-period surf along
east facing shores, but surf heights are expected to remain below
advisory levels. There will also be a series of small southerly
swells through the weekend and into next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Friday for all Hawaiian
waters-

&&

$$

DISCUSSION/MARINE...Powell
AVIATION...Houston

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