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WindNE 30 mph
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Hawaiian Islands Synoptic Discussion and Guidance

452
FXHW60 PHFO 280632
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
832 PM HST WED JUL 27 2016

.SYNOPSIS...
Breezy trade wind weather will persist through the work week as
high pressure builds far to our north. Trades are forecast to
weaken 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...
A 1030 MB high near 40N139W, far northeast of the main Hawaiian
Islands, is driving moderate to locally strong trade winds across
local waters this evening. 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. The exception
is the Kona side of the Big Island, where daytime heating and
return flow combined to increase cloud cover there.

Afternoon soundings show sharp inversions between 4500 and 5500
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 very little shower activity. 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 north drifting west
and strengthening through the forecast period, leading to the
westward spread of locally strong trade winds as early as Thursday
afternoon and lasting into the weekend. Our current Small Craft
Advisory will likely have to be expanded with the morning forecast
package. Simultaneously, 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 northeast to east low-level trade wind flow will
continue at least through Thursday night. 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 5.5 kft to 4.5 kft, respectively.
Model guidance shows the strong inversion will likely remain in
place during the next 36 hours.

Dry and stable atmospheric conditions across the island chain will
limit most shower activity. Expect predominately VFR conditions
across most of the state. Satellite imagery shows a vast area of
broken to locally overcast stable low clouds (primarily
stratocumulus) extending from the coast of California to the
windward Hawaiian waters. The low level trade wind flow will
likely carry these low stable clouds over the windward sides of
some the islands, which may produce isolated MVFR ceilings.

&&

.MARINE...
High pressure far northeast of the state will strengthen and shift
westward, keeping trade winds breezy across the area. A small
craft advisory is currently in effect for a somewhat larger than
typical area, a sign of the stronger gradient across the islands.
The advisory may need to be expanded to additional areas on
Thursday as the high strengthens.

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 Oahu Leeward
Waters-Kaiwi Channel-Maui County Leeward Waters-Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Windward Waters-
Big Island Southeast Waters.

&&

$$

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

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