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Temp9.9 C
RH10 %
WindNW 13 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

923
FXHW60 PHFO 302001
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
1000 AM HST SAT JUL 30 2016

.SYNOPSIS...
Light to moderate trade winds will become a little stronger by the
middle of next week, with trade winds potentially diminishing again
next weekend. The trades will carry areas of moisture over the
islands through the period, with clouds and showers most prevalent
over windward slopes and coasts. A nearby low aloft will keep
showers somewhat active the next couple of days, with a few showers
becoming briefly heavy. Although the low will move away from the
islands by the middle of the week, enhanced moisture from the
remnants of dissipated Hurricane Frank may fuel additional showers
Thursday and Friday.

&&

.DISCUSSION...
A relatively strong 1033 mb high pressure cell will prevail far NE
of the islands the next couple of days before shifting W and
strengthening to near 1038 mb during the middle and second half of
next week. A low aloft now centered about 650 miles NE of the
islands will keep winds over the islands lighter than one might
expect with a high of this strength to the NE, as it reducing the
local pressure gradient. It is also weakening the subsidence
inversion, with overnight soundings indicating a weakened inversion
based at a higher-than-normal 10 kft. Radar returns shows that a
few of the trade wind showers have small cores near 50 dBZ,
indicating pockets of briefly heavy showers, especially over Kauai
and Oahu this morning.

The slow-moving low aloft is expected to weaken and move
sufficiently far from the islands around Tuesday and Wednesday to
allow the low-level gradient to tighten, and trade wind speeds to
increase. While the departure of the low would typically lead us to
expect a trend toward a drier trade wind weather pattern, especially
with a mid-level ridge developing overhead, global models are
indicating that moisture associated with the remnants of now-
dissipated Hurricane Frank may arrive on the trade wind flow
Thursday and Friday, leading to increased showers. Another
potential moisture source could become embedded in the trade wind
flow to fuel more showers next weekend, but confidence is low with
respect to that portion of the forecast.

&&

.AVIATION...
A somewhat moist trade wind flow will produce periods of MVFR
ceilings and VIS in shra along windward slopes through tonight.
VFR will prevail over leeward areas, except for MVFR ceilings over
leeward Big Island slopes in the afternoon. Moisture will be more
plentiful near Kauai through the morning, but we do not expect
extensive mountain obscuration. Radar VAD wind profiles show that
trade winds are mainly 20 kt or less in the low levels of the
atmosphere, but conditions near Kauai will be border line for low
level turbulence today.

&&

.MARINE...
Winds and seas are expected to remain below small-craft-advisory
(SCA) levels for the next few days as a low aloft weakens the
pressure gradient over the area. As the low moves N around the
middle of next week, the pressure gradient will tighten and trade
wind speeds will increase. Winds may become sufficiently strong at
that time to support the issuance of a SCA for the windier marine
zones around Maui and the Big Island.

There will be a series of small long-period S swells through the
next week, but surf will remain below advisory levels. Trade winds
will drive short-period wind waves toward the islands from the E,
producing moderate below-advisory surf along E facing shores.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION/MARINE...Birchard
AVIATION...Wroe

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