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Temp0.8 C
RH78 %
WindSW 18 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

179
FXHW60 PHFO 080132
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
332 PM HST Wed Dec 7 2016

.SYNOPSIS...
Light winds can be expected over the next several days with daytime
sea breezes and nighttime land breezes dominating. The weather pattern
will become a bit more unsettled over the next few days due to a trough
of low pressure west of the area. Shower activity is expected to increase
later tonight and continue off and on through the weekend. A frontal
boundary is then forecast to reach the islands later this weekend and
stall out across the central islands.

&&

.DISCUSSION...
There are several weather features that will control our islands
weather over the next several days. First, a broad upper level
trough is centered several hundred miles west and northwest of the
state. A surface low along with a developing frontal boundary are
associated with this upper trough. The sets the islands up for a
rather unsettled weather pattern for the next several days.

Radar imagery is currently showing just a few showers over and
around the Aloha State this afternoon. However satellite imagery
shows increasing high cloudiness moving in from the southwest.
Presently most of these clouds are thin, but they are expected to
gradually thicken up tonight and Thursday.

Over the next few days, a series of shortwave troughs will pass
across the area. This combined with abundant low level moisture
should allow for an increase in shower activity. The moisture may
be deep enough to allow for some wintery weather over The Big
Island summits, thus a Winter Weather Advisory is posted beginning
this evening.

As these shortwaves pass across the area, shower chances will
likely increase but timing and location remains problematic as
low level forcing remains weak. There is also a slight chance for
thunderstorms over the west end of the state on Thursday as the
first short wave passes by. Thus unsettled weather can be
expected at times through Saturday but rainfall will not occur all
the time and over all locations.

By Sunday models indicate the upper trough will be moving eastward
with a surface frontal boundary moving over the state. An
increase in showers will likely accompany the front. Light
northeast winds are forecast to fill in behind the front. However
models indicate that the frontal boundary will likely stall in the
island vicinity. Thus wherever the front stalls along with the
northeast low level wind flow, showers will likely continue to
fall but become more windward and mauka oriented.

&&

.AVIATION...
Clouds have filled in across interior portions of the islands.
Ceilings are generally VFR with occasional MVFR conditions in
showers. With generally light east-southeast low-level flow,
afternoon showers are favoring northwest sections of the islands
where convergence along sea breezes is maximized. A band of
moisture associated with the surface trough near the Big Island
will lead to more widespread MVFR conditions across windward and
southeast sections. An AIRMET is in effect due to persistent
lower ceilings. Brief IFR conditions in heavier showers are also
possible before conditions start to improve later in the evening.
Another cloud band may develop over the western half of the state
late tonight/early Thursday, with the potential for more
widespread MVFR ceilings and embedded heavier showers.

A southwesterly upper level jet will bring increasingly thick
mid/high level clouds. There have been a few reports of moderate
high-level turbulence north of the state associated with this jet.
We are starting to see an increase in transverse bands near the
islands, and have issued an AIRMET for high level turbulence.
There may be a threat of icing overnight as the mid-level clouds
thicken, and this will bear watching for AIRMET potential as well.

&&

.MARINE...
Mainly gentle winds will prevail through at least the weekend. A
weak, nearly stationary surface ridge is located roughly 175 nm
north of Kauai, and a weak surface trough stretching over the Big
Island is creeping westward. The trough will dissipate, and the
ridge will shift over the islands on Thursday, causing the weak
easterly winds to veer out of the southeast and south. Northerly
winds are expected to develop over the western portion of the
island chain on Sunday and Monday as the tail end of a weak trough
or front moves over the islands.

A northwest swell around 4 to 5 feet at 15 seconds will peak
through the night, producing surf well below advisory levels
along north and west facing shores. A smaller north swell around 3
feet at 11 seconds is also present. These swells will decline on
Thursday, leaving very small surf to prevail across all shores on
Friday through the weekend. A moderate north swell is possible
early next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 6 PM this evening to 6 AM HST
Friday for Big Island Summits.

&&

$$

Synopsis/Discussion...Burke
Aviation...Bravender
Marine...Wroe

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