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Temp1.9 C
RH78 %
WindNNE 29 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

117
FXHW60 PHFO 180700 CCA
AFDHFO

Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
900 PM HST Sun Jun 17 2018

.SYNOPSIS...
A weak ridge will remain north of the state for the next few days
as a weak cold front pushes south towards the state. High clouds
ahead of this system are already moving over the islands. This
front will produce mainly clouds as the atmospheric lift
associated with this system will remain north of the islands. Wind
directions shift from Tuesday night into Wednesday becoming east
to southeast potentially pushing the VOG plume from the Big Island
northwestward across the smaller Hawaiian Islands. Trade winds
will increase to moderate levels from Friday into the weekend
blowing out any lingering VOG over the smaller islands.

&&

.DISCUSSION...
An unusual weather pattern for this time of year has formed across
the Central Pacific basin. A weak high pressure surface ridge
will remain north of the state for the next few days producing
light trade winds with daytime sea breezes mainly along western
slopes of all islands. In the upper levels just east of the
islands a high and low center couplet sets up along 140W
longitude. A diminishing cold front will then drive south through
the ridge towards the state. The best low level convergence
associated with this boundary will stall and keep enhanced shower
activity north of the state. The main impact with this system will
be periods of increasing high and low clouds through Tuesday night.
Shower activity will be limited from isolated to scattered in a
relatively stable environment. Much of the shower activity over
the islands for the next several days will be driven by mesoscale
(smaller scale) convergence boundaries.

Light trade winds shift directions from Tuesday night into
Wednesday becoming east to southeast pushing the northern edge of
the VOG (Volcanic smOG) plume northwestward from the Big Island
across the smaller Hawaiian Islands with VOG lingering across most
of the state through Thursday. A building ridge north of the
islands will increase the trade winds to moderate levels from
Friday onward blowing out any lingering VOG over the smaller
islands.

Returning moderate trade winds on Friday will produce increasing
cloud and shower trends favoring more typical windward and
mountain areas of each island. An upper level low will also track
north of the islands helping to lift the cap on the trade wind
inversion and enhance shower coverage across the Hawaiian Islands
through the weekend with periods of showers potentially drifting
over leeward areas. The track of this low remains highly variable
this far out and enough differences remain between the American
(GFS) model and the European (ECMWF) model for only moderate
confidence in the long range precipitation forecast for now. Stay
tuned for updates.

&&

.AVIATION...
Surface ridge persisting just north of the islands should keep
trade winds light through Monday. Convection over the islands will
slowly decrease as the night falls, with land breezes developing.
Anticipate VFR conditions for much of the state through early
Monday, though the on-going volcanic emissions on the Big Island
will bring areas of MVFR VIS HZ to that island.

No AIRMETs are expected.

&&

.MARINE...
A nearly stationary surface ridge just N of Kauai will move
little through Monday, and then be weakened as a dissipating
front approaches from the N Monday night and Tuesday. The front is
expected to stall N of Kauai, develop into a trough, and then
gradually dissipate through Wednesday as it moves NW. Light to
locally moderate NE to E trade winds on Monday will likely weaken
by Tuesday, with winds potentially becoming more variable through
Wednesday as the large scale flow becomes quite weak. High
pressure will consolidate far NE of the area Thursday and Friday,
and then move W into next weekend, supporting increasing trade
winds. Winds will likely be strong enough to warrant a Small
Craft Advisory in the windier zones by Thursday.

The long-period WNW and S swells of the past couple of days will
diminish through Tuesday, with little significant swell expected
for most of the next week. Small, long-period SSW swell will
likely support small surf along S facing shores toward the end of
the week. Increasing trade winds at the end of the week will also
lead to increased short-period E swell.

&&

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

&&

$$

DISCUSSION...Bohlin
AVIATION...Hui
MARINE...Birchard

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