Current Conditions
Temp2.4 C
RH99 %
WindNNE 29 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

672
FXHW60 PHFO 181331
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
331 AM HST Mon Jun 18 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. Much of the shower activity over the islands for the
next several days will be driven by mesoscale (smaller scale)
convergence boundaries.

For Today, high cirrus clouds are drifting over the state from
the north. Light trade winds and daytime sea breezes along western
slopes of all islands will build low clouds and isolated to
scattered showers along windward, mountain and interior sections
of each island. Shower activity will be limited by a low trade
wind inversion heights around 5,000 feet in a relatively stable
atmosphere.

On Tuesday and Wednesday, a diminishing cold front will drive
south through the ridge towards the state. The best low level
convergence associated with this boundary will stall to the north
keeping enhanced shower activity north of the islands. The main
impact with this system will be periods of clouds through
Wednesday. Shower activity will be limited from isolated to
scattered in a relatively stable environment. Light trade winds
shift also 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 today, with early morning land breezes giving
ways to afternoon sea breezes. Anticipate VFR conditions for much
of the state today, 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 surface ridge just N of Kauai will move little today, and then
drift S and weaken as a dissipating front approaches from the N
tonight 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 today 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 on
Thursday or Friday.

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 upcoming week. Small, long-period SSW swells will
likely support tiny to small surf along S facing shores, while
locally strong trade winds at the end of the week will 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