High Surf Advisory 55, NWS Honolulu, HI

Area Forecast Discussion...UPDATED
National Weather Service Honolulu HI
1121 AM HST Tue Dec 13 2016

.UPDATE...
Extended High Wind Warning for Big Island Summits until Midnight
tonight due to continued strong winds reported by surface
observations.

&&

.SYNOPSIS...
Mainly fair weather is expected for the islands through Wednesday as
a drier and stable air mass will stay in the area. More wet and
unsettled weather is expected to return for the later half of the
week and this weekend as a front and its associated low pressure
system will likely reach the state.

&&

.DISCUSSION...
Upper level ridging will build over the state from the west resulting
in a stable airmass over the islands today. Early morning
soundings show a low precipitable water (PW) value of 0.92 inches
at Lihue with a strengthening inversion around 7500 feet. The Hilo
sounding showed a wetter and more unstable profile, but is
trending drier and more unstable as the ridge builds east.

At the surface, gentle northerly winds are driven by a high far
north of the state. The north winds are blowing in relatively cool
and dry air and most of the state is sunny or partly cloudy. Last
night's dew points dropped into the upper 50s across Kauai and
lower 60s across Oahu. Showers are expected to be limited today
with the highest chance near the Big Island where most of the
moisture is concentrated.

Big Island summit winds remain at the warning levels this morning
with the expected down trend today. If current wind speeds
continue into this afternoon, the High Wind Warning may need to be
extended.

Winds are expected to turn more easterly by Wednesday as a weak
surface ridge established north northeast of the area. Conditions
are expected to remain dry and stable.

Active weather is once gain expected to return to the islands
beginning Thursday, models indicate another front will approach
the islands from the northwest, advancing eastward across the
state through Friday night. The front will bring a band of clouds
and showers over the state as it passes through. The parent
surface and upper lows will drop south and approach the western
end of the state this weekend, then move west and weaken early
next week.

As the upper low approaches the islands, the initial surge of
colder air aloft makes its way over the area on Friday. 500 mb
temperatures will fall to around -13 to -15 celsius, approximately
the coldest 3-5 percent of days based on sounding climatology.
These cold temperatures aloft will remain below -10 celsius
through at least Monday. Instability will be enough to trigger
thunderstorms, however, moisture will initially be limited on
Friday (and potentially Saturday as well) until the surface low
finally nears the islands Saturday night. The sensible weather
details are tough to pin down 3 to 5 days out. We will likely see
some adjustment in the forecast in the coming days and the
introduction for a chance for thunderstorms.

&&

.AVIATION...
There are no AIRMETs in effect and none are expected through this
evening. A weak band of showery low clouds spinning off a low NE of
the area may bring enough low ceilings to windward areas tomorrow
morning to require AIRMET SIERRA for MTN OBSC.

VFR will prevail at the TAF sites over the main Hawaiian islands,
but TEMPO MVFR is possible over N sections as N winds carry patches
of showery low clouds over the islands.

&&

.MARINE...
A north northeast swell is expected to arrive later today. This
swell may be high enough to bring a potential for a high surf
advisory for the east facing shores with a northern exposure late
tonight or Wednesday morning. The peak of this swell will also
coincide with the full moon high tides, during the early morning
hours with a predicted height of 2.6 feet Wednesday and Thursday.
Readings from tide gauges around the state have been running
higher than predicted levels, so these tides could be a bit higher
than predicted levels. A new northwest swell is forecast to arrive
Thursday night and build to near advisory levels Friday along
north and west facing shores. The potential for a gale low north
of the islands later this week may complicate the swell and surf
outlook. If the southerly winds develop as forecast, the surf
along south facing shores may also see a slight rise with choppier
waters.

Both winds and seas are expected to stay below small craft advisory
criteria through the week, though the combined seas heights will be
near the criteria level due to the pending northerly swells for the
exposed coastal waters.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until Midnight HST today for Big Island
Summits.

&&

UPDATE/DISCUSSION/MARINE...Foster
AVIATION...Donaldson