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RH11 %
WindNNE 20 mph
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Hawaiian Islands Synoptic Discussion and Guidance

343
FXHW60 PHFO 080654
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
854 PM HST Sat Dec 7 2019

.SYNOPSIS...
Light and variable winds will continue through the first half of the
upcoming week as a front moves into the area and stalls to the
north. Outside of a few clouds and showers setting up over interior
areas each afternoon due to sea breezes, mostly dry and stable
conditions are anticipated. Increasing moisture associated with
another front that is forecast to move down the island chain will
bring increasing rainfall chances and gusty trades by the end of
the week.

&&

.DISCUSSION...
Water vapor imagery showed very dry conditions aloft due to a ridge
extending eastward across the islands. Satellite data and the
afternoon upper air soundings at Lihue and Hilo reflect these dry
conditions with precipitable water (PW) measurements just over an
inch. The latest surface analysis showed a ridge extending
southwestward to an area near the western end of the state and a
cold front located a few hundred miles northwest of Kauai. Outside
of a few light showers near the southeast coast of the Big Island
this evening, mostly clear and dry conditions are in place. Expect
this trend to hold overnight into Sunday, especially as the land
breezes setup.

The latest short-term (through Tuesday) guidance remains in decent
agreement and depicts mostly dry and stable conditions prevailing as
the aforementioned front stalls and diminishes just north of the
area and the ridge sets up over the islands. Light and variable
winds will translate to a land and sea breeze regime. Although dry
conditions will prevail, a few clouds and showers setting up over
interior areas can't be ruled out each afternoon due to the sea
breezes.

For the extended period (Wednesday through next weekend), guidance
depicts lowering upper heights associated with a strong short wave
trough approaching and moving into the area Wednesday through
Friday. Although it remains too early to determine any specifics,
increasing moisture and rainfall chances along with gusty trades
remain a possibility by or come Friday as the attendant cold front
moves down the island chain. Breezy trades along with a drying
trend will be possible next weekend as high pressure builds north
of the state in the wake of the front.

&&

.AVIATION...
Winds continue to be light with sea breezes in the afternoons and
land breezes at night. That pattern looks as if it will continue
through Sunday night. There is not a lot of moisture across the
state. There may be a few showers along the windward slopes. Other
than those showers, possibly causing brief MVFR conditions, the
rest of the state should see VFR conditions.

There are no AIRMETs currently in effect or expected.

&&

.MARINE...
A ridge of high pressure just north of the state will shift
southward and over the island chain tonight through Sunday night
as a front approaches from the northwest. This will keep a light
and variable wind regime in place across the marine area. The
front will stall out north of Kauai Monday through Wednesday, with
the ridge axis shifting back north of the islands, bringing a
return of light to locally moderate trades. A front is expected to
approach from the northwest late in the work week, and depending
on how far south this front progresses, could bring strong,
possibly near Gale force winds to marine area Thursday night
into next weekend.

A north-northeast swell is bringing 10 feet seas to portions of
the marine area. Therefore, a Small Craft Advisory (SCA) remains
in effect through tonight for waters exposed to this swell. This
swell may also produce harbor surges at both Kahului and Hilo
harbors.

The current north-northeast swell is producing warning level surf
along exposed east facing shores and advisory level surf along
exposed north facing shores. This swell will trend downward later
tonight and Sunday, and the warning will likely be transitioned to
an advisory for east facing shores, while north facing shores may
drop below advisory thresholds, but will monitor this through the
night and make a decision with the morning forecast package. The
swell will continue to gradually lower Sunday night and Monday,
likely dropping below advisory thresholds along all shores by
Monday morning.

A new northwest swell is expected to arrive Sunday, then
gradually build Sunday night and Monday. Advisory level surf will
likely impact exposed north and west facing shores late Monday
through mid week, before a much larger northwest swell arrives.
This larger northwest swell is expected to arrive Wednesday,
likely pushing surf to warning levels along north and west facing
shores beginning during the day Wednesday and holding at warning
levels through Thursday and possibly into Friday.

No other significant swells are expected.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Warning until 6 AM HST Sunday for Kauai Windward-Oahu
Koolau-Olomana-Molokai Windward-Maui Windward West-Windward
Haleakala-Big Island North and East.

High Surf Advisory until 6 AM HST Sunday for Niihau-Oahu North
Shore-Molokai Leeward-Maui Central Valley.

Small Craft Advisory until 6 AM HST Sunday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Channel-Oahu Windward Waters-
Kaiwi Channel-Maui County Windward Waters-Alenuihaha Channel-Big
Island Windward Waters-Big Island Southeast Waters.

&&

$$

DISCUSSION...Gibbs
AVIATION...Chevalier
MARINE...Jelsema

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