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Hawaiian Islands Synoptic Discussion and Guidance

194
FXHW60 PHFO 081341
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
341 AM HST Sun Dec 8 2019

.SYNOPSIS...
Light winds will continue through the first half of the 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
early morning 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 over the adjacent waters, mostly clear and
dry conditions are in place. Expect this trend to hold through the
early morning hours today with only a few showers possible over
interior areas this afternoon.

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 continuing.
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, especially over Kauai near the stalled
front.

For the extended period (Wednesday through next weekend), guidance
depicts lowering upper heights associated with a strong short wave
trough approaching and moving over the region 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 into the area. 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. This weather pattern will continue into
Monday. There is not a lot of moisture across the state. There
may be a few showers along the windward slopes. Other than those
very isolated showers, which may cause 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 will remain over the island chain
today and tonight 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 this morning, with seas expected to subside as the
day progresses. Therefore, a Small Craft Advisory (SCA) remains
in effect for waters exposed to this swell through Noon today.
This swell may also produce harbor surges at both the Kahului and
Hilo harbors.

The current north-northeast swell has been slow to lower so far
this morning, but is expected to trend downward later today. As a
result, the High Surf Warning (HSW) for east facing shores and
High Surf Advisory (HSA) for north facing shores has been
extended through Noon today. The HSW will likely be transitioned
to an advisory for east facing shores later today, while north
facing shores will likely see surf drop below HSA thresholds. The
swell will continue to lower tonight and Monday, likely dropping
below advisory thresholds along all shores by Monday morning.

A new northwest swell is expected to arrive later today, then
gradually build tonight 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. This swell is
expected to lower Friday and Friday night, with yet another large,
possibly advisory level, northwest swell arriving over the
weekend. No other significant swells are expected.

No other significant swells are expected.

&&

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

High Surf Advisory until noon HST today for Niihau-Oahu North
Shore-Molokai Leeward-Maui Central Valley.

Small Craft Advisory until noon HST today 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