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Temp4.0 C
RH8 %
WindWSW 2 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

392
FXHW60 PHFO 240154
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
354 PM HST Thu Jan 23 2020

.SYNOPSIS...
A stable land and sea breeze pattern will continue through
tomorrow afternoon. An area of moisture moving up from the
southeast will produce moderate showers along southeast slopes of
the Big Island, while the rest of the state will experience dry
conditions tonight and afternoon clouds and minimal rainfall
Friday. A weak front will stall near Kauai Friday night, bringing
an increase in clouds and showers for the northern end of the
island chain into Saturday. Moderate trade winds and a typical
windward rainfall pattern will return for the weekend. Trades will
decrease and likely veer southeasterly again early next week.

&&

.DISCUSSION...
Stable and dry conditions persist across Oahu and Maui County this
afternoon, while pockets of shallow moisture are bringing clouds
and a few showers to the Big Island and, to a lesser extent, on
Kauai. An approaching front has pushed the subtropical ridge
southward across the central portion of the state, putting the
island chain under a stable south to southeast background flow
that has been overpowered by sea breezes this afternoon. A small
pocket of moisture passing west and north of Kauai produced a few
interior showers this afternoon and is lifting northward.
Meanwhile, a larger area of shallow moisture is moving over the
Big Island from the southeast. Clouds and a few showers have
developed along east and southeast facing slopes of the Big Island
this afternoon, and the Hilo sounding showed the inversion still
strong but lifted up to 9,300 ft. Across Oahu and Maui, dry
conditions dominate.

Dry and stable conditions will prevail from Kauai to most of Maui
tonight, while the area of moisture will continue to produce
clouds and scattered showers over the Puna and Kau Districts of
the Big Island. From Kauai to Maui, overnight land breezes will
once again produce mostly clear skies with temperatures dropping a
couple degrees below January normal.

The state will remain under a stable land and sea breeze pattern
during the day on Friday. The area of moisture will remain over
the Big Island and may make it as far west as east Maui,
providing a boost in clouds cover and modest shower activity. The
rest of the island chain will continue to experience little, if
any, rainfall.

A weakening front will drift southward and stall near Kauai
Friday night and Saturday. Kauai will likely experience an
increase in clouds and showers, while surface high pressure
building to the northwest drives increasing trade winds state-
wide. A persistent mid level ridge will maintain stable
conditions, with modest showers confined to windward slopes.

Trades will decrease and will likely become disrupted again early
next week. Another approaching front will push the subtropical
ridge southward, leading to east-southeast winds on Monday and
possibly southeasterly winds for Tuesday and Wednesday. There is
some uncertainty as to whether or not winds will veer enough to
cause light and variable winds from Kauai to Maui. However, a
ridge aloft will maintain stable conditions.

&&

.AVIATION...
For the next 24 hours, VFR conditions are expected to continue
across the island chain. Light showers may impact windward sides
of the islands this afternoon due to sea breezes, but all interior
areas will clear out overnight from land breezes. As high
pressure dominates our area, light and variable winds are
expected. Best chances for lower ceilings and rainfall will be
along the windward and southeast slopes of Big Island, which will
hang into the overnight time frame.

No AIRMETS are anticipated at this time.

&&

.MARINE...
Light and variable winds will continue through early Friday, then
shift out of the north to northeast and increase into the moderate
to fresh category late Friday as a front passes north of the area.
Fresh to locally strong easterly trades are expected for a brief
period over the weekend before trending back down by early next week
as a series of fronts pass to the north. Although seas may briefly
drop below the Small Craft Advisory (SCA) level (10 ft) Friday as
the large northwest swell subsides, advisory-level conditions
will return Friday night through the weekend due to a combination
of winds and seas.

Surf along north and west facing shores will remain up through next
week due a series of large northwest swells evolving from the
progressive pattern over the northern Pacific. The current swell
is on a steady decline and the High Surf Warning has been
downgraded to an advisory for tonight. Surf heights are expected
to drop down to borderline advisory levels by Friday morning.

The downward trend will be short-lived due to another large
northwest swell arriving Friday night into Saturday from a large
area of gale-to storm-force winds that has setup within the
300-320 directional band relative to the islands over the
northwest Pacific. Long-period forerunners should arrive Friday
night with surf likely building to warning levels on Saturday.
This swell will be on a downward trend on Sunday, but may still
hold at warning levels during the day and likely dropping to
advisory levels by Sunday night. As this swell eases into early
next week, advisory-level surf may hold through late Monday before
dropping below on Tuesday. Over the Big Island, this swell will
likely bring advisory level surf to exposed west facing shores
over the weekend. Another large northwest swell will be possible
by Wednesday as a gale develops over the far northwest Pacific
this weekend.

Surf along exposed east facing shores will remain small through the
period due to the lack of persistent trades locally and upstream
across the eastern Pacific.

Surf along south facing shores will remain small through next week.
A couple of background south swells expected over the weekend and
next Tuesday should be enough to keep things from going flat.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Friday for north and west
facing shores of Niihau, Kauai, Oahu, and Molokai, for north
facing shores of Maui, and for west facing shores of Big Island.

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

&&

$$

DISCUSSION...Wroe
AVIATION...TS
MARINE...Kino

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