Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 142005
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
1005 AM HST Thu Dec 14 2017

.SYNOPSIS...
Cool and windy conditions will remain into Friday before winds
decrease and the chance of rain increases. An upper level trough
will bring unsettled weather to portions of the state Friday and
through the weekend. Partly cloudy skies with scattered showers
are expected over the weekend with pockets of heavy rain.

&&

.DISCUSSION...
High pressure north of the state is providing dry air and gusty
north to northeast winds. A wind advisory is in effect for most
areas through today and may be extended into tonight. Some quick
hitting showers are moving through windward and north facing areas
with limited rainfall totals. Dew points remain below normal making
temperatures feel cooler. This windy and mainly dry weather
regime will remain through tonight before transitioning to a
wetter pattern Friday and over the weekend. The gusty trade winds
will continue into Friday before weakening from east to west
across the state starting Friday night as a surface trough moves
in from the east.

A high wind warning is in effect for the Big Island summits
today with an approaching upper low accelerating winds at the
summit level.

Inclement weather will be possible starting Friday as the upper
low drops from the higher latitudes and reaches a position
northeast of the islands Friday. The upper low will bring
instability and cold temperatures to the middle and upper
atmosphere allowing for increasing, and heavier showers. The
instability aloft, the trough at the surface, and increasing low
level moisture will lead to the possibility of heavy rain and
isolated thunderstorms, and the chance of snow for the Big Island
summits. The current forecast favors the eastern half of the state
for the heavier rain with the chance of afternoon thunderstorms
Friday and Saturday with daytime heating and sea breezes expected
to tap into the instability aloft.

The upper low is expected to maintain a position just NE of the
islands on Saturday, and then slowly pull away to the NE on
Sunday. The low will maintain at least slight instability through
the weekend, with the threat of heavy rain remaining. Saturday
looks to be a convective day with light winds and clear skies in
the morning, switching to sea breezes with clouds, showers, and
isolated thunderstorms in the afternoon. By Sunday, the surface
trough is forecast to be located west of the state, bringing
southerly winds across the area with scattered showers with some
embedded downpours. Widespread showers are becoming a distinct
possibility Monday and Tuesday with another upper level trough
dropping over the islands from the northwest, and deep tropical
moisture pushing up from the southeast.

&&

.AVIATION...
A strong and gusty north-northeast flow will persist into Friday
as a cutoff low aloft develops just northeast of the state. The
low level flow is rather stable over the western end of the island
chain, with some enhanced low level moisture affecting the eastern
half of the state today. Widespread, moderate low level turbulence
will occur over and downwind of island terrain today, while an
isolated instance of severe low level turbulence possible. AIRMET
Tango for moderate low level turbulence remains in effect for all
islands today and will be extended into Friday. A northerly jet
stream aloft will produce moderate turbulence at upper level
today.

Expect VFR conditions to prevail over most areas, though MVFR
ceilings will occur over northeast slopes the Big Island and Maui
County.

&&

.MARINE...
A High Surf Warning remains in effect for north and west facing
shores of most islands with a High Surf Advisory (HSA) for north
facing shores of the Big Island through this evening. The current
northwest swell has peaked, but will still be quite large today,
before slowly subsiding through Saturday. Strengthening winds will
cause rough surf on east facing shores tonight into the weekend.
This surf may get big enough to require a HSA for east facing
shores.

A Small Craft Advisory (SCA) is in effect for most waters for
strong north winds, as well as large seas due to the northwest
swell, with a Gale Warning in effect for the Alenuihaha Channel.
Northeast winds will peak today as the pressure gradient between a
high to the north and a trough to the east tightens. Winds will
subside tomorrow into Saturday as the trough approaches from the
east.

The approaching trough will bring increasing moisture and
instability, so thunderstorms are possible as early as this
evening over the windward waters of Maui and the Big Island, with
the chance lingering through Saturday.

See the Collaborative Surf Discussion for details on surf and
swell.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 6 PM HST this evening for Niihau-Kauai-Oahu-
Molokai-Lanai-Kahoolawe-Maui Windward West-Maui Leeward West-
Maui Central Valley-Windward Haleakala-Leeward Haleakala-Kona-
South Big Island-Big Island North and East-Kohala-Big Island
Interior.

High Surf Warning until 6 PM HST this evening for Niihau-Kauai
Windward-Kauai Leeward-Waianae Coast-Oahu North Shore-Oahu
Koolau-Molokai-Maui Windward West-Maui Central Valley-Windward
Haleakala.

High Surf Advisory until 6 PM HST this evening for Big Island
North and East.

High Wind Warning until 6 PM HST this evening for Big Island
Summits.

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-Maui County Leeward Waters-Maalaea Bay-
Pailolo Channel-Big Island Windward Waters-Big Island Leeward
Waters-Big Island Southeast Waters.

Gale Warning until 6 PM HST this evening for Alenuihaha Channel.

&&

$$

Morrison...Discussion
TS...Marine
Wroe...Aviation



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