Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 130159
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
359 PM HST Tue Dec 12 2017

.SYNOPSIS...
A cold front will move down the island chain bringing clouds and
showers through Wednesday. Breezy north winds with cool and dry
conditions will fill in behind the front tonight through Thursday,
with unsettled weather on the horizon Friday and into the
weekend.

&&

.DISCUSSION...

A weakening cold front near Oahu will continue moving east into
Maui County this evening bringing clouds and showers. The front
will continue into the Big Island Wednesday morning. Rainfall
with this front will be light to moderate with some isolated
pockets of higher totals where the terrain induces some heavier
rains. High pressure pushing in from the northwest behind the
front will usher in gusty north to northeast winds and clearing
skies. Dew points will drop into the 50`s behind the front making
temperature feel cooler than normal through Thursday. The dry air
will also put a cap on most showers keeping any rainfall totals
low.

Changes in the weather are afoot late in the week as global
models are consistently depicting an upper level low dropping
south as it cuts off from the jet stream to the north, reaching a
position northeast of the islands Friday. The upper low will
bring instability and cold temperature to the middle and upper
atmosphere allowing for increasing, and heavier showers. Near the
surface, a low is expected to form east of the state in response
to the upper low. The instability aloft, low pressure near the
surface, and increasing low level moisture will lead to unsettled
weather over the islands with the possibility of heavy rain and
thunderstorms, and the chance of snow for the Big Island summits.
However, models are still having a difficult time agreeing with
the location of the upper low and the timing of how long the low
stays in the island`s vicinity. The current forecast has
increasing showers and rainfall totals Thursday night through
Saturday. We will likely introduce a slight chance of
thunderstorms to the forecast starting Friday over the eastern
windward waters as the upper low will mostly likely bring
instability over those areas. More fine tuning will continue as
the details become clearer as model solutions converge.

&&

.AVIATION...
A weakening cold front over east Oahu will track eastward to Maui
County this evening, and the Big Island overnight/early Wednesday
morning. There will be widespread MVFR with isolated IFR
ceilings/visibility within showers along the frontal band. The
front will weaken with areas of MVFR once it reaches Maui and the
Big Island. AIRMET Sierra is currently posted for mountain
obscurations on Oahu, Molokai and Lanai. AIRMET Sierra will
likely go into effect for Maui for mountain obscurations this
evening as the front approaches.

&&

.MARINE...
The incoming north-northwest swell was a little slow to arrive at
Buoy 51101, but has since caught up. Although the swell may be
subsequently slow to rise at the local buoys, it appears to be
back on track to peak tonight into Wednesday. It is expected to be
larger than the last swell, and will produce warning-level surf
on north and west facing shores of the smaller islands. Surf on
the north facing shores of the Big Island is expected to reach
advisory levels in some areas, but with a lot of local variations
due to the expected 320-330 degree direction of this swell.
PacIOOS run-up forecasts for the Oahu north shore indicate
possible overwash of some lower roadways near the coast during the
peak of this event. A High Surf Warning is in effect for most
north and west facing shores of the smaller islands through
Thursday. A High Surf Advisory has also been issued for the north
facing shores of the Big Island for tonight through Thursday.

This new swell will also bring seas above 10 feet across most of
the marine area, spreading across the area through Wednesday
morning. A Small Craft Advisory (SCA) has been posted for most of
the local marine area. Seas are forecast to remain above 10 feet
for most waters through Friday.

A cold front is forecast to move down the island chain through
Wednesday morning, with northerly winds increasing behind the
front. Winds behind this front will likely reach SCA levels across
much of the area by Wednesday afternoon or evening. These strong
winds are expected to continue on Thursday, then decrease from
east to west across the area Friday into Saturday.

See the latest Oahu Surf Discussion (SRDHFO) for additional details
on surf and swell.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Warning until 6 PM HST Thursday 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 Thursday for Big Island North
and East.

Small Craft Advisory until 6 AM HST Friday for Maui County
Leeward Waters-Pailolo Channel-Alenuihaha Channel-Big Island
Windward Waters.

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.

&&

$$

Morrison...Discussion
TS...Marine
Foster...Aviation


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