Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 041946
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
946 AM HST Sun Dec 4 2016

.SYNOPSIS...
An unsettled weather pattern will continue across the state today,
as an upper level trough and deep tropical moisture move over the
area. Active weather may linger over central and eastern parts of
the state tonight into Monday, but somewhat drier conditions
should return to western sections. Another round of wet weather
with locally heavy rains will be possible around midweek. Winds
will be rather light for the most part favoring daytime sea
breezes and nighttime land breezes.

&&

.DISCUSSION...
Abundant layered cloudiness is streaming over the entire state.
Radar shows numerous showers with embedded thunderstorms concentrated
over the Kauai Channel with rain getting set to move onto Kauai
soon. Stratiform rain is also moving onto the Big Island from the
southwest. Expect the cloud cover to continue with increasing
showers over the islands through the rest of today. A Flash Flood
Watch is in effect statewide today for potential flooding from
heavy rain and thunderstorms.

Surface analysis depicts a surface trough just west of Kauai,
with a north-lifting low about 400 miles north of the state. Weak
low-level wind flow prevails over the islands due to these features.
Aloft, water vapor imagery shows a deep/sharp longwave trough axis
about 150 miles west of Kauai this morning and moving slowly
eastward. The 12Z Lihue sounding shows a fairly moist and unstable
profile, with no inversion and PW value of 1.40 inches, while the
12Z Hilo sounding has temporarily dried out and stabilized with PW
down to 1.12 inches. MIMIC-TPW imagery shows a moist plume
extending from the deep tropics east of the upper trough axis, with
higher PW values moving over the state from the southwest. MIMIC-
TPW shows a dry pocket evident over and northeast of the Big
Island, which likely accounts for the drier 12Z Hilo sounding.

The upper level and surface troughs are forecast to move slowly
eastward across the state through tonight. Models show a surge of
deep moisture and synoptic-scale lift moving northward over the
islands today and tonight. A mid-level dry slot edges eastward
into Kauai by late this evening, then over Oahu by early Monday
morning, but deep moisture remains over Maui and the Big Island
during that time. The Flash Flood Watch may need to be extended
for eastern and possibly central parts of the state tonight, but
will wait to make that decision to see where showers and thunderstorms
remain this afternoon.

A Winter Storm Warning remains in effect for the Big Island summits
for through tonight. Satellite and radar shows deeper moisture
that will produce the snowfall approaching the Big Island at this
time. Strong winds will also cause significant blowing and drifting
of snow, along with very low wind chill readings.

A short break in the unsettled weather is expected from later
Monday through Tuesday as weak shortwave ridging builds over the
state and a somewhat less moist airmass passes through. However,
with light winds continuing, scattered showers will remain
possible along localized convergence zones such as afternoon
seabreezes. It appears that rain chances during this time will be
highest over the Big Island, and lowest over Kauai.

By Wednesday, global models continue to show another deep
mid/upper level trough developing west of the state, with a weak
surface trough over or just west of the islands. This will
maintain deep southerly flow over the islands, although surface
winds will remain rather light. Additional surges of deep moisture
with the potential for more heavy rains over the islands will be
possible during the second half of the week, although pinpointing
details of timing and location is not possible at these extended
time ranges. Overall, there is no indication of a return to quiet
trade wind weather anytime through the next several days.

&&

.AVIATION...
A swath of high clouds has spread across the islands, with a
variety of low and layered clouds, which are thickest over the
western end of the island chain this morning. The clouds and
accompanying showers are bringing periods of MVFR and occasional
IFR conditions, and some thunderstorms. AIRMET SIERRA is
currently posted for mountain obscuration on Kauai, and is
expected to be expanded to the remainder of the islands around
noon. Conditions should improve from west to east late today or
tonight.

AIRMET TANGO continues to upper level turbulence over the islands
in response to the upper level trough that is near Kauai. Expect
the turbulent conditions to continue throughout today and into
tonight as the trough slowly lifts away from the islands.

AIRMET ZULU remains posted for icing in the layered clouds
spreading across the region. An improvement is expected late
today or tonight from west to east.


&&

.MARINE...
Although light winds prevail across the Hawaiian coastal waters,
the nearshore buoys off Hanalei and Hilo continue to report seas
near 10 feet, while the buoys off Pauwela and Mokapu Point are
reporting somewhat lower seas. The appears to be due to a
combination of north and east swell. As a result, a Small Craft
Advisory for many of the coast waters zones remains in effect
through today. Seas should drop below 10 feet across the area by
tonight.

With seas at the Hilo buoy lingering near 10 feet early this
morning, the High Surf Advisory for east facing shores of the Big
Island remains in effect through today.

No large swells are expected so surf is expected to remain below
High Surf Advisory levels over the coming week.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch until 6 PM HST this evening for all Hawaii
islands.

High Surf Advisory until 6 PM HST this evening for east facing
shores of the Big Island.

Winter Storm Warning until 6 AM HST Monday for Big Island
Summits.

Small Craft Advisory until 6 PM HST this evening for Kauai
Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-
Kauai Channel-Oahu Windward Waters-Kaiwi Channel-Maui County
Windward Waters-Alenuihaha Channel-Big Island Windward Waters.

&&

$$

DISCUSSION...Foster
AVIATION...M Ballard
MARINE...Kodama



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