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Hawaiian Islands Synoptic Discussion and Guidance

946
FXHW60 PHFO 291959
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
959 AM HST Sun Nov 29 2020

.SYNOPSIS...
An upper level disturbance drifting through the region will
produce showery trade wind weather through tonight with an uptick
in showers expected this afternoon and evening. Weather will begin
to shift on Monday with winds becoming light and variable and a
drier air mass moving in Monday night. A land/sea breeze regime
is expected through around midweek, with light trades possibly
returning as early as Wednesday and becoming breezy on Friday.
Also, an increase in moisture is expected Thursday mainly across
Maui county and the Big Island as a weak trough moves in from the
east.

&&

.DISCUSSION...
An upper level trough swinging through the state later today will
bring increasing showers and isolated thunderstorms over parts of
the state. The best chance for thunderstorms will be over the
eastern half of the state with the threat of locally heavy
rainfall this afternoon through the overnight hours.

As the upper level trough begins to move east and away from the
state late Sunday night into Monday, we will see the atmosphere
stabilize with showers on the decrease across the state. Trade
winds will also relax and become light and variable by Monday
afternoon. This will allow for the development of sea breezes in
the afternoon and will likely produce clouds and showers over
interior areas of the islands. Lingering instability across the
eastern end of the state could produce a few thunderstorms over
the slopes of the Big Island during the afternoon.

A dry airmass will move in across the state Monday night and will
bring mostly clear conditions through Tuesday. With the clear
conditions, we should see fairly cool overnight/morning
temperatures Tuesday morning.

For the second half of the week, a weak ridge just north of the
state could bring the return of light trades as early as
Wednesday. Trades will likely be light enough for the development
of land and sea breezes through Thursday. Also, a weak trough
approaching the state from the east will bring an increase of
moisture over the eastern half of the state on Thursday. Locally
breezy trades are expected to return on Friday as a high builds
north of the state.


&&

.AVIATION...
Showers embedded within moderate trades are bringing periodic
showers and mountain obscuration to the Islands this morning.
Deeper convection, including isolated thunder, is noted northeast
of the state. This convection is aligned along the lead edge of
an a compact upper low that will move through the state today.
Iso-sct heavy showers will therefore be possible from Oahu
through Big Island this afternoon with isolated thunderstorms as
far north as Molokai. Pockets of heavier showers capable of
producing MVFR or localized IFR will be possible through tonight.
Trades are forecast to quickly weaken through Monday potentially
giving way to sea breezes by afternoon.

AIRMET Sierra for tempo mountain obscuration remains in effect for
Kauai through Maui.

AIRMET TANGO for tempo mod turb between FL180/270 remains in
effect for the entire area.



&&

.MARINE...
Light to locally moderate trade winds are expected today as weak
high pressure lies far north of the area. A series of fronts will
be passing by north of the area over the next several days
resulting in rather light easterly flow with land and sea breezes
setting up across most areas. These lighter winds will continue
through Thursday.

Surf along north facing shores will remain up today due to a mix
of north northeast and north northwest swell energy moving through.
Another small north northwest swell, will fill in Sunday night and
Monday before lowering on Tuesday.

A hurricane force low, far northwest of the state, will produce a
very large swell that will impact the state. Long period forerunners
will build during the day Tuesday. With swell periods exceeding
20 seconds, there will be likely long lulls between sets creating
the potential for sneaker waves. This swell will continue to build
Tuesday night into Wednesday producing warning level surf along
most north and west facing shores. Tides are currently running
about half a foot above predicted levels based on a tide gauge at
Honolulu Harbor. This combined with high monthly astronomical
tides, will further increase the possibility of runup on roadways
and other low lying areas during the peak of this event.

A Small Craft Advisory will also be needed for the coastal waters
as seas exceed 10 feet as early as Tuesday afternoon for waters
near Kauai, then quickly spread to other exposed waters Tuesday
night and Wednesday. This swell will then lower gradually Wednesday
night through Friday. A new, moderate size north northwest swell
is expected to fill in Friday night and Saturday.

Short period surf along east facing shores will drop off early
this week as trade winds diminish. Some eastern shorelines with
northern exposure may see some wrap around surf from the large
northwest swell this week. Only background southerly swells are
expected throughout the forecast period.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$


DISCUSSION...Kino
AVIATION...JVC
MARINE...Burke

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



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