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RH58 %
WindNNE 2 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

610
FXHW60 PHFO 231401
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
401 AM HST Mon Nov 23 2020

.SYNOPSIS...
Breezy trade winds will persist through Tuesday, while gradually
diminishing. High clouds are expected to linger over the islands,
and trade winds will continue to focus showers over windward
areas. Showers will be more active on the windward slopes of the
Big Island and Maui today. As an upper level feature moves over
the islands tonight through Tuesday night, a few thunderstorms
will be possible. Moderate trade winds and a decrease in showers
are expected for most areas on Thanksgiving Day. Increasing trade
winds will likely push a dissipating front over the state on
Saturday.

&&

.DISCUSSION...
Have made some tweaks to the forecast throughout the forecast
period, but no major changes.

A band of moisture continues to ride in on the trade winds and has
been impacting primarily the Big Island and portions of Maui
overnight. The band extends several hundred miles to the east of
the Big Island, and is expected to continue to bring showers to
over the next couple of days. Most of the showers yesterday and
overnight have reached upslope, with lower rainfall totals at the
coast. Coastal areas are seeing an uptick in stream levels as the
result of the upslope showers, and this could cause some nuisance
flooding in and around Hilo as time goes on.

A 1032 mb high pressure system far north-northeast of the islands
will continue to bring breezy trade winds to the region today and
tomorrow. Winds have been gradually diminishing after the stronger
trades were seen over the weekend. Moderate trade winds are
expected to be found by Thanksgiving Day.

An upper level trough to the west of the islands is helping to
spread some high clouds over the islands from the west. This upper
level feature is expected to move to the east, and as it does so,
the bulk of the high clouds will shift to the south and east.

This upper level trough will be part of the catalyst for some
possible thunderstorms Monday night through Wednesday morning.
The area of thunderstorm possibility remains unchanged, and
follows closely the location of the upper level trough as it moves
in from the west and then stalls over the central islands
Tuesday night/Wednesday morning and weakens.

A drier and more stable airmass appears to move overhead for
Thanksgiving and Friday as the upper level trough moves east of
the islands. This will allow a mid level ridge to move over the
islands which will help cap the showers and largely confine them
to the windward sides of the islands. High pressure building to
the northwest will allow trade winds to gradually increase heading
into the weekend. The building trades may push a dissipating
front over the islands late Friday or Saturday, leading to a
period of increased in showers.

&&

.AVIATION...
A zonally oriented band of moisture will remain focused on the
Islands bringing periods of widespread MVFR and showers through
this morning, especially for windward areas. Some improvement is
likely this afternoon before conditions deteriorate again late
this evening. Gusty winds will also remain a focus of the
aviation forecast as strong trades will very gradually weaken
through the day.

AIRMET Sierra for mountain obscuration remains in effect for
Windward Oahu through Big Island.

AIRMET Tango for lee turbulence remains in effect for the entire
area.

&&

.MARINE...
A strong high far northeast of the area will maintain easterly
trade winds over Hawaiian waters through the week. The trades are
currently quite strong, with near gale force winds in the windier
areas around the Big Island. The strong winds plus a moderate
northwest swell are also producing seas above 10 feet. A Small
Craft Advisory is in effect for most waters from Oahu to the Big
Island. Winds will subside over the next few days as the high
weakens.

A long fetch of strong trade winds has generated large waves. A
High Surf Advisory is in effect through this evening for east
facing shores of all islands except Lanai and Niihau. Surf along
the east facing shores will subside over the next few days as the
trade winds weaken.

A moderate northwest swell that peaked overnight will subside
through Wednesday. A new moderate-sized northwest swell is
expected over the weekend. Some of the large trade-wind swell is
wrapping around into south facing shores. Otherwise, surf along
south facing shores will remain small through the week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST this evening for Kauai
Windward-Oahu Koolau-Olomana-Molokai Windward-Maui Windward West-
Windward Haleakala-South Big Island-Big Island North and East.

Small Craft Advisory until 6 PM HST Tuesday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

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

&&

$$


DISCUSSION...M Ballard
AVIATION...JVC
MARINE...Donaldson

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