Strong Wind in Hawaii, November 22, 2020

Area Forecast Discussion
National Weather Service Honolulu HI
946 AM HST Sun Nov 22 2020

.SYNOPSIS...
Breezy to locally windy trades and wet weather will persist
across much of the state today. Trade winds will gradually
decrease Monday through Wednesday as surface high pressure
passing north of the islands moves off to the east. 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...
Strong trade winds will hold today, and wet conditions over
windward slopes of the Big Island and Maui will continue. The
trades are being driven by a 1032 mb centered roughly 1100 miles
north-northeast of the state. The high will drift eastward today,
maintaining the breezy to locally windy trades and keeping a Wind
Advisory in effect for portions of the Big Island and Maui
County. It was a rather wet night, and the strong trades carried
periods of showers from windward slopes to leeward areas of most
islands. The trade wind flow has dried out slightly for Kauai and
Oahu, where showers should be largely confined to windward terrain
today. However, a band of moisture remains focused across the
eastern end of the state. This feature is centered on the Big
Island, where the strong trade winds have been pushing persistent
showers up windward slopes all the way to the high summits. Expect
continued active showers for windward Big Island and Maui today.
In addition, a band of high clouds will move over from the west,
filtering the sunshine.

Trade winds will gradually decline during the first half of the
work week, while showers will remain active over portions of the
state. The high currently centered north-northeast of the islands
will continue to drift eastward, allowing the local pressure
gradient to relax and trade winds to slowly decline. That said,
it will still remain breezy and gusty on Monday into Tuesday. The
GFS and ECMWF show that the band of moisture will remain focused
across the eastern end of the state through Tuesday, favoring
continued wet windward conditions on the Big Island and Maui.
Showers may become enhanced across the western end of the state
Monday night and Tuesday and across the entire state Tuesday
night and Wednesday as an upper level trough passes overhead.
With the upper level trough nearby, expect periods of high clouds
to thin out on Wednesday.

Drier and more stable trade wind weather is expected on
Thanksgiving and Friday. The upper level trough will swing east
of the islands, allowing a mid level ridge to move in from the
west. This will cap and moderate showers and keep them largely
confined to windward slopes. Surface high pressure will build to
the northwest, leading to a gradual increase in trade winds.

Trades will likely increase heading into next weekend. The
building trades may push a dissipating front over the islands on
Saturday, leading to a period of increased in showers.

&&

.AVIATION...
A strong 1032 mb surface high lies 970 nm NNE of Oahu this
morning. It will moving E over the next couple of days, only to
be taken over by a new high on Tuesday. The trade winds will be
at their strongest for the next 12 hours or so, followed by a
slight weakening trend into Monday. AIRMET Tango for low-level
mechanical turbulence below 9k feet will continue through at least
tonight.

The leading edge of an east to west oriented band of clouds and
showers is aimed at Maui and the Big Island this morning. Low
ceilings and showers continue to impact north and east facing
sections of those islands, where AIRMET Sierra is in effect for
mountain obscuration. The AIRMET will likely hold into, or
possibly through, this afternoon if showers continue.

High cirrus clouds will be spreading across the island skies this
morning, from the W and SW, becoming thicker after 20Z.

&&

.MARINE...
Trade winds will remain strong over rough seas through Monday. A
Small Craft Advisory (SCA) is in effect for all waters with the
exception of the Alenuihaha Channel where a Gale Warning is in
effect. The SCA and Gale Warning are in effect through Monday
morning. Strong trades have produced rough seas with high surf
occurring along eastern facing shores. Thus, a High Surf Advisory
is in effect for all east-facing shores until Monday. Trades will
weaken and seas will lower from tonight through the middle of the
week. This will likely end the all-water SCAs and lower the
Alenuihaha Channel Gale Warning to an SCA Monday morning.

An arriving northwest swell will peak north and west-facing shore
surf from this afternoon through Monday morning. Elevated east-
facing shore surf will remain at High Surf Advisory levels
through Monday. Swell will subside through the week. A late week
arriving northwest swell will provide a boost to north and west-
facing shoreline surf. South-facing shore surf will remain small
through the week.

&&

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

Wind Advisory until 6 PM HST this evening for Molokai Windward-
Kahoolawe-Maui Leeward West-Maui Central Valley-Windward
Haleakala-Leeward Haleakala-South Big Island-Kohala-Big Island
Interior.

Small Craft Advisory until 6 AM HST Monday 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 AM HST Monday for Alenuihaha Channel.

&&

DISCUSSION...Wroe
AVIATION...TS
MARINE...Blood