High Wind in Hawaii, August 7 to 9, 2023

Area Forecast Discussion
National Weather Service Honolulu HI
913 PM HST Sun Aug 6 2023

.SYNOPSIS...
Moderate to breezy easterly trade winds are forecast to become
strong and gusty late Monday through midweek as Hurricane Dora
passes far to the south. After a few windward showers continue
overnight into Monday, very dry air arriving from the east will
limit rainfall chances Monday through Wednesday. A return of a
more typical trade wind pattern is anticipated Thursday through
the weekend.

&&

.DISCUSSION...
An upper low nearby to the northwest combined with a mid-level
trough and a sufficient amount of low-level moisture will support
scattered light showers favoring windward and mountain locations
continuing into Monday. Satellite imagery showed the leading edge
of a very suppressed and dry airmass approaching from the east,
which marks where the easterly wind surge is located. This drier
air (PWs dipping well below normal) combined with a strong
pressure gradient between Dora passing to the south and high
pressure to the north will support strong and gusty winds late
Monday through midweek. The subsidence inversion is forecast to
dip to around 3000 ft, which is well below normal. This stable/dry
air and low inversion combined with the strong pressure gradient
(50 kt winds shown around the inversion to 850 mb) will support
advisory to warning-level wind speeds late Monday through
Wednesday.

For the second half of the week through the weekend, expect a
return of a more typical trade wind pattern, with windward and
mountain shower coverage increasing.

&&

.AVIATION...
Surface high pressure well to the northeast of the state will
continue to help generate moderate trades across the islands
tonight through Monday morning. Some low level moisture caught up
in the flow will bring scattered to numerous showers to the
windward sides of the islands. Brief periods of MVFR ceilings and
visibility may accompany this activity. Elsewhere, expect isolated
showers. By Monday afternoon, drier air is forecast to filter
into the region and allow shower chances to dwindle.

A tight pressure gradient will develop across the region late
Monday through Wednesday, due to the combination of strong surface
high pressure north and Hawaii and Hurricane Dora passing well
south of Hawaii. This scenario will create strong a gusty trades
across all islands from during the aforementioned period.

There are currently no AIRMETs in effect. However, AIRMET Tango
for moderate turbulence downstream of terrain is expected on
by Monday afternoon due to the strengthening trade winds.

&&

.MARINE...
Trade winds will strengthen through Tuesday as the ridge builds
north of the islands and Hurricane Dora passes south of the
Hawaiian Islands from Monday afternoon through Wednesday morning
on its westward track. Wind speeds will peak on Tuesday with a
Gale Warning in effect over the windier channels and waters around
Maui County and the Big Island, from Monday morning through
Tuesday night. Strong wind speeds and rapidly building rough seas
will occur over the rest of the coastal waters from Monday through
Tuesday night as well. A Small Craft Advisory remains in effect
for the remaining coastal waters.

Surf along east facing shores will quickly ramp up and become
rough through Wednesday due to a combination of very strong
trades, large seas and a moderately sized, moderate period
easterly swell generated from Dora. The largest surf is expected
over the eastern end of the state, where surf heights may approach
warning levels late Monday through Tuesday night. A downward trend
is expected Wednesday through Thursday as trade winds and seas
diminish to more typical conditions.

Surf along south facing shores will remain small through Monday with
background south and southwest swell energy rolling through. A
short to medium period southeast swell will fill in on Tuesday
from Dora as it passes by far to the south. This will be a short
lived event with a peak occurring late Tuesday into early
Wednesday. A small, long period south-southwest swell from the
South Pacific will arrive by Wednesday, south shore surf heights
will approach advisory thresholds from Wednesday into Thursday,
before diminishing through the end of the week.

&&

.FIRE WEATHER...
Critical fire weather conditions are highly likely beginning
Monday. Dry, stable, and strong and gusty trades are expected as
deep high pressure to the north moves in tandem with Hurricane
Dora, which is forecast to pass well south of the islands.
Conditions could develop as early as Monday, but Tuesday has the
greatest potential as the Keetch Byram Drought Index (KBDI) is
expected to reach near or just above the 600 mark. Additionally,
models show leeward relative humidity falling below 45 percent. A
Fire Weather Watch is now in effect from Monday morning through
late Tuesday night for leeward portions of the islands, where
critical fire conditions are most likely to develop.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Monday morning through late Tuesday
night for Kauai Leeward-Oahu South Shore-Waianae Coast-Oahu
North Shore-Olomana-Central Oahu-Waianae Mountains-Molokai
Leeward-Lanai Makai-Lanai Mauka-Maui Leeward West-Maui Central
Valley-Leeward Haleakala-Kona-South Big Island-Kohala.

High Wind Watch from Monday morning through late Tuesday night
for Kauai Leeward-Kauai Mountains-Waianae Coast-Oahu North Shore-
Olomana-Central Oahu-Waianae Mountains-Lanai Mauka-Kahoolawe-
Maui Windward West-Maui Leeward West-Haleakala Summit-Kohala-Big
Island Interior-Big Island Summits-Kauai North-Kauai South-East
Honolulu-Honolulu Metro-Ewa Plain-Koolau Leeward-Molokai-Lanai
Windward-Lanai Leeward-Lanai South-Maui Central Valley North-
Maui Central Valley South-South Maui/Upcountry-South Haleakala-
Big Island South-Big Island Southeast-Big Island North.

Gale Warning from 6 AM Monday to 6 AM HST Wednesday for Maalaea
Bay-Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-
Big Island Southeast Waters.

Small Craft Advisory from 6 AM Monday to 6 AM HST Wednesday for
all remaining Hawaiian waters.

&&

DISCUSSION...Vaughan
AVIATION...Kino
MARINE...TS
FIRE WEATHER...Vaughan