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Hawaiian Islands Synoptic Discussion and Guidance

767
FXHW60 PHFO 290624
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
824 PM HST Wed Oct 28 2020

.SYNOPSIS...
A front over Maui County will stall and dissipate by tomorrow. Spotty
heavy showers will continue along and southeast of the front.
Northwest winds behind the front will bring less humid conditions
and will push shallow shower bands over the islands through the
weekend. A ridge will build north of the islands by Monday and
bring a return of trade winds.

&&

.DISCUSSION...
A front over Maui County will stall tonight then weaken over the
next 36 hours. Showers will likely remain concentrated along the
weakening front, but locally breezy westerly winds will also bring
a few showers to most islands, especially along leeward (west
facing) slopes. On Friday, these winds could become gusty over
some windward (east) areas as the winds blow downslope. There
will noticeably drier air behind the front.

During the weekend, the low will lift off to the northeast. Northwest
to north flow south of the low will continue to carry bands of
showers over the islands. A trough aloft digging south over the
area could enhance showers on Sunday.

The global models are in good agreement showing a surface ridge building
north of the islands by Monday. The ridge will produce easterly
trade winds over the islands.

&&

.AVIATION...
Clouds and showers (some locally heavy with a slight chance of a
thunderstorm) will continue to develop along a ENE-WSW front
currently draped over Maui County. Isolated IFR VIS/CIG and TEMPO
MVFR VIS/CIG can be expected with this convection, with the front
expected to move slowly SE and gradually weaken through Thursday.
AIRMET SIERRA is currently posted for Oahu and Maui County as a
result, but conditions may improve over Oahu shortly. A stable
post-frontal NW flow over Kauai will spread to Oahu overnight,
leading to improving conditions.

&&

.MARINE...
A weakening front over Maui County will stall and dissipate near
Maui or the northern Big Island on Thursday. Light to moderate
south to southwest winds will persist just ahead of the front over
the waters surrounding the Big Island through Thursday. West of
the front, expect moderate west winds over the waters adjacent to
Kauai, Oahu, and most of Maui County. In addition to the winds,
locally heavy showers and a slight chance of thunderstorms remain
possible along and ahead of the front into early Thursday morning.
Expect this general wind pattern to continue into the weekend as
a new trough moves into the area from the northwest. Trade winds
may return early next week as a surface ridge develops north of
the state.

The current north-northwest swell is expected to gradually
diminish tonight. A new short-period, moderate north-northwest
swell associated with the fetch from a surface low pressure
system located north of the islands is expected arrive by
early Thursday. This swell will gradually build from late
Thursday through Friday, and cause surf to increase over most
north facing shores, with the highest surf expected along
northern exposures of Kauai and Oahu. This north-northwest swell
will gradually lower from Friday night into the weekend.
Forerunners from a new long-period northwest swell are expected
to arrive on Saturday. This swell will likely continue to build
to moderate heights, and shift around out of a north-northwest
direction from Saturday night through Sunday. Yet another long-
period north-northwest swell is expected to spread down across
the area from late Sunday night through Monday. This swell will
linger early next week.

Surf along south facing shores will remain small through this
weekend due to a combination of background short-period,
southeast and long-period, small south and southwest swells. An
upward trend in surf along south facing shores is possible next
Wednesday due to a new long-period south swell.

The current northeast swell will continue to steadily trend down
through Thursday. Another small northeast swell may arrive
Thursday night into Friday. These swell sources will maintain
tiny surf along east facing shores during the next few days.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory through 6 PM Friday for the summits of Mauna Kea and
Mauna Loa on the Big Island.

&&

$$
DISCUSSION...Donaldson
AVIATION...Birchard
MARINE...Houston

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