Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 040621

Area Forecast Discussion
National Weather Service Honolulu HI
821 PM HST Sun Dec 3 2023

Dry and stable trade wind conditions are expected through the
first half of the week, with the best rainfall chances favoring
our windward and mauka locations overnight through the morning
periods. A few showers could make it into our leeward areas,
especially as the trades become gusty Monday night through
Tuesday. A return of light winds and increasing moisture
associated with an approaching front could bring the rainfall
chances up late Thursday through the weekend, especially over the
western end of the state as the front begins to weaken and stall.


Guidance remains in good agreement and shows a return of a more
typical trade wind pattern through the first half of the week as a
strong ridge noses eastward behind a passing front north of the
state. Clouds and showers will shift back over windward and
mauka locations, with the best chances being overnight through
the early morning hours. Although the tail-end of the front should
stall and dissipate nearby to the north Tuesday through
Wednesday, the leading edge of the moisture axis could make it as
far south as Kauai Tuesday, which would support better windward
shower coverage. Elsewhere, dry and stable conditions will limit
rainfall accumulations. Easterly trades are expected to peak in
the breezy category Tuesday as strong high pressure builds to our

Despite some model differences in timing, a general consensus
supports the ridge to the north weakening and shifting southward
beginning Thursday as a shortwave trough and surface cold front
approach. Surface winds will respond and become light out of the
southeast Thursday as the front moves into the area. A combination
of light winds, increasing moisture, and lowering upper heights
will support better rainfall coverage over the western end of the
state where the front will weaken and begin to stall. Light winds
may linger into the weekend before trades gradually return Sunday
into next week.


A high pressure system will build in north of the state through at
least Tuesday with increasing trade winds into the moderate to
locally breezy range starting on Monday. Brief periods of isolated
to scattered showers are expected mainly over windward and
mountain areas. Periods of MVFR ceilings and visibility are
likely to persist this evening along windward Big Island with
pockets of IFR conditions. Windward Big Island weather conditions
will begin improving after 10Z.

AIRMET SIERRA remains in effect for north through east sections of
the Big Island for tempo mountain obscuration above 1500 feet due
to clouds and showers. These conditions will likely to slowly improve
after 10Z.


Weak ridging north of the state has maintained a lax pressure
gradient over the local waters. This synoptic scenario will
result in a continued gentle trade wind regime tonight. A better
established area of high pressure northwest of the islands builds
in behind a hurricane force low near 48N154W that is currently
tracking east across the North Pacific and into the Gulf of Alaska
through early morning. This set up will tighten the pressure
gradient down across the region and ultimately restrengthen trades
from fresh to locally strong magnitudes by Tuesday afternoon.
These speeds will hang on through Wednesday before backing off
again in response to the high north of the islands moving east and
being replaced by a relatively small weak area of low pressure.
This low may be far enough south to drag a very weak, diffuse
boundary into the waters by next weekend. A large swell created by
the hurricane force low will reach our offshore waters tomorrow
and likely prompt an all water Small Craft Advisory (for seas).
This will occur just before the period of strong winds commences
tomorrow night into early Tuesday across the typical windier
waters surrounding Maui County and Big Island.

The High Surf Advisory (HSA) remains in effect for the north and
west-facing shores of the smaller islands, except Maui`s west
shore, through tomorrow afternoon. This is associated with an
ongoing passing northwest (320 degree) long period swell that will
hold and subside very little through the day tomorrow. Today`s
nearshore buoy observations and surf observations have indicated
that this long to medium period near 7 foot swell peaked today and
resulted in HSA level surf. The next north northwest (330-350
degree) swell will be on the heels of this ongoing swell,
generated from the hurricane force low mentioned above, and is
scheduled to arrive late tomorrow and peak on Tuesday. This large,
long period swell will likely drive surf heights to above High
Surf Warning thresholds Tuesday. This large swell should slowly
decline from Tuesday night through the remainder of the week as it
veers more northerly. Strengthening trades should increase
eastern exposure chop and lead to rough surf from Tuesday into the
middle of the week. Small background swell leading to very small
surf will continue along south-facing shores throughout the week.


High Surf Advisory until 6 PM HST Monday for Niihau-Kauai
Leeward-Waianae Coast-Oahu North Shore-Kauai North-Molokai
Windward-Molokai North-Molokai West-Maui Central Valley North-
Windward Haleakala.

Small Craft Advisory until 6 PM HST Monday for Kauai Northwest
Waters-Kauai Windward Waters-Oahu Windward Waters-Kaiwi Channel-
Maui County Windward Waters-Alenuihaha Channel-Big Island
Windward Waters.



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