Gale Warning 8, NWS Honolulu, HI

Area Forecast Discussion
National Weather Service Honolulu HI
931 AM HST Tue Dec 10 2024

.SYNOPSIS...
Strong trades focus limited showers windward and mauka through
Thursday. Trades then ease for the weekend.

&&

.DISCUSSION...

The islands reside near the inflection point between strong mid-
level ridging anchored immediately west of the islands and troughing
to the east. Breezy trades prevail at the surface with the greatest
stability characterized by a strong inversion at 5kft over Kauai.
The inversion slopes upward to 8kft at Hilo in closer proximity to
the deepening mid-level trough axis. Morning visible imagery shows
cloud streets oriented parallel to the flow containing the
occasional line of training light showers, but the generally dry
pattern persists.

The aforementioned trough axis is closing off this morning and will
deepen south of the area as it advances westward through mid-week
before dissipating on Friday. This trajectory will focus pressure
falls south of the island chain as mid-level ridging builds over and
north of the forecast area, though the Big Island will remain within
the envelope of cyclonic flow aloft through Thursday. This in turn
results in steadily strengthening deep layer easterlies today into
Wednesday for which a Wind Advisory remains in effect for portions
of Maui County and the Big Island. This advisory remains in effect
through Wednesday. As the gradient over the area strengthens during
the next 24 hours, so too will trades. Strong trades then hold
through Thursday before weakening in response to the dissipating
low. Current wind observations are generally tame, though a few peak
values are noted in preferred downslope locations such as
observations such as sustained 25 kts at the HELCO Kawaihae Rd
station in the Big Island's Kohala District and 41 kts at the MECO
Kealaloloa on Leeward Maui. This is in line with recent WSR-88D VAD
wind profiles which generally indicate an upper end of around 35 kts
in the lowest few thousand feet over the eastern end of the state.
As the low deepens during the next 24 hours or so, this strong wind
field will expand northward encompassing the remainder of the state
with borderline Wind Advisory conditions for Molokai through Kauai
possible Wednesday and Thursday. Model projections suggest 925mb
winds no higher than about 35 kts for gust potential which limits
confidence for the issuance of any additional wind headlines at this
time. Easterlies on the Big Island summits may reach High Wind
Warning (56+ mph) thresholds tonight while low potential exists for
winds to approach the advisory threshold for Haleakala Summit (45+
mph) during the same time.

The northern envelope of mid-level cyclonic flow will remain over
the Big Island through Thursday, eventually extending as far down as
850mb. This will in turn draw deeper moisture northward resulting in
enhancement of trade wind showers there, especially Wednesday and
Thursday night.

&&

.AVIATION...

Strong trade winds will continue to strengthen in the short term,
delivering randomly distributed low cloud clusters that will
briefly drop a few showers windward, producing ISOL MVFR VIS/CIG.
AIRMET Tango will remain posted for low-level turbulence to the
lee of the terrain.

&&

.MARINE...

trong high pressure to the north and northeast of the islands
will continue to build and expand westward. Easterly trade winds
will strengthen to become locally strong by this afternoon, then
persist through Thursday and possibly beyond. Speeds may approach
near-gale, or possibly even gales in the windier channels from
tonight through tomorrow night. As trades strengthen, seas will
also be on the rise to near or above 10 feet today. A Small Craft
Advisory (SCA) remains in effect for all waters through Thursday
due to a combination of winds and seas.

Surf along north and west-facing shores is expected to peak late
this afternoon or early evening as a northwest reinforcement moves
through the islands. Offshore buoy 51001 has generally been
rising throughout the morning, from near 8 feet around 3am HST to
11 feet at 9am HST, indicating an expected increase in surf
heights later today for affected shores of the smaller islands. A
High Surf Advisory (HSA) remains in effect for north and west
facing shores of Niihau, Kauai, Oahu, and Molokai, and north
facing shores of Maui through tonight. North and west shore surf
will then gradually decline through the end of the week.

Surf along south-facing shores will subside today. Seasonal
conditions are expected to return tomorrow, with smaller southeast
and south-southwest swells contributing to surf conditions

Surf along east-facing shores will rise through Thursday in
response to the strong trade winds. Lower surf is expected for
the weekend.

&&

.FIRE WEATHER...
Strong trades and marginally dry conditions warrant continued
monitoring for potential fire weather conditions on Wednesday and
Thursday. Although dewpoints may fall as low as the low 60s each
afternoon, seasonably cool high temperatures in the low/mid 80s
limits confidence in reaching the 45% RH threshold.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Wednesday for Niihau-Kauai
Leeward-Waianae Coast-Oahu North Shore-Maui Windward West-Kauai
North-Molokai Windward-Molokai North-Molokai West-Maui Central
Valley North-Windward Haleakala.

Wind Advisory until 6 PM HST Wednesday for Lanai Mauka-Kahoolawe-
Maui Windward West-Maui Leeward West-Kohala-Big Island Interior-
Lanai Windward-Lanai Leeward-Lanai South-Maui Central Valley
North-Maui Central Valley South-South Haleakala-Big Island South-
Big Island Southeast-Big Island North.

Wind Advisory until 6 PM HST Wednesday for Big Island Summits.

Small Craft Advisory until 6 PM HST Thursday for all Hawaiian
waters-

&&

DISCUSSION...JVC
AVIATION...Birchard
MARINE...Vaughan