539
FXHW60 PHFO 110103
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
303 PM HST Wed Dec 10 2025

.SYNOPSIS...
A front will bring a round of showers to Kauai tonight and Oahu
early Thursday before stalling over Maui County during the day.
Limited rainfall is then expected through Saturday before a
stronger front brings heavy rainfall potential to the western end
of the state Sunday through Tuesday.


&&

.DISCUSSION...
Dearth of moisture over the islands this afternoon as evidenced by
clear to partly cloudy skies over area waters and very dry
soundings out of both Lihue and Hilo. At press time, strongly
stable conditions prevail with an inversion around 5kft. Visible
satellite indicates a decaying cold front advancing toward Kauai
in response to a baroclinic frontal wave deepening well north of
the islands. Satellite observations put upstream shower tops
around 11kft which closely matches the modeled moisture depth as
this shower band moves into the island chain tonight.

Tonight. With the parent trough already departing to the northeast,
this feature will have no upper support and will instead move into
the forecast area against a background of mid-level height rises and
general large scale subsidence. A few leeward showers will be
possible within southerly flow ahead of the front, but the
convergent frontal axis itself and trailing NW winds will serve as
the focus for the bulk of rainfall which along exposed slopes late
this evening (Kauai) through early tomorrow morning (Oahu). Stout NW
flow will rapidly weaken as it veers to NNE during Thursday.
Consequently, showers may hang up along the northern slopes of Kauai
for a time, but the diminishing gradient combined with crashing post-
frontal dewpoints in the 50s should inhibit potential for any stream
rises there as shower intensity and coverage behind the front
quickly wind down.

Thursday through Saturday night. Lack of large scale forcing causes
the front to stall over Maui County on Thursday while the rapidly
diminishing pressure gradient allows potential for a transition from
windward showers to interior showers as afternoon sea breezes
develop, mainly over interior Maui. A few afternoon showers will
also be possible over Oahu since the punch of dry air will struggle
to push that far east. Overnight land breezes bring drying to all
islands on Thursday night. The remainder of this time period will
generally be dry, though moderate southerlies threaten to push the
occasional shower over leeward zones of Kauai through Maui. By
Saturday night, isentropic ascent associated with the approach of a
much deeper upper trough will gradually saturate the mid-levels,
though soundings are modeled to be initially disjointed courtesy of
a stable dry layer anchored around 10kft. This will favor limited
shallow leeward showers coupled with a developing layer of
stratiform rain aloft, most likely centered between Kauai and Maui.
Any rainfall through Saturday night is forecast to be modest.

Sunday through Tuesday. This period represents a transition to a
more dynamic pattern. A second remnant front, not dissimilar from
the current one, will advance into the western portion of the state
during Sunday providing a boost to low-level moisture and possibly
allowing for some coupling with the aforementioned layer of
deepening mid-level moisture by Sunday afternoon. Outstanding right
entrance jet support associated with a SWly 135kt jet then spreads
over the area late Sunday as the upper trough approaches. This in
turn deepens the existing cold front as healthy fgen develops
through the column. The resulting mature jet-front system will be
accompanied by a narrow corridor of strong uplift that will support
a band of heavy rain somewhere over the western end of the state
Sunday night through Monday night. The parent trough remains rather
progressive suggesting a 24-36 hour type of event. Upon the
departure of supporting upper dynamics on Tuesday, the orphaned
frontal moisture band will once again stall over the area through
mid-week in maintenance of lingering showers over the area.
Southerly winds prevail throughout this time keeping leeward zones
in the game for rainfall for at least the next week.

Forecast reasoning for the extended remains unchanged. Blocking high
pressure over the Aleutian Island chain maintains a southward-
displaced Pacific jet stream that is modeled by the EC, GFS, and
machine learning guidance to settle into the low latitudes (20-25N)
by the end of the forecast period. This ensures at least some
potential for more active weather continuing for the foreseeable
future.


&&

.AVIATION...

South to southwest winds have strengthened across the state this
afternoon ahead of a cold front approaching from the northwest.
VFR conditions will continue to prevail into the early evening
hours as limited clouds and showers move in with the southerly
flow. The cold front is expected to reach Kauai early this
evening, Oahu early Thursday morning, and then slowly diminish
over Maui County. Along the front, showers will bring periods of
MVFR and even brief IFR conditions will be possible. Behind the
front, light to moderate northerly winds and VFR conditions are
expected.

No AIRMETs are in effect, but AIRMET Sierra for mountain
obscuration may be needed this evening through tomorrow morning
as the front moves from west to east over the smaller islands.


&&

.MARINE...

Light south southwesterly winds will be in place this afternoon
for all islands ahead of an approaching front from the northwest.
The front will enter the Kauai waters late tonight and move east
across the state through Thursday before stalling and dissipating
around Maui County Thursday night. An increase of showers are
expected along and ahead of the front with moderate northerly
winds following behind it. Another stronger front looks to
approach the islands from the northwest on Saturday afternoon
through Sunday and bring moderate to fresh south southwesterly
winds and increased rainfall over the western islands. Current
guidance suggests this front could stall near Kauai and linger
through next week.

A moderate, long period northwest swell (320 degree) will hold
before reinforcing north- northwest swell (330 degree) fills in
tonight and peaks Thursday morning. These swells will keep surf
elevated, therefore a High Surf Advisory for select north and
west facing shores remains in effect through Thursday. These
overlapping swells will slowly decline Thursday night into the
weekend. Another moderate, long period northwest swell (320
degree) should gradually fill in on Sunday and could produce surf
near the advisory threshold by Sunday afternoon. A combination of
small north swells and small west-northwest swells then look to
arrive next week.

East shore surf will remain small through the forecast period due
to the absence of trade winds. Expect minimal background surf for
south facing shores, with a minor south- southwest pulse expected
today into Thursday. South facing shores could receive small to
moderate choppy windswell Saturday through next week from the
southwest winds. This would depend on the location and strength of
the front, likely largest for southwest shores of Kauai.


&&

.FIRE WEATHER...
Conditions will remain below critical fire thresholds through the
week with light winds and elevated RH. The inversion will hold
around 5-6kft through tomorrow.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST Thursday 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.


&&

$$


DISCUSSION...JVC
AVIATION...Farris
MARINE...Tsamous
FIRE WEATHER...JVC