923
FXHW60 PHFO 040638
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
838 PM HST Sat Oct 3 2026

.SYNOPSIS...

Limited showers windward and mauka into next week as moderate
trades become breezy tonight into Sunday night. More widespread
rain develops over the western end of the state by Wednesday.
Periods of heavy rain will be possible over and around Kauai and
potentially Oahu during the second half of the week.

&&

.SHORT TERM UPDATE...
Isolated light trade showers were seen on radar this evening, but
only on windward and mauka areas. Winds were averaging 5 to 15
mph, with gusts to 20 mph in the typical windier spots. The
forecast is on track and no update is needed at this time.

&&

.PREV DISCUSSION...
Issued at 254 PM HST Sat Oct 3 2026

Today through Tuesday.
Stable, moderate trades prevail as the state remains under
prominent mid-level ridging and is no longer enveloped in the
moist SE flow trailing Hurricane Nolo. The inversion hovers around
8kft at Hilo but is rather ill-defined at Lihue courtesy of a
sheared out upper wave that is slowly migrating past the state.
Breezy trades develop tonight through Sunday night in response to
a weak tropical disturbance that is advancing westward well south
of the state. Limited coverage of windward and mauka showers
during this time. By Tuesday, the gradient may be sufficiently
weak to support sea breeze development and attendant development
of afternoon showers over island interiors.

Wednesday through Saturday.
Excellent consensus exists among the guidance that a very deep
and early-season mid-latitude trough will extend south into the
subtropics and be on the doorstep of Kauai by Wednesday morning.
Cyclogenesis will occur around 30N latitude to the NW of Kauai
causing deep layer flow to veer to southerly. This southerly flow
is modeled to entrain the aforementioned tropical disturbance
(presently around 14N/150W) providing a boost to a plume of deep
tropical moisture that will be drawn northward Wednesday night
into Thursday. Characterized by PWATs of 2" or higher and
dewpoints in the 70s, this airmass will easily support areas of
heavy rainfall. Divergence within the right entrance of a strong
upper jet is modeled to be outstanding over the western end of the
state as this moisture advances northward while mid-level forcing
for ascent remains rather broad and lacks focus. Nonetheless,
deep layer ascent beneath the right entrance should be adequate to
maintain a decent coverage of showers during this time. The GFS
suggests that mid-level entrainment of dry air will maintain
higher stability and limit potential for deep convection while the
EC considerably more aggressive with its depiction of actual
rainfall. Either way, limited availability of conditional
instability and paltry mid- level lapse rates will keep updraft
intensity in check and will limit potential for thunder.

Model consensus breaks down during Thursday owing to the 12z GFS`s
depiction of a suspiciously intense and compact surface low. This
low then quickly occludes and wraps westward beneath the upper low
allowing trades to aggressively return as early as Thursday night.
The EC`s depiction is considerably more reasonable and suggests a
longer-lived threat for heavy rain and flash flooding potential
still focused mainly on Wednesday night through Thursday for Kauai
and Oahu but then potentially lingering over Kauai into the weekend.
The 18z GFS has trended toward the EC`s surface low depiction and
consequently favors a longer lived event and increases confidence in
this diagnosis. A Flood Watch may eventually be needed for this time
period for Kauai and/or Oahu.

&&

.AVIATION...
Moderate trades through the period. Windward and mauka SHRA
possible. MVFR conds in SHRA otherwise VFR prevails.

AIRMET Sierra is in effect for mtn obsc for windward Big Island.
Conds should improve in the mid morning hours.

&&

.MARINE...
Moderate to locally fresh trade winds will build in this evening
as the high pressure strengthens to the north. A Small Craft
Advisory goes into effect this evening for the windier waters and
channels around Maui County and the Big Island through Sunday
afternoon and may need to be extended. Locally strong trades may
persist into early next week before high pressure to the north
weakens again and winds start to diminish. By the middle of next
week, troughing developing northwest of the islands may cause
winds to veer out of the southeast once again.

Surf along south-facing shores will steadily decline through the
weekend. A new small, long-period south swell, originating from a
large fetch of gale force winds southeast of New Zealand earlier
this week, is expected to slowly fill in Sunday evening and peak
Monday through Wednesday. This will push surf to slightly above
seasonal averages for the first half of next week.

A small bump in surf along north-facing shores will fade tonight.
Another small bump in north shore surf is possible early next
week as a small, medium-period northwest swell arrives late Sunday
and peaks on Monday. This will be followed by a slightly larger
long-period northwest swell peaking on Wednesday, giving a good
boost to north shore surf for mid-week. Surf along east-facing
shores will increase and become more choppy tonight as easterly
trades build back into the region.

&&

.FIRE WEATHER...
Issued at 254 PM HST Sat Oct 3 2026
Moderate trades will become breezy tonight through Sunday night as
drier air works into the area during the day tomorrow. RH values
are forecast to hover just above the critical threshold for fire
weather but may nonetheless approach it during the afternoon. Fire
weather risk then diminishes through the remainder of the week as
moisture increases, winds decrease, and showers increase in
coverage especially over the western end of the state. The
inversion will range from 6kft to 8kft for the next couple of
days.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Sunday for Alenuihaha
Channel-Big Island Leeward Waters-Big Island Southeast Waters-
Maalaea Bay-Pailolo Channel.


&&

$$

SHORT TERM UPDATE...Parker
DISCUSSION...JVC
AVIATION...Walsh
MARINE...Quesada