392
FXHW60 PHFO 161425
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
425 AM HST Sun Nov 16 2025

.SYNOPSIS...
Light to locally breezy trades with generally drier weather
through Monday afternoon. Showers will focus along windward
exposed upslope terrain the next couple of days. There are
increasing chances for more active weather from late Monday
through Thursday with higher probabilities for locally heavy
rain with isolated thunderstorms.

&&

.DISCUSSION...
Broad upper ridging across the West Central Pacific has expanded
just far enough east, along with a swath of drier air passing by
from the east, to influence and stabilize our weekend weather
here in paradise. Morning shortwave IR satellite is depicting a
lower level moist air mass advancing in on light to moderate
trades. This will increase overall precipitation coverage today
but most of the light showers will briefly pass over windward
communities with the highest precipitation being confined to the
upper elevations. A weakened 1022 mb surface high pressure located
approximately 1,000 miles northeast of Hilo is slowly settling
southeastward. This has sustained a tight enough downstream
pressure gradient to support light trades the next couple of days.
Local 12Z soundings are still showing a 6-7k ft boundary layer
underneath very dry mid to upper level air. These factors equate
to another couple of days of primarily dry, stable weather under
partially sunny skies and light trades, locally breezy within
higher terrain. Light precipitation will again focus along
windward upslope mauka. Higher nocturnal rain accumulations will
occur within a relatively thicker 8k to 9k ft moistened layer
underneath a thick slab of dry air aloft.

A weakness will develop within the upper ridge over the islands
Monday. An upper trough and associated cold front will approach
the island chain from the northwest and merge with the weakness
channel over the state going into Tuesday. It is a bit early to
determine the evolution of this trough but it will more than
likely pull up moist equatorial air northward over the islands
while destabilizing the regional atmosphere. Numerical weather
prediction guidance has precipitable water (pwat) values nearing
the upper 90 percentile for this time of year being pulled up and
over the islands from Monday through Thursday. 500 mb temperatures
within the trough or upper low should be cold enough (-10 to -12
C) destabilize the regional atmosphere enough to result in
isolated thunderstorms Tuesday roughly centered between the Kauai
and Alenuihaha Channels. The bulk of the higher pwat air is
currently being modeled to be in the vicinity of Big Island and
points east while the greatest instability exists west over the
central and western islands. While the greatest moisture and
highest instability may be slightly out of phase, confidence is
mounting that the highest threat from thunder will anchor in the
proximity of Oahu and Maui County while the highest rainfall that
could lead to flooding will focus on Big Island. Another element
that increases confidence of this potentially impactful, active
mid week pattern is the upper divergence forming along the eastern
flank of the upper trough...opening up across the island chain.
This upper forcing within a very moist air mass and destabilizing
cooler mid to upper levels should provide the necessary ingredients
to prolong a very wet pattern through Thursday. A drier late week
as upper ridging begins to take hold. Re-established surface high
pressure to the northeast will reintroduce strengthened trade
winds Thursday and Friday. An upper trough and assoicated surface
front will approach the state next weekend. This trough may pack
enough of a punch to actually push our first cold front across the
island chain early next week.

Freezing levels falling to around 12k feet, along with the potential
of a saturated column between the -10 and -20 C levels going into
Tuesday, implies that a frozen mix or snow showers will occur
within freezing surface temperatures atop Big Island summits. Mid
level southwesterly winds will also strengthen east of the upper
trough axis and this will significantly increase Haleakala and Big
Island summit winds. Thus, there is increasing chances for both a
Wind Advisory and Winter Weather Advisory for Mauna Kea and Mauna
Loa`s summits Tuesday and Wednesday.

&&

.AVIATION...
Primarily VFR across all local terminals. Possible brief MVFR cats
in both ceilings and visibilities may occur during times of more
moderate intensity showers over such windward-exposed air fields as
HTO and LIH. Weaker trades suggest that local breezes will become
more dominant across wind-sheltered air fields. Brief -SHRA will
continue to mainly focus along windward exposures.

No AIRMETs are in effect.

&&

.MARINE...
Trade wind speeds will decrease today and veer from a more E to
SE direction from Monday to Tuesday as the high pressure ridge
north of the Hawaiian Islands weakens and drifts E in response to
a surface trough over the islands and an approaching cold front
far NW of the state. Additionally, the cold front may advance
into the offshore waters by Tuesday afternoon, bringing locally
strong ENE winds behind it before the front diminishes over the NW
coastal waters Wednesday. Expect Small Craft Advisories to be issued
for most of the Hawaiian coastal waters from Wednesday into
Friday due to a combination of strengthening winds and rising
seas. Isolated thunderstorms are possible over the Hawaiian
waters through much of this week.

Expect multiple overlapping NW swells this week. This will keep
surf heights boosted along exposed N and W facing shores. The
challenge with this pattern will be in tracking the multiple swell
energies from similar directions and similar periods. Wave height
model guidance has trended towards combining these different
swells for the Monday through Friday time period. Decreased the NW
swell heights from model output by a few feet to account for this
discrepancy.

Surf along N facing shores remains small today as a small medium
period NW (310-320 degree) swell slowly declines into Monday. The
next moderate, medium to long period NNW (320-340 degree) swell
will then arrive late Tuesday, peaking Wednesday near High Surf
Advisory thresholds along exposed N and W facing shores, then
declining through the end of the week. Another overlapping small,
medium period NNE (010-020 degree) swell arrives from Thursday
into Friday. Then another small, long period NW (320-330 degree)
swell arrives in Hawaiian waters by Thursday night, peaking late
Friday, then slowly diminishing into next weekend.

Surf along E facing shores will decline into Monday due to the
weakening of the local and upstream trade winds. As the high
pressure ridge moves east later this week, the combination of a
long easterly fetch of 15 to 20 kt winds upstream of the islands
from Tuesday through Thursday, along with strengthening local winds
along the cold front, will produce moderate and choppy surf along
E shores. For S shores, periods of tiny background south swell
energy will linger.


&&

.FIRE WEATHER...
Recent island wide rain and more overcast skies, along with relatively
higher minimum afternoon humidities under light winds, will assist
in maintaining a lower fire weather threat. There is a moderately
high chance for a return to a wet weather pattern from Monday night
onward. This morning`s inversion heights range from 6 to 8k feet.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$


DISCUSSION...Blood
AVIATION...Blood
MARINE...Bohlin
FIRE WEATHER...Blood