856
FXHW60 PHFO 180127
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
327 PM HST Mon Nov 17 2025

.SYNOPSIS...
An upper level low southwest of the islands will pull moisture
over the eastern half of the state through Tuesday. This feature,
along with a developing surface trough, will bring an increased
chance of heavier showers Tuesday night through Wednesday,
especially for windward portions of Maui and the Big Island.
The chance of heavy rainfall diminishes late Wednesday into
Thursday, though breezy showery trades will persist. A brief
period of stable and drier trade wind conditions is expected on
Friday, followed by more showery weather into the weekend as a
cold front advances toward the island chain.


&&

.DISCUSSION...
Latest water vapor imagery depicts an upper level low centered
several hundred miles south southwest of the state with an associated
cyclonic spin aloft over the island chain. Enhanced mid and upper
level moisture, driven by the low, can be seen streaming in from
the southwest over Maui County and the Big Island. Near the
surface, moderate easterly trades continue to push typical light
to moderate showers against windward and mauka areas. This pattern
is expected to hold into the early evening.

By late evening and into tonight, the mid and upper level cloud
shield is progged to thicken, especially over the eastern portion
of the state. Hi- res model guidance, such as the WRFARW and FV3,
show stratiform precipitation developing over the summits first,
then possibly spreading to lower elevations as the dry air below
slowly beings to moisten. Freezing levels near 13Kft or 14Kft,
along relatively dry air in place nearly the surface, should
support a wintry mix of rain and snow at summits of the Mauna Loa
and Mauna Kea on the Big Island. Thus, have opted to issue a
Winter Weather Advisory from 6 PM HST this evening through the day
Tuesday.

By Tuesday, both the GFS and ECMWF begin to deepen an upper level
trough northwest of the state as a surface trough develops south
of the Big Island. As conditions become more unstable aloft,
both models indicate an area of rather heavy rainfall developing
south of the Big Island, in association with the aforementioned
surface trough. However, uncertainly remains an issue. The GFS is
still much more robust with the intensity than the ECWMF, though
it has been trending slightly weaker with the latest 18Z run. This
pocket of deep moisture should lift northward late Tuesday into
Wednesday, causing conditions to deteriorate for windward
portions of the Big Island and Maui. Strong trades, combined with
deep moisture and some instability aloft, may lead to a periods
of heavy rainfall for these areas and a Flood Watch may be needed
late Tuesday night through Wednesday. If current trends hold,
however, flooding will be limited to mainly the nuisance variety
and the Watch wouldn`t be necessary. Forecast rainfall totals
currently range from under an inch with the ECMWF`s weaker forcing
to one to two inches from the GFS. For all other islands Tuesday
night through Wednesday, the inversion height should deepen to
near 15000 feet. Surface high pressure building far north of the
state will bring gradient driven strong trades with scattered to
numerous showers that will affect both windward and leeward sides
of the islands. The flooding threat remains low over the smaller
islands due to the speedy nature of the showers and lack of any
substantial forcing.

Any threat for heavy rainfall will decrease late Wednesday, but
breezy and wet conditions are expected into Thursday. The strong
surface high passing to the north will maintain breezy trade
winds, and even though precipitable water will be decreasing, the
GFS and ECMWF keep abundant moisture around the islands,
suggesting a rather wet pattern.

A brief period of stable and drier trade wind conditions is
expected on Friday, followed by more showery weather into the
weekend as a cold front approaches the island chain.


&&

.AVIATION...

Moderate east southeast winds will gradually weaken overnight,
with land breezes possible across the western end of the state.
In this flow, isolated to scattered showers will move into
windward areas, with some weak surface convergence boundaries
downstream of island terrain bringing a few showers to leeward
areas at times. VFR conditions will generally prevail, with brief
MVFR possible in showers.

On Tuesday, winds will strengthen and back out of the east
northeast, focusing low clouds and showers over windward areas.
However, winds will remain lighter and veered east-southeast
across the eastern end of the state. As deeper moisture streams up
from the southeast, showers will increase in coverage beginning
early Tuesday morning. MVFR, or even IFR, conditions will be
possible in heavier showers.

AIRMET Sierra is in effect for mountain obscuration for windward
portions of Maui and the Big Island this afternoon. This AIRMET
will likely be needed for portions of the island chain through at
least Tuesday.

AIRMET Tango is in effect for moderate turbulence in the mid to
upper levels. This AIRMET will likely be needed through at least
Tuesday morning.

AIRMET Zulu is in effect for some light icing due to the influx
of high clouds and will likely be needed into Tuesday morning.


&&

.MARINE...

A front approaching the state from the far northwest will weaken
the ridge and veer moderate to locally fresh easterly trade winds
more to a east southeast direction to more gentle to moderate
speeds the tonight into Tuesday. The front will weaken as it
enters the northwest offshore waters Tuesday, then lift to the
north Tuesday night into Wednesday. Near gale- force winds are
possible behind the front in the offshore waters. An upper level
trough and deep moisture surging from the south could produce thunderstorms
over the offshore waters. The confidence of thunderstorms over the
coastal waters has decreased thus have removed them from the
forecast at this time but will continue to monitor.

Behind the front, a new high building north of the islands will
help trades strengthen across the state to fresh to locally near
gale speeds. Combined with incoming northwesterly swells, expect
winds and seas to exceed Small Craft Advisory thresholds for
exposed coastal waters Wednesday into Thursday.

A small, short period NE and small, medium period NW swell will
continue to slowly decline into Tuesday. Overlapping NW to NNW swells
rest of this week will keep surf heights boosted along exposed N
and W facing shores. A pair of small to moderate, long period NNW
(310-340 degree) swells will arrive Tuesday, peaking Wednesday.
Surf could peak near or above High Surf Advisory (HSA) thresholds
along exposed N and W facing shores before gradually declining
Wednesday night through the end of the week. Another overlapping
small, short to medium period N (350-010 degree) swell arrives
from Thursday into Friday. Then another moderate, long period NW
(310-330 degree) swell arrives Friday, peaking near HSA
thresholds over the weekend.

Surf along E facing shores will continue to decline tonight into
Tuesday due to the weakening of the local and upstream trade
winds. As a new high pressure builds N of the state Wednesday
through Thursday, rough and choppy surf along E shores could near
HSA levels. For S shores, periods of tiny background south swell
energy will continue to move through keeping surf from going flat.


&&

.FIRE WEATHER...

Moderate trades and higher humidity will maintain conditions below
critical fire weather thresholds. Wet conditions are expected
Tuesday into Thursday, with heavy rainfall possible over recent
burn areas on the Big Island.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 PM HST Tuesday for Big Island
Summits.


&&

$$


DISCUSSION...Thomas/JVC
AVIATION...Farris
MARINE...Almanza
FIRE WEATHER...Thomas/JVC