Hilo, Hawaii 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

195
FXHW60 PHFO 161400
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
400 AM HST Tue Dec 16 2025

.SYNOPSIS...
An approaching cold front from the northwest will weaken into a
trough as it reaches the far west nearshore waters this evening.
This dying front will merge with what is left of an old
convergence boundary. The bonding of these two features will
provide better focus for redeveloping and lingering mid to late
week rain episodes and isolated thunderstorms that will primarily
impact Niihau, Kauai and Oahu. High pressure will begin to take
hold over the state at all levels this weekend and translate to a
drier pattern heading into the holiday week. Trades will return
over the weekend and significantly strengthen to breezy to locally
strong magnitudes early next week.


&&

.DISCUSSION...
The remnants of a trough, now a lower level convergent zone over
the western half of the state, that provided a pathway for more
moisture-rich southerly air to move in and assist in producing
subsequent Kauai and Oahu rain the past couple of days, is giving
way to a surface ridge axis from the northeast. Kauai and Niihau
picked up another few tenths to nearly two inches of precipitation
overnight with Oahu`s upper terrain capturing a few tenths of an
inch of rain from quick hitting showers traveling up within the
southerly flow. Today will be a similar day for both Honolulu and
Kauai Counties compared to Monday`s rain behavior with occasional
showers putting down an additional few hundredths to a tenth or an
inch along their northern route. The next rain maker will be from
a weakening front moving in from the northwest today and stalling
in the vicinity of Kauai County later this afternoon into evening.

There will not be much upper level support to push tonight into
Wednesday morning`s boundary eastward. As the associated upper
lower low near 27N170W ejects northeastward up and over upper
ridging anchored over the eastern Pacific it will take much of
the energy that will be required to push the low level boundary
eastward. Shortwave energy passing around the base of the trough
Wednesday may be the impetus to advancing the trough/convergence
zone further east toward Oahu. Thus, confidence is low that that
this latest trough will make it much past Kauai. As was the case
the past couple of days, the stretched lower to middle level
frontal zone will provide a channel for higher moisture to ride
up from more southern latitudes. The southern branch of the polar
jet nosing in  from the west at mid week may provide enough
downstream difluence, along with any shortwave riding up from the
southwest, to trigger periods of numerous showers and that rouge
thunderstorm. Since most of the island chain will be shrouded with
mid to high level clouds the next few days, the lack of sun will
cross off any convective surface initiation. Future rain
production will be from upper level forcing within an ongoing
moisture rich air mass residing over the state. Periodic oceanic
clustering rain cells may become organized enough to quickly lay
down 1 to 2 inches. This may create mid week nuisance flooding and
the ponding of water within low lying areas over the western
islands of Oahu and Kauai. Maui and Hawaii Counties will also
receive rain but it will be much more limited as showers will be
surface-based convection from lift created by the local diurnal
breezes.

Showers will linger on through Friday but a drier trend will
commence around Friday when the lower level southerly flow begins
to back more easterly. Trades attempt a comeback Friday but will
be in full force by Saturday. Upper ridging will form over the
islands and this subsidence will kick off several days of typical
trade weather in the days leading up to Christmas. Model guidance
is suggesting that a large and in charge North Pacific surface
high (around 1045 mb) will press down a tight enough pressure
gradient to significantly strengthen trades this time next week.
If this scenario comes to fruition, expect moderate to locally
strong-in-gust easterlies from Monday through Wednesday.


&&

.AVIATION...
A surface trough will linger northwest of Kauai enhancing showers
and producing isolated thunderstorms along the trough axis.
Southerly winds across the state will produce unsettled weather
conditions with brief MVFR conditions in low clouds and showers
across the islands of Kauai, Oahu, Molokai, and Lanai today. The
eastern islands of Maui and the Big Island will remain more stable
with prevailing VFR conditions for most airfields. Southerly
winds may bring daytime wind gusts in the 20 to 25 kt range over
northern slopes of island mountains.

AIRMET Sierra remains in effect for tempo mountain obscurations
for Oahu, Molokai and Lanai this morning. These low cloud ceilings
should improve by the afternoon hours.

AIRMET Tango for tempo moderate turbulence aloft FL240 to FL340
above Kauai and Oahu associated with the subtropical jet stream
over the islands.



&&

.MARINE...
Weak surface trough is near Kauai and another cold front is
immediately west of the islands this morning. This front maintains
a chance for isolated thunderstorms over the western nearshore
waters through at least Wednesday. Locally fresh S to SW winds
emerge in the meantime as the low digs south of 30N. Winds then
weaken late this week followed by returning trades perhaps as
early as Sunday.

A long period N swell has peaked overnight and will continue to
drop through today. The High Surf Advisory (HSA) will be allowed
to expire at 6am. The Small Craft Advisory will also expire at 6am
as seas drop below criteria. Renewed energy out of the NW
quadrant (300-320) will elevate surf near the HSA threshold once
again early Wednesday through Thursday.

E shores remain flat except where long period NW-N swell energy
wraps. S shores experience short period wind wave chop and S
fresh swell energy due to persistent S-SW winds through the week.


&&

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

&&

$$


DISCUSSION...Blood
AVIATION...Bohlin
MARINE...Walsh