Ewa Gentry, Hawaii 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

622
FXHW60 PHFO 150203
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
403 PM HST Tue Oct 14 2025

.SYNOPSIS...
Trade winds will strengthen to become moderate to locally breezy
this week. The main focus for this week is on the increasing
shower trends and the potential for isolated thunderstorms as an
unstable upper low approaches the islands from the north and bands
of deep moisture filter across on the trades. Late this weekend
into early next week, conditions should improve as the upper low
lifts away from the state.

&&

.DISCUSSION...
This afternoon, satellite and radar show a typical trade wind
pattern with limited clouds and showers moving into windward and
mauka areas of the smaller islands and more extensive cloud cover
over the Big Island. In addition, an upper level low can be
clearly identified in the water vapor satellite imagery, located
about 350 miles to the northwest of Kauai.

Trade winds will continue to build back over the state through
the week as the surface trough northwest of the state dampens out
and high pressure to the distant northeast builds. Generally light
to moderate easterly trades are expected through this evening,
then as the high builds and tightens the local pressure gradient,
they`ll strengthen to become moderate to locally breezy for the
rest of the week.

The focus for this week`s forecast remains on the increasing
shower trends as the upper low approaches the islands from the
north. This feature will bring instability aloft, and batches of
moisture will be transported across the area in the trade wind
flow, increasing the potential for enhanced trade wind showers
and isolated thunderstorms. The first band of moisture (remnant
moisture from an old front) is expected to arrive Wednesday night,
with models showing precipitable water values (PWats) increasing
to 1.6-1.8 inches. This band will be quickly followed by a second
on Thursday night into Friday. While the low level moisture and
instability aloft are notable, the surface "lifting mechanism" to
force that moist air to tap into the instability aloft looks weak.
Orographic lift as the trades interact with island terrain will
likely focus the bulk of the heavier shower activity over windward
and mauka areas through the period, though weak surface
convergence bands may also provide an additional source of lift.
Additional batches of moisture will filter through on the trades
while the low lingers over the western end of the state through
the weekend, prolonging the potential for enhanced trade wind
showers and isolated thunderstorms.

Storm total rainfall estimates for this multi-day event may
exceed 2 inches in terrain favored locations. It remains too
early to pin down any islands for flooding, however a Flood Watch
may be needed at some point as this event unfolds. Any flooding
potential may tend to favor the western half of the state, as will
the thunderstorm potential, as these islands will be closer to
the unstable upper low center. The Big Island may also see
isolated thunderstorms from late Thursday morning to early evening
as the low level convergent band drifts through the island.

Sunday into early next week, global model guidance begins to
diverge, but it looks like mid level ridging will try to briefly
build in from the southeast and establish a more stable trade wind
weather regime. Light showers will focus over windward and mauka
areas, particularly during the overnight and early morning hours.
Then long range weather models are hinting at yet another
unstable upper low drifting towards the Hawaiian Islands early to
midweek next week, potentially triggering yet another round of
wet weather across the island chain. Stay tuned.

&&

.AVIATION...
Moderate easterly trade winds will strengthen to moderate to
locally gusty levels tonight into Wednesday. An upper level low
will sag south over the western end of the island chain,
increasing shower trends by early Wednesday morning. Brief periods
of MVFR conditions are possible in passing showers mainly over
windward and mountain areas overnight and early morning hours. Iso
IFR conditions are possible in heavier showers.

AIRMET has been issued for moderate turbulence below FL250...but
turbulence will be most likely at the lower levels farther south
near the Big Island and at the upper portion of the range farther
north near Kauai.

&&

.MARINE...
Light to moderate trades become moderate to fresh by Wednesday as
weak surface troughing over the western end of the state advances
west and dissipates. The Small Craft Advisory (SCA) for elevated
seas will be allowed to expire this afternoon while the SCA for
winds around Maui County and the Big Island remains in effect. An
approaching upper low brings a chance for thunderstorms to area
waters tonight into the weekend.

Moderate to long period NW (310-320) swell brought an early
morning peak to N and W facing shores as indicated by the PacIOOS
Buoy at Waimea Bay where observations hovered near the High Surf
Advisory (HSA) threshold for much of the day. During the last few
hours, energy has begun to consolidate in the lower energy bands
even as the observed significant wave height remains rather
steady. As such, the HSA will also be expired this afternoon.

Small, medium period S swell continues through the week with
minor longer period pulses arriving tonight and Saturday. E shores
remain small through the near term, but will see increasing short
period action as trades strengthen mid-week.

&&

.FIRE WEATHER...
Wind speeds and afternoon minimum humidity levels will likely
remain below critical fire weather thresholds this week. Unstable
conditions will produce increasing wet weather trends across the
state from Wednesday through Saturday. Locally heavy rain and
thunderstorms are possible during this time period. Temperature
inversion heights near Maui and the Big Island will range from the
6,000 to 7,000 feet elevation range this evening.

&&

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


&&

$$


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