Waimea Canyon State Park Hawaii Weather Forecast Discussion

732
FXHW60 PHFO 151322
AFDHFO
Area Forecast Discussion
National Weather Service Honolulu HI
322 AM HST Wed Oct 15 2025
.SYNOPSIS...
A wet trade wind weather pattern developing over the Hawaiian
Islands will produce increasing rainfall, heavy at times, along
with a few thunderstorms into Saturday. All island areas will see
enhanced shower activity with the highest rainfall amounts
favoring the windward mountain areas. Showers will decrease a bit
this weekend as the upper low drifts westward away from the state.
However, another weak upper low moves in near Kauai and Oahu by
Monday triggering another round of wet trade wind weather
potentially lasting into next week Wednesday.
&&
.DISCUSSION...
This mornings satellite imagery, water vapor channel, clearly
shows two upper lows approaching the islands from the north.
Divergent winds are shown along the southern and eastern flank of
this low pressure system with thunderstorms forming around the
cold core center of the low. In the lower levels, using the
infrared satellite channel, we see long bands of unstable clouds
likely associated with remnants of an old East Pacific cold front
riding into the islands on the trade winds. These cloud bands
produce enhanced showers caused by the instability surrounding
the upper low and the convergent lifting of the trade winds
forcing these unstable clouds orographically up the windward
mountain slopes.
For today we expect to see easterly trade winds into the moderate
to locally breezy range with increasing clouds and showers
as the upper low moves in from the north and low level cloud
bands riding in from the east begin to converge over the island
chain. This mornings subsidence temperature inversion heights, as
measured by upper air balloon soundings at Lihue and Hilo at 2 AM
HST (12Z), have risen to the 7,000 to 8,000 foot level. This
means scattered to numerous showers are likely near island
mountains.
An extended period of wet weather will continue to affect all
islands this week with periods of numerous showers falling across
the state into Saturday. Some of these showers will be locally
heavy at times, and thunderstorms are likely over the western
islands of Niihau, Kauai and Oahu. The Big Island may also see a
few thunderstorms on Thursday. Storm total rainfall estimates for
this entire two to three day event may exceed 2 inches in terrain
favored windward locations. Our confidence in which islands will
see the heaviest showers is currently not high enough to trigger a
flood watch at this time. However, a flood watch may be needed
once we see how this pattern evolves in order to narrow down
potential flooding threats to specific islands in the chain.
Showers will linger over the islands on Saturday, with a brief
decrease in shower activity on Sunday as the upper low drifts
westward moving away from the island chain. However, another weak
upper low moves right in from the north on Monday, setting up in
an almost identical location near Kauai and Oahu. Cold air
surrounding this low and divergence aloft will bring yet another
round of enhanced shower activity to the islands next week, from
Monday into next Wednesday. Stay Tuned.
&&
.AVIATION...
Moderate to locally breezy easterly trade winds are expected with
increasing clouds and showers over the next 12 to 24 hours. An
upper level low will move in from the north and set up over the
western half of the state as a bands of unstable low clouds drift
into the region from the east. The convergence of the upper low
with these unstable convergent low cloud bands will increase
shower activity into Saturday.
Brief periods of MVFR conditions are possible in passing showers
mainly over windward and mountain areas favoring the overnight and
early morning hours. Isolated IFR conditions are possible in
heavier showers.
No AIRMETs currently in effect. AIRMET Sierra will likely be
issued later today for mountain obscurations. AIRMET Tango may be
issued later today for upper level turbulence associated with
stronger winds surrounding the approaching upper low.
&&
.MARINE...
Moderate to fresh trade winds are expected today as a weak
surface troughing over the western end of the state advances west
and dissipates. A Small Craft Advisory (SCA) for winds around Maui
County and the Big Island remains in effect until 6 AM HST
Thursday. An approaching upper low brings a chance for
thunderstorms to area waters from later tonight into the weekend.
A moderate to long period NW (310-320) swell that peaked yesterday
will slowly decline through the rest of the week into the
weekend.
Small, medium period S swell continues through the week with
minor longer period pulses arriving this morning 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 into 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 7,000 to 8,000
feet elevation range today.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 AM HST Thursday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.
&&
$$
DISCUSSION...Bohlin
AVIATION...Bohlin
MARINE...Walsh
FIRE WEATHER...Bohlin

NWS HFO Office Area Forecast Discussion