Captain Cook, Hawaii Weather Forecast Discussion

819
FXHW60 PHFO 121339
AFDHFO
Area Forecast Discussion
National Weather Service Honolulu HI
339 AM HST Fri Sep 12 2025
.SYNOPSIS...
A broad subtropical ridge will linger across the Central Pacific
basin into the middle of next week, producing moderate to locally
breezy trade winds each day. Two wrinkles in the forecast will
increase shower trends through this morning as an easterly wave
passes through Oahu and Kauai. Brief passing showers over windward
and mountain areas will return later this afternoon and last
through Monday evening. Another low level wave in the easterlies
will drift through the islands from Tuesday to Wednesday; increasing
shower trends.
&&
.DISCUSSION...
The infrared satellite imagery shows a weak easterly wave drifting
westward through the island of Kauai this morning. Expect
continued enhanced cloud and shower coverage across the western
islands of Oahu, Kauai and Niihau through the early morning hours.
Drier trends are already returning to the eastern islands with
more stable stratocumulus clouds developing east of the island
chain as the high pressure ridge builds stable subsidence
(downward vertical motions) back into the region. Bands of high
level cirrus clouds, made of ice crystals, will drift over the
islands through Sunday. These high level cirrus clouds will likely
enhance sunrise and sunset colors for all islands.
A typical summer forecast with little changes to our day to day
moderate to locally breezy easterly trade wind weather regime
remains in the forecast through Monday evening. Only brief passing
showers are possible with temperature inversion heights in the
5,000 to 7,000 foot range, favoring windward and mountain areas in
the overnight to early morning hours. Dry trends will continue for
leeward areas that are west of island mountains.
The latest medium range models continue to show another wrinkle
in the force developing by early Tuesday morning, as a wave in
the easterlies drifts  from east to west across the island chain.
Low level forcing from this passing low level trough will push
subsidence inversion heights into the 8,000 to 9,000 foot range,
deepening moisture levels, and increasing cloud and shower trends
from early Tuesday morning near the Big Island and Maui, then
spreading westward to the islands of Oahu and Kauai by Tuesday
night into Wednesday morning. One challenge with this forecast
will be in how far north the trough tracks through the islands. If
the trough passes farther south of the state, then these shower
trends will be more limited for the western half of the state. We
have higher confidence that the eastern Hawaiian Islands will see
enhanced shower activity, especially in the early Tuesday morning
hours.
Long range model solutions are hinting at yet more chances for
enhanced shower trends by the end of next week. Stay tuned.
&&
.AVIATION...
A weak trough moving through Kauai this morning will enhance
clouds and showers over Oahu and Kauai through around 18Z today.
Otherwise moderate to locally breezy trade winds will linger
through the week. Brief passing showers will favor windward and
mountain areas in the overnight to early morning hours. VFR
conditions will prevail outside of showers.
No AIRMETs are in effect. AIRMET Sierra for mountain obscuration
over select windward areas is possible through Saturday.
&&
.MARINE...
High pressure will remain far northeast of the state through this
weekend and allow moderate to locally strong trades to prevail
across the local coastal waters. Thus, a Small Craft Advisory will
remain in place for the typically windy channels and waters of
Maui County and the Big Island through at least Sunday morning.
Winds may weaken slightly late Sunday into early next week, then
strengthen once again by midweek.
A small, medium to long period, south swell will continue to fill
in today and help bump up south shore surf to near or slightly
above September averages. This swell will then slowly decline by
late Saturday into Sunday. Small south swell/surf expected
through the remainder of the forecast period.
Surf along north facing shores will be slightly elevated over the
next several days as a small, moderate period, north northwest
swell holds. Beyond Sunday, however, north shore surf will drop
back into the tiny to small range. East facing shores will see
typical trade wind generated energy throughout the forecast
period.
&&
.FIRE WEATHER...
Humidity levels will remain dry into next week with increasing
humidity and shower trends from Tuesday into Wednesday as a weak
low level trough drifts from east to west across the island chain.
Wind speeds will likely remain below critical fire weather
thresholds for the next seven days. Temperature inversion heights
near the Big Island and Maui today will range from 5,500 to 6,500
feet.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 AM HST Sunday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.
&&
$$
DISCUSSION...Bohlin
AVIATION...Bohlin
MARINE...JT
FIRE WEATHER...Bohlin

NWS HFO Office Area Forecast Discussion