717
FXHW60 PHFO 221357
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
357 AM HST Sat Aug 22 2026

.SYNOPSIS...
Trade winds will continue to strengthen today as Tropical Storm
Moke moves from east to west, south of the islands. This system
will deliver periods of rainfall to all islands from late tonight
through Monday, but heaviest along windward and southeast slopes
of the Big Island. A Flood Watch remains in effect for the Big
Island. Typical drier trade wind weather will return by mid next
week.

&&

.DISCUSSION...
Latest IR satellite imagery loop continues to show deep convection
several hundred miles southeast of the Big Island, in association
with Tropical Storm Moke. The center of Tropical Storm Moke was
located roughly 500 miles southeast of Hilo and moving at around
12 mph to the west northwest. Closer to home, mainly clear skies
prevail with few low clouds pushing against the island`s windward
slopes. The 06Z Hilo sounding shows a fairly shallow subsidence
inversion height near 5000 feet with relatively dry air both above
and below the inversion. Thus, it comes as no surprise that the
radar has been quiet with only isolated light showers dotted
over the region. Trade winds have begun to slowly ramp up
statewide the last several hours into a more moderate range,
generally 10 to 20 mph, with gusts to around 30 mph at wind prone
sites.

Local pressure gradients will further tighten today as Hawaii
becomes sandwiched between the low pressure of Tropical Storm Moke
(as it moves west, south of the islands) and a 1026 mb surface
high far to the northeast of the region. Winds across select zones
of Maui County and the Big Island, mainly the typical tradewind
prone zones in the lee of mountains or passes, should reach
advisory level by this afternoon. A Wind Advisory has been issued
for these areas and has a starting time of noon. Hi-resolution
model guidance indicates nearing High Wind Warning levels in the
lee of the Kohala mountains on Big Island later this evening into
tonight. If this comes to fruition, and winds increase above
guidance, the advisory for this zone would need to be upgraded.
Leeward Ko`olau mountains and Wai`anae mountain zones on Oahu may
be added to the advisory on a later shift as winds near criteria
this evening into tonight. Trade winds remain strong through
Sunday, then begin to dwindle late Sunday into Monday morning.

By this evening, a slug of deeper low level moisture from
Tropical Storm Moke begins to approach the Big Island from the
east. Showers will become numerous along windward and southeastern
sections of the Big Island late tonight through Monday with
periods of embedded heavy rain. Both the GFS and ECMWF share
similar solutions and the NHC track forecast for Moke has changed
very little during the past several advisories. For this reason,
forecast rain amounts were held steady overnight with no major
changes. A Flood Watch for the Big Island will go into effect
tonight and continue through Monday afternoon. Rainfall totals of
5 to 10 inches, locally up to 15 inches are possible over the
windward and southeast slopes of the Big Island. It will not take
a significant amount of rain to cause flash flooding due to
saturated grounds from recent heavy rain. For the remaining
islands, showers will also become more numerous as deeper low
level moisture increases from Tropical Storm Moke. However, totals
should be much less with only up to a few inches of rainfall
accumulation expected. Isolated amounts up to 4 inches are
possible over the eastern portion of Maui as moist easterly flow
moves up the slope of Haleakala.

Early next week, as Tropical Storm Moke pushes further west, away
from the islands, both the GFS and ECMWF indicate some residual
moisture and instability left behind in its wake. This could spell
more weather weather for the area, especially over the higher
terrain of Maui and the Big Island. Details will be worked out in
the coming days. By Wednesday, a surface high northeast will once
again dominate and bring a return of more typical trade wind
weather.


&&

.AVIATION...
Trade winds will fill back in over the islands as Tropical Storm
Moke approaches and passes south of the Big Island this weekend,
increasing the pressure gradient across the state. Trades will
gradually strengthening from east to west, becoming strong by this
afternoon and continuing to build on Sunday. AIRMET Tango will
likely be needed for low level turbulence downwind of island
terrain.

While occasional pockets of MVFR conditions will be possible
within passing showers along windward and mauka locations today,
VFR conditions are expected to prevail. Tonight into Sunday,
increasing moisture over the eastern end of the state as Tropical
Storm Moke passes by to our south will result in increasing
chances for heavy rainfall, along with low visibilities and
ceilings, across the Big Island. This will bring more widespread
MVFR and IFR conditions.


&&

.MARINE...
Trade winds will begin to strengthen across the coastal waters
in response to Tropical Storm Moke passing south of the islands
this weekend. A Small Craft Advisory (SCA) has been issued through
this afternoon for the eastern two thirds of the coastal waters.
The SCA has been expanded to include all nearshore waters from
tonight through Sunday afternoon. Stronger winds and Moke
generated wind wave swell may push significant seas to near 10
feet within Big Island`s eastern waters this weekend.

A Tropical Storm Warning is in effect for the offshore waters as
the passage of Tropical Storm Moke introduces tropical storm
force conditions to these waters from tonight through Sunday.

East-facing shore surf will gradually build this weekend in response
to strengthening trades. Surf along east and south-facing shores will
be impacted by a short period east southeast swell generated by
Tropical Storm Moke as well as northeast wind wave swell as a result
of the stronger trades. As Moke passes by to the south this
weekend, a mounting southeast swell will veer and become south to
southwest into Monday. This small, short period captured easterly
fetch from TS Moke may push Big Island east surf to advisory
levels tonight into Sunday. Moke`s wind field is forecast to be
relatively small and, with potential minor deviations in forecast
track, confidence for Big Island east-facing shore advisory surf
remains low.

Surf along most south-facing shores will be slightly below summer
norms but still remain somewhat elevated due to a lingering small,
long period south southwest swell through the weekend. Another
reinforcing small south swell is expected over the weekend which will
hold these near summertime heights. A series of south swells next week
on top of this resident swell may potentially increase south surf to
near advisory levels.

Small, medium to long period west to north swell originating from
Hurricane Lala will arrive along north and west-facing coasts this
weekend.


&&

.FIRE WEATHER...
Trade winds continue to increase today and the inversion,
currently around 5-6 kft, will steadily weaken and eventually
erode altogether as deep moisture associated with TS Moke moves
into the area tonight into Sunday. Heavy rain is expected over
windward and SE facing slopes of the Big Island on Sunday.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from noon today to 6 PM HST Sunday for Lanai Mauka-
Kahoolawe-Maui Leeward West-Kohala-Big Island Interior-Molokai
Southeast-Molokai North-Molokai West-Molokai Leeward South-Lanai
Windward-Lanai Leeward-Maui Central Valley North-Maui Central
Valley South-Windward Haleakala-South Haleakala-Big Island South-
Big Island Southeast-Big Island North.

Flood Watch from late tonight through Monday afternoon for Big
Island-

Small Craft Advisory from 6 PM this evening to 6 PM HST Sunday
for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward
Waters-Kauai Channel.

Small Craft Advisory until 6 PM HST Sunday for Oahu Windward
Waters-Oahu Leeward Waters-Kaiwi Channel-Maui County Windward
Waters-Maui County Leeward Waters-Maalaea Bay-Pailolo Channel-
Alenuihaha Channel-Big Island Windward Waters-Big Island Leeward
Waters-Big Island Southeast Waters.


&&

$$


DISCUSSION...Thomas
AVIATION...Vaughan
MARINE...Blood
FIRE WEATHER...Thomas