243
FXHW60 PHFO 280609
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
809 PM HST Tue Oct 27 2026

.SYNOPSIS...

A trough moving over the island chain from the west will bring
clouds and showers to the state through tomorrow night. An
accompanying upper level disturbance provides the instability for
the chance for thunderstorms and locally heavy rainfall.
Conditions are expected to improve Thursday or Friday, with trade
winds returning this weekend.

&&

.SHORT TERM UPDATE...

Showers continue moving over the state. While most showers are
currently on the lighter side expect that to change within the
next few hours. A heavier pocket of showers with some embedded
thunderstorms is southwest of Oahu and moving to the northeast.
Rainfall will continue to increase and may be heavy at times
especially in any thunderstorms. No changes were made to the
previous forecast as everything is on track.

&&

.PREV DISCUSSION...
Issued at 323 PM HST Tue Oct 27 2026

No major changes to the forecast with the afternoon package. The
High Wind Warning for the Big Island summits continues, as winds
have reached advisory levels late this afternoon and are expected
to continue to increase tonight. There were some minor tweaks made
to the PoPs and associated fields for the first part of tonight as
the rain is not spreading across the islands as quickly as we
anticipated this morning.

While clouds have been plentiful over the islands today, rainfall
totals have been light. Radar this afternoon shows heavier
rainfall moving over the Kauai Channel, with light rain moving
over the leeward and south portions of Oahu, Molokai and Lanai.
Expecting the moderate to heavier shower activity to spread
across the islands in the next few hours.

Satellite derived precipitable water (PW) continues to show over
3 inches about 325 miles southwest of the islands. This is twice
the normal PW for this time of year. The 2 inch satellite derived
PW is approaching the islands of Maui County this afternoon. The
afternoon sounding from Hilo have 2.30 inches of PW and Lihue had
1.76, both about the normal value around 1.5 inches.

The remnants of Olana are more than 1300 miles southwest of the
islands, with a monsoon trough extending nearly 800 miles to the
east-northeast of the remnants, and trough extending to the east
and then northeast of that. The trough remains south of the
islands, with some surface lows forming along the trough. The low
of most concern was analyzed about 530 miles southwest of Oahu
this afternoon. The GFS and ECMWF models forecast the low to be a
little further north at this time, but both agree with a weak low
moving towards the islands. Satellite shows a broad area of
layered clouds with embedded thunderstorms near the low and in the
area between the low and the main Hawaiian islands. This area
corresponds with the elevated PW mentioned above.

A north-northeast to south-southwest oriented upper level trough
is about 800 miles northwest of Kauai, and is expected to move to
the east over the next 24 hours, and will help to destabilize the
airmass over the islands as the jet moves over the islands.

The Flood Watch is in effect through tomorrow night. The highest
rainfall totals are expected to be focused over Maui County and
Oahu. However, all islands remain under the Flood Watch with the
potential for thunderstorms and locally heavy rain. Slow moving
cells may become anchored along the terrain of the islands, which
could lead to flash flooding anywhere. Breezy east winds could
form just north of the low, while gusty southerly winds form to
the south. Strong thunderstorms with localized damaging gusty
winds may develop along and just south of the surface trough.

The threat of heavy rainfall will diminish Thursday and Friday.
The jet stream aloft will lift to the north as the upper level
trough moves to the west and an upper level low develops along the
trough. The weak surface trough, with ample moisture will likely
linger, providing some chance for spotty heavy showers that could
require the Flood Watch to be extended.

Friday night into Saturday a brief period of trade winds may
return as the lingering moisture associated with the trough is
pushed south of the islands. The GFS and ECMWF are showing breezy
northeast winds developing Sunday as a shallow front moves near or
over the state.

&&

.AVIATION...

Widespread SHRA continue to push over the central portion of the
state this evening. The timing of the heaviest rain will be early
tonight through much of the overnight hours for the western end
and central portion of the island chain. MVFR/IFR cigs/vis are
expected with the rainfall. TEMPO groups are included in most
locales to account for a period of RA with IFR cigs/vis. There
will likely be isolated instances of RA+. VCTS/TS not included due
to low confidence at this time. By late tonight into early
tomorrow morning, PHTO and PHKO will start to see rain moving in
as the area of precip moves to the east.

Winds will remain generally weak through the forecast period.
However, thunderstorms could bring brief gusty and erratic winds.

AIRMET Sierra for mountain obscuration remains in effect abv 025
for all islands due to the increase in low clouds and steady rain.


&&

.MARINE...
Issued at 323 PM HST Tue Oct 27 2026

A vigorous surface trough and possible elongated area of low
pressure will move over coastal waters surrounding Maui County
and Oahu tonight and Wednesday as a broad surface low meanders
roughly 800 nm northeast of the islands. Expect moderate easterly
winds to develop north of the trough and southeast to south winds
to form south of the trough. Close to the trough, these winds
could become locally strong, especially if a surface low deepens
near the islands, and a Small Craft Advisory (SCA) is in place
for waters around Maui County and Oahu through Wednesday. In
addition, strong thunderstorms along the trough could produce
erratic wind gusts in excess of gale force. The trough and
possible low will weaken near the Big Island Thursday, allowing
ridging to the north to drive moderate to fresh easterly winds
over most waters and southerly winds near Big Island. The trough
will move south of Big Island Friday, and moderate to locally
fresh trades will prevail Friday night and Saturday. Stronger
northeast winds may develop on Sunday and require an SCA.

A moderate northwest swell will decline late tonight and
Wednesday, allowing surf to fall below seasonal average along
north- and exposed west-facing shores. This swell will fade by
Thursday. A small, short-period north-northeast swell will
persist through much of the week, and may even become moderate
Thursday and Friday with the arrival of reinforcing energy from
the northeast. A larger long-period northwest swell will arrive
late Saturday and may push surf above the high surf advisory
threshold Sunday and Monday.

A series of overlapping south-southwest swells will continue
through the weekend. The current swell is producing south shore
surf near seasonal average, and additional pulses on Wednesday
and Friday could produce above average surf.

Surf along most east-facing shores will be small through the
first half of the week, but areas exposed to wrapping north to
north- northeast swells will experience periods of moderate surf.
A moderate northeast swell is possible Thursday and Friday.

&&

.FIRE WEATHER...
Issued at 323 PM HST Tue Oct 27 2026

Deep tropical moisture spreading over the islands is bringing the
threat for heavy rain and thunderstorms at least through
Wednesday night and possibly into Thursday. As a result, fire
weather concerns will be low through the next several days.
Inversion heights have eroded near the Big Island and sit near
7000 feet near Kauai.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flood Watch through late Wednesday night for Big Island East-Big
Island Interior-Big Island North-Big Island South-Big Island
Southeast-Big Island Summits-Central Oahu-East Honolulu-Ewa
Plain-Haleakala Summit-Honolulu Metro-Kahoolawe-Kauai East-Kauai
Mountains-Kauai North-Kauai South-Kauai Southwest-Kipahulu-
Kohala-Kona-Koolau Leeward-Koolau Windward-Lanai Leeward-Lanai
Mauka-Lanai South-Lanai Windward-Maui Central Valley North-Maui
Central Valley South-Maui Leeward West-Maui Windward West-
Molokai Leeward South-Molokai North-Molokai Southeast-Molokai
West-Molokai Windward-Niihau-Oahu North Shore-Olomana-South
Haleakala-South Maui/Upcountry-Waianae Coast-Waianae Mountains-
Windward Haleakala.

High Wind Warning until noon HST Wednesday for Big Island
Summits.

Small Craft Advisory from midnight tonight to 6 PM HST Wednesday
for Kaiwi Channel-Kauai Channel-Maui County Leeward Waters-Maui
County Windward Waters-Oahu Leeward Waters-Oahu Windward Waters-
Pailolo Channel.


&&

$$

UPDATE...Walsh
DISCUSSION...M Ballard
AVIATION...Thomas
MARINE...Wroe
FIRE WEATHER...M Ballard