019
FXHW60 PHFO 070114
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
314 PM HST Tue Oct 6 2026

.SYNOPSIS...
Weakening trade winds will produce light rainfall over mainly
windward areas tonight. Low pressure will develop north of the
state on Wednesday, causing winds to shift out of the south and
allowing sea breezes to produce a few interior showers in the
afternoon. Deep southerly winds will draw tropical moisture over
the portions of the island chain Wednesday night through at least
Thursday, bringing some potential for flooding rainfall. The low
will weaken several hundred miles northwest of Kauai Friday and
Saturday then lift away on Sunday, though a few heavy showers may
linger through the weekend under light winds. Light trade winds
are expected to return early next week.

&&

.DISCUSSION...
Stable and somewhat dry trade winds continue to slowly weaken
this afternoon as a cold front 800 miles northwest of Kauai pushes
a surface high eastward. A slowly eroding mid level ridge over
the islands is maintaining stable conditions, and rainfall has
been modest and focused over windward areas.

Winds will weaken considerably tonight and begin to shift out of
the east to east-southeast as surface low pressure develops along
the stalling front roughly 800 to 900 miles north of Kauai. No
significant rainfall is expected, and land breezes could push most
showers offshore in the predawn hours.

The low will intensify and drift to about 700 miles north of
Kauai on Wednesday. Since this feature will be somewhat far away
from the islands, local winds will shift out of the southeast to
south but are only expected to be at gentle to moderate strength.
As a result, expect afternoon sea breezes to overpower the
background flow along north shores and generate isolated interior
showers in the afternoon. Stability will decreasing, though heavy
showers are not expected at this time.

A humid southerly flow will bring increased chances for widespread
rainfall Wednesday night through at least Thursday. The low be at
its strongest and closest to the islands at this time, possibly
within 600 miles north of Kauai. Moderate southerly flow will
draw up an area of deep tropical moisture over the islands while
a jet stream entrance region along the eastern flank of the low
provides some moist ascent. This could lead to a period moderate
to locally heavy rainfall favoring the western half of the island
chain but possibly extending as far east as Maui. Due to the
southerly flow, leeward areas, which tend have a lower threshold
for flooding, could be exposed to potentially heavy rainfall. High
resolution guidance yet to produce a concise picture of a flood
threat, though the highest chances would be late Wednesday night
and early Thursday. We have held off on issuing a Flood Watch
until we see better model agreement. While gusty downsloping
winds are typically a concern in this setup, the flow does not
appear to be strong enough for winds to reach advisory levels.

The low will stall and begin to gradually weaken roughly 700
miles northwest of Kauai on Friday. The jet stream on its eastern
flank will retreat north of the islands. This will reduce upper
level support for widespread heavy rainfall. However, light
southerly winds will persist, with daytime sea breezes supporting
spotty afternoon showers and dew points hovering in the low to
mid 70s.

The humid flow will gradually shift out of the southeast on
Saturday. The GFS and ECMWF suggest that the highest rainfall
chances will be along a weak surface convergence zone near Oahu
and Kauai, and ridging aloft will build in from the east and
provide increased stability for at least Big Island. The low is
expected to fill as it lifts off to the northeast Sunday. Aside
from the possibility of variable winds on Kauai, conditions should
be similar to Saturday.

Light trade winds are favored to return Monday.

&&

.AVIATION...
Weak trade wind pattern will give way to an increasing chance of
rain by Thursday (see main forecast discussion for more details).
Winds will weaken and veer southerly by Wednesday. Scattered
showers may increase Wednesday night, especially over mountain
areas, with periods of MVFR ceilings and visibility possible.

No AIRMETs are currently in effect. Localized mountain
obscuration will be possible later this afternoon and tonight as
moisture and cloud cover increase, but widespread conditions are
not expected at this time.

&&

.MARINE...
Winds will veer to the east southeast this afternoon and tonight
as a low pressure system and an associated cold front develops
north of the state and approaches from the northwest. A trough
extending from this low is forecast to move into the northwest
offshore waters by Wednesday afternoon. The low will stall north
of the islands and draw moisture out of the tropics and over the
area through the second half of the week, so expect an increase in
showers with moderate south to southeast winds. Thunderstorms
will be possible over the waters around Kauai and Oahu, mainly
Wednesday night into Thursday morning. The trough could
potentially linger into the weekend as it dissipates.

Long period south swell energy will continue filling in today,
keeping surf elevated but just below advisory levels this
afternoon. By Wednesday, this swell will begin to fade, but surf
heights will change little this week, as a mix of new, small
south swells will keep surf elevated near or just above seasonal
norms. Another long period swell then looks to fill in this
weekend, bumping surf back up to just below advisory levels.

A long-period northwest swell will continue building today,
pushing surf for north-facing shores up tonight to near moderate
levels on Wednesday. Small to moderate surf is then forecast
through the rest of the week even as swell energy becomes shorter
period, since it will be reinforced by a low to the north-
northwest of the Hawaiian Islands. A larger moderate swell could
arrive early next week, bringing north shore surf to just below
advisory thresholds. Surf along east facing shores will remain
small as local winds remain fairly weak.

A small, long-period west swell originating from Typhoon Choi-
wan is forecast to reach the islands Thursday into the weekend,
which may produce moderate surf for west-facing shores.

&&

.FIRE WEATHER...
Gentle to moderate breezy trades will continue a slow decline
tonight, with humidity just above the critical threshold this
afternoon. Fire weather risk diminishes through Friday as
southerly winds bring increased moisture and humidity. The
inversion range from 6 kft to 8 kft through the evening and
will deteriorate Wednesday.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Wroe
AVIATION...PECHACEK
MARINE...Tsamous
FIRE WEATHER...Wroe

NWS HFO Office Area Forecast Discussion