047
FXHW60 PHFO 140831 AAA
AFDHFO

Area Forecast Discussion...UPDATED
National Weather Service Honolulu HI
1031 PM HST Mon Oct 13 2025

.UPDATE...
The latest offshore and nearshore buoy observations this evening
are showing northwest swell heights at least two feet higher than
wave model predictions. Therefore we issued an update to increase surf
heights for exposed north and west facing shores. The High Surf
Advisory and surf forecast products were also updated. A Small
Craft Advisory was issued this evening for waters exposed to the
increasing northwest swell.

&&

.SYNOPSIS...
An upper-level low north of the state will continue to move south
through midweek, weaken some, and slowly move to the west.
Strengthening high pressure far northeast will bring returning
trade winds to the region starting Wednesday. The upper level low
will enhance trade winds showers, particularly over the western
end of the state.

&&

.PREV DISCUSSION...
There have been some changes to the forecast for the PoPs and
weather starting as early as tomorrow night. Changes to the PoPs
bring them in line with the current National Blend of Models (NBM)
but generally only subtle changes. Some changes have been made to
thunderstorm and heavy rain coverage, in keeping with the latest
guidance.

Light winds with localized land and sea breezes will continue
through tomorrow. As the high pressure far to the north-northeast
sinks southward, the pressure gradient over the islands will
strengthen, which will result in trade winds returning on
Wednesday.

An upper level low developing along the northeast to southwest
oriented upper level trough to the north of the islands will
sink southwards towards the islands over the coming days. This
upper level system is already producing thunderstorms to the
northeast of the islands just outside of the offshore waters.

The main question in the forecast is whether or not all the pieces
will come together at the same time. While the GFS and ECMWF both
agree with the upper level low forming along the upper level
trough and sinking southward towards the islands, there are some
subtle differences in strength and placement particularly during
the second half of the week. Precipitable water values increase,
but do not necessarily correspond with the coldest 500 mb
temperatures as the upper low comes closer to the islands.

Moderate trade winds returning at the surface Wednesday could
disrupt organized thunderstorm development. The forecast includes
the mention of thunderstorms, with locally heavy rainfall
possible, Wednesday afternoon into Friday for Kauai and Oahu, and
expands to portions of Maui County and the Big Island Thursday and
Thursday night. While enough guidance suggests that thunderstorms
and some locally heavy rainfall is possible during this time
frame, confidence is lower with regards the possibility of
rainfall that could cause widespread flooding concerns. Will
continue to monitor future model runs to determine if the
conditions are lining up for that or not.

&&

.AVIATION...
Light easterly trade winds will gradually strengthen tonight into
Tuesday to more moderate levels, first for the eastern half of
the state, then for the western half of the state. Expect low
cigs and a few SHRA across leeward and interior locations as
seabreezes persist through rest of this afternoon then clear
overnight as easterly winds take over. Possible MVFR conditions
along windward and mauka areas early Tuesday morning due to low
cigs and few SHRA but VFR will prevail.

No AIRMETs in effect, and none are expected tonight.

&&

.MARINE...
A trough north of the state will continue to disrupt trades
through Tuesday, supporting light east to southeast winds
prevailing across the coastal waters. This trough is forecast to
fade while high pressure builds far to the northeast beginning
Tuesday night. As this occurs, expect trade winds to build back
into the region through the rest of the week. Meanwhile, a low
aloft will approach and move over the islands beginning around
Tuesday night. This upper low is already producing thunderstorms
near the offshore waters, which will continue through Friday.
As this upper low comes closer to the islands it will destabilize
the atmosphere enough to support isolated thunderstorm chances
across the coastal waters from Tuesday night through Friday.

Latest buoy observations show that a moderate, long period
northwest (320 degree) swell is currently moving through the
islands. This swell is originating from a deep low pressure system
that produced storm force winds in the far NW Pacific during the
second half of last week, then continued to aim gale force winds
at Hawaii through early Sunday as it weakened. Additionally, the
quick-moving remnants of Post-Tropical Cyclone Halong also
produced a closer, very brief fetch aimed at Hawaii from a
slightly more WNW (300 degree) direction late last week. As a
result, the current northwest swell is expected to continue to
trend upward slightly into this evening, peak tonight into early
Tuesday, then begin to decline Tuesday afternoon. A High Surf
Advisory remains in effect for north and west facing shores of
Niihau, Kauai, Oahu, and Molokai, and for north facing shores of
Maui through Tuesday. Surf along north facing shores will drop off
Tuesday night through Friday.

Small, medium period south swell energy will continue through the
week with minor pulses of longer periods arriving tonight and
again on Saturday. East shores will remain small due to light
winds, but should begin to increase beginning Wednesday as trades
strengthen.

&&

.FIRE WEATHER...
Light winds and isolated to scattered showers will help maintain
fire weather below critical thresholds for another day, with inversion
heights ranging from 6,000 to 7,000 feet. Heading into Wednesday,
moderate trade winds will be accompanied by an increase in shower
activity which will continue to keep fire weather concerns below
critical thresholds.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST Tuesday for exposed north and
west facing shores of Niihau, Kauai, Oahu and Molokai; including
north facing shores of Maui.

Small Craft Advisory until 6 PM HST Tuesday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters-Kaiwi Channel-Maui County Windward Waters-
Big Island Windward Waters.

&&

$$

UPDATE...Bohlin/Walsh
PREV DISCUSSION...M Ballard
AVIATION...Almanza
MARINE...Vaughan
FIRE WEATHER...M Ballard