200
FXHW60 PHFO 171842
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
842 AM HST Fri Oct 17 2025

.UPDATE...

Flood watch for Kuaui and Niihau has been cancelled as latest
radar and satellite data show minimal chance for flood-producing
rain over the next several hours. Heavy rain is still possible
tonight with stronger showers and any thunderstorms that may
develop.

&&

.SYNOPSIS...

An upper level low pressure system, currently situated a few hundred
miles west of Kauai, will slowly drift to the west southwest for
the next several days. Moderate to locally strong trade winds,
coupled with moisture and instability associated with the low,
will continue to bring enhanced showers and isolated thunderstorms
to much of the state through at least Saturday. Another upper
level low is forecast to drop southward towards the islands early
next week and maintain an unsettled weather pattern.

&&

.PREV DISCUSSION.../ISSUED 349 AM HST Fri Oct 17 2025/

Radar continues to indicate enhanced shower activity over mainly
northeast and eastern portions of all islands and adjacent coastal
waters. Overnight rainfall accumulation totals, however, have not
been overly impressive with less than an inch recorded for the
wettest standout locations. Unstable conditions aloft, as noted on
the 12Z Lihue RAOB sounding, along with low level convergent
boundaries, have aided in the development of thunderstorms just
south of Oahu and north of Kauai early this morning. A Flood Watch
has been issued for Kauai through noon to account for a cluster
of thunderstorms north of Kauai slowly sagging to the southward.
This Watch may need to be extended in time depending on the
evolution of complex later today.

An upper level low, centered roughly 200 miles west of Kauai, has
been responsible for the unsettled weather experienced over the
past 24 hours. Both the GFS and ECMWF prog the low to drift slowly
westward through Saturday. Thus, with the associated instability
still in place, moderate to locally strong trades will continue to
drive rounds of enhanced showers and isolated thunderstorms over
the state through early this weekend. Most heavy rain and
thunderstorm activity remain over Oahu, Kauai, and their
surrounding coastal waters, closest to the aforementioned low.
Shower activity may wane slightly Saturday morning into Sunday as
the upper level feature moves further west, away from the state.

The first upper low will be replaced by a second one late Monday.
This next one will stall to the northeast of the state and weaken
through mid week. However, an upper trough connecting the
remnants of the first low to our SW and the second one to the NE
will remain over the area. This feature should help to maintain
enhanced showers in a moderate to breezy trade wind pattern.

AVIATION...

An upper level low pressure system just west of the state will
continue to bring an unstable airmass with enhanced showers to the
entire area today. However, these showers will be mainly focused
along northeast and east portions of the islands. There will isolated
thunderstorms across the affect airports on Kauai and Oahu along
with areas over their adjacent coastal waters. Expect periods MVFR
conditions, along with isolated IFR ceilings and visibility in
some of the more robust showers and storms.

AIRMET SIERRA remains in effect for Big Island, Oahu, Kauai,
Molokai, and Maui above 2000 feet for tempo mountain obscuration
due to clouds and showers. SIERRA will likely continue through the
remainder of the day.

AIRMET TANGO is in effect for across the island chain for tempo
moderate turbulence between FL300 and FL350. This is expected to
through the remainder of the day.

MARINE...

Moderate to locally strong trades will remain in place over the
Hawaiian coastal waters through Saturday. Trade winds will weaken
hold in the fresh to moderate range through early next week. An
upper low north of Kauai continues to drifting southwestward into
the northern coastal waters today and will keep isolated
thunderstorms in the forecast over the waters into the weekend.
A Small Craft Advisory (SCA) remains in effect for windier waters
and channels surrounding Maui and the Big Island. The SCA was
expanded to include northern coastal waters near Kauai and Oahu.

Two moderate, long period NW and NNW swells moving through the
Hawaii region will keep surf heights elevated along N and W
facing shores through the end of the week. Surf along N and W
facing shores slowly trends down on Sunday. A hurricane force low
E of Japan will bring another round of moderate, long period
NW (330 deg) swell into the islands building surf heights along N
and W facing shores from next Wednesday onward. This next long
period swell may possibly reach low end High Surf Advisory levels
from Wednesday into Thursday if we add a one to two foot upward
adjustment to swell heights as compared to the ECMWF Wave model.

A series of small, medium to long period S to SW swells filter
into the area into the weekend, keeping S shores from going flat.
Short period surf along E shores picks up through the weekend as
trade winds strengthen.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST this evening for Kauai
Northwest Waters-Kauai Windward Waters-Kauai Channel-Oahu
Windward Waters.

Small Craft Advisory until 6 PM HST Saturday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.


&&

$$


UPDATE...Parker
DISCUSSION...Thomas/Almanza
AVIATION...Thomas/Almanza
MARINE...Bohlin
FIRE WEATHER...Thomas/Almanza