Sliding Sands Trail, Hawaii Weather Forecast Discussion

516
FXHW60 PHFO 301338 CCA
AFDHFO
Area Forecast Discussion
National Weather Service Honolulu HI
333 AM HST Tue Sep 30 2025
.SYNOPSIS...
The subtropical ridge north of the Hawaiian Islands will slowly
weaken this week with light to moderate trade winds in the
forecast lasting through Wednesday. The ridge north of the islands
will weaken and winds will veer out of an east to southeast
direction from Thursday onward, allowing an expansion of onshore sea
breezes over each island during the daylight hours.An unstable band
of clouds, the remnants of an old East Pacific cold front, will
drift through the islands on the trade winds from Wednesday morning
into Thursday enhancing showers statewide. Unsettled bands of
showers will continue to ride into the islands from Thursday on into
the weekend.
&&
.DISCUSSION...
The satellite picture this morning shows a weakening upper low
with embedded thunderstorms roughly 400 miles northwest of Kauai.
Bands of stable stratocumulus clouds are drifting into the islands
on the moderate easterly trade winds today. An unsettled cloud
band roughly 230 miles northeast of the state continues to ride
towards the island chain. Upper air balloon soundings at Lihue and
Hilo from 2 AM HST (12Z) this morning show subsidence temperature
inversion heights today in the 5,000 to 6,000 foot elevation
range. At this range only brief passing showers are forecast,
mainly limited to windward and mountain areas. These stable
weather conditions will continue through tonight.
Trade wind speeds will trend lower this week as the high pressure
ridge north of the islands weakens in response to a passing high
latitude cold front. A band of unstable clouds associated with an
old East Pacific cold front will ride into the islands from early
Wednesday morning into Thursday. Expect wet weather conditions
during this time period as these unstable clouds are forced
orographically over island mountain ranges. The best shower
coverage and rainfall amounts will favor windward island mountain
ranges during this time period. Some of the stronger showers with
this system will reach the drier leeward areas.
These weakening trade winds will veer from a more east to southeast
direction from Thursday onward. Decreasing large scale winds will
allow thermally driven local scale sea breezes to strengthen
during the daylight hours over all islands. Shower trends in this
sea breeze pattern will tend to favor island mountain and interior
sections each afternoon. The latest weather model solutions also
show good chances for converging winds along the leeward sides of
island mountains producing shower bands extending from west to
northwest of each island. These developing shower bands may
briefly enhance rainfall amounts over Oahu and Kauai in this
southeasterly wind regime from Thursday through Saturday.
&&
.AVIATION...
Moderate trade winds will persist through the forecast period
with clouds and showers focused mainly over windward and mauka
areas. An uptick of moisture is expected tonight through Wednesday
from remnants of an old frontal band. Localized MVFR possible
within passing showers, but most sites will remain VFR.
AIRMET Sierra remains in effect for mountain obscuration due to
low clouds and showers over windward Big Island. Conditions
expected to improve later this morning but may return tonight.
&&
.MARINE...
Moderate to locally fresh easterly trade winds will persist
through Wednesday before slowly diminishing through the latter
have of the week into early next week.
A small medium period north swell filled in yesterday and will
gradually fade today. A series of small medium period swells from
the north and northwest will trickle in through the rest of the
week. A moderate medium period northwest (330 degrees) swell is
expected to arrive on Saturday and Sunday, building surf heights
along north and west facing shores late this weekend into early
next week.
A series of small medium period south swells will keep surf along
south facing shores from going flat through the week.
Surf along east facing shores will remain on the small side in
moderate trade wind flow, despite some small medium period swell
moving into the region over the next couple of days from former
tropical cyclone Narda.
&&
.FIRE WEATHER...
Wind speeds will remain below critical fire weather thresholds for
the next seven days. Temperature inversion heights near the Big
Island and Maui will range from 5,000 to 6,000 feet today.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION...Bohlin
AVIATION...Shigesato
MARINE...Walsh
FIRE WEATHER...Bohlin

NWS HFO Office Area Forecast Discussion