Kapaau, Hawaii Weather Forecast Discussion

914
FXHW60 PHFO 231333
AFDHFO
Area Forecast Discussion
National Weather Service Honolulu HI
333 AM HST Tue Sep 23 2025
.SYNOPSIS...
Locally breezy trade winds will ease later today and Wednesday as
as developing surface low far northeast of the islands weakens
the local pressure gradient. Showers will be focused over windward
slopes, and while most leeward areas will experience minimal
shower activity, the Kona slopes of the Big Island will see
scattered afternoon and evening showers, some briefly heavy. The
surface low will drift north of the islands on Thursday,
disrupting trade winds and leading to a land and sea breeze
pattern with localized heavy showers into the weekend.
&&
.DISCUSSION...
Moderate to locally breezy trade winds will hang on for one last
day. The Northeast Pacific surface ridge that had been driving
the trade winds during the past several days has been eroded by an
advancing front located about 700 miles north of Kauai. A North
Pacific surface high building behind the front will keep moderate
to locally breezy trade winds only a notch lighter than yesterday.
Meanwhile, an upper-level trough that has been parked just north
of the islands during the past few days will be pushed southward,
leading to slight instability. Since there are no organized areas
of moisture moving along the trade wind flow, the main impact of
the instability will be another round of localized heavy showers
on the Kona slopes of the Big Island this afternoon and evening.
Otherwise, expect typical windward rainfall of less than a half
inch today, with minimal leeward shower activity elsewhere.
Trade winds will gradually ease tonight and Wednesday. Trades
will weaken as the local pressure gradient relaxes in response to
surface low pressure forming about 750 miles northeast of the
islands along the stalling front mentioned above. Expect showers
to continue to favor windward slopes and the Kona Districts of the
Big Island, and as the upper-level trough supporting the surface
low digs over the islands on Wednesday, an isolated heavy shower
will be possible, mainly over leeward and interior Big Island.
Trade winds will become disrupted by Thursday as the surface low
moves to about 400 miles north of the islands. The GFS and ECMWF
are suggesting that the low could push a band of deeper moisture
as far south as Kauai through Saturday. The latest runs of the
GFS and ECMWF have trended the upper-level forcing slightly
stronger over Kauai, where there will be some chance for heavy
showers and potential flooding. The rest of the island chain will
be under a light southerly flow with less available moisture,
resulting in a land and sea breeze pattern with spotty afternoon
showers. Away from the higher moisture near Kauai, dew points are
not expected to creep up much more than to around 70. In spite of
this, the lack of trade winds will produce a humid feel.
Sunday and Monday, the low will fill and drift westward, likely
allowing a light east-southeast flow to build over the island
chain.
&&
.AVIATION...
Trade winds will gradually ease as a cold front far to the north
advances southeast. Showers will continue to favor north through
east sections of the islands, with predominately VFR conditions
to prevail at most locations through the forecast period.
No AIRMETs currently in effect.
&&
.MARINE...
Moderate to locally fresh trades prevail through Wednesday, then
a developing low pressure system northeast of the islands weakens
large scale wind speeds, and winds will become light and variable
from Thursday through Sunday. Light trade winds begin to return to
the Hawaii region from next week Monday into Tuesday.
The next small south swell builds in today, peaking overnight,
and then slowly declining on Wednesday. The next, small long
period south swell will fill in from Thursday into next weekend.
Surf heights from these swells will remain near seasonal averages
along south facing shores.
A trough northeast of Hawaii will generate a short period fresh
north swell that will reach the islands by Wednesday night, and
then peaking from late Thursday into Friday. This swell may bring
small to moderate surf along exposed shorelines. Evolution of
this trough and its close proximity to the islands brings
increased uncertainty to the surf height forecast this week
along north and east facing shores.
&&
.FIRE WEATHER...
In spite of minimal rainfall over most leeward areas, declining
trade winds will ensure that conditions remain below critical
thresholds today and Wednesday. Lighter winds with afternoon sea
breezes are expected Thursday into the weekend.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION...Wroe
AVIATION...Shigesato
MARINE...Bohlin
FIRE WEATHER...Wroe

NWS HFO Office Area Forecast Discussion