375
FXHW60 PHFO 181323
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
323 AM HST Fri Jul 18 2025

.SYNOPSIS...
The downstream pressure gradient from a near stationary area of
surface high pressure far northeast of the islands will maintain
light to breezy trades the next several days. Lessened stability
from a weak upper low northwest of Kauai, along with higher
moisture pooling north of the state, will increase shower
frequency and coverage primarily north of the island chain through
Monday. There is a decent chance for periods of heavy rain on or
around Kauai with low probabilities for isolated weekend storms.
Stable, drier weather is expected to return early next week.


&&

.DISCUSSION...
A relatively quiet early Friday morning precipitation-wise as the
islands lay under weak ridging and drier air advects in on moderate
trades. High level clouds are rotating clockwise across the area
as upper convective cirrus blow off southwest of the chain gets
caught up within the upper level flow around the ridge. Thursday
evening`s highest rainfall focused along windward Big Island
where a few South Hilo sites picked up a quick quarter to half of
an inch. Generally, light trades rule with the exception of the
windier windward exposures/interior channels and wind-sheltered
leeward slopes where drainage breezes blow offshore.

A pattern change developing today will increase weekend rainfall
over the more western islands of Oahu and Kauai and waters
generally north of 21N latitude. Stability will begin to erode
today with the evolution of a weak mid to upper level low forming
just north northwest of the state in tandem with a mid level
trough moving in from the east. These features will likely provide
a boost in rain chances mainly north of the islands with higher
precipitation passing into Oahu and Kauai later tonight through
Sunday. The pros for more widespread rainfall will be falling
heights, enhanced upper level vorticity, and a surge of
unseasonably high moisture advecting in on modest trades,
deepening the resident boundary layer. The majority of the GFS
and EC ensemble guidance QPF members still depict a distinct swath
of higher rain paralleling 20 to 25 N. While confidence is
moderately high that more western islands will experience a wetter
weekend (than the eastern half), the chance of thunderstorms remains
fairly low. Upper levels should cool enough to provide the needed
instability required to place isolated storms in northern Kauai
and surrounding waters from late Saturday through early Monday.
The proximity of the low across the far northern maritime will
likely focus organized convection over the far northern offshore
waters this weekend. The timing of the heaviest rain will depend
upon the evolution of the upper low in conjunction with the
greatest moisture.

A stable summer-like trade wind pattern will return by late
Monday as lingering moisture advances west and drier air filters
in its wake. The upper level low will no longer be an issue from
Tuesday onward as it meanders off to the northwest and ridging
re-establishes itself over the islands.


&&

.AVIATION...
Moderate to locally breezy trade winds will prevail across the
islands with occasional passing showers favoring the typical
windward and mountain locations. Periods of MVFR ceilings and
visibility in SHRA will be confined to windward areas of all
islands, as well as the South Kona slopes of the Big Island during
the afternoon and evening hours. Otherwise, VFR conditions are
expected.

Due to the locally breezy trades, AIRMET Tango for low level
turbulence below 7,000 feet will continue through the day before
wind speeds gradually decline tonight. AIRMET Sierra is also in
effect for mountain obscuration over the N through E sections of
the Big Island through the morning hours.


&&

.MARINE...
High pressure will remain nearly stationary far northeast of the
state through the middle of next week. Fresh to locally strong
trades will persist through the day then drop slightly as a weak
low- level trough moves through the state from the east through
the weekend. The Small Craft Advisory (SCA) is currently in effect
through this afternoon for the windier waters and channels around
Maui County and the Big Island. The SCA will likely be scaled
back to just the Alenuihaha Channel through tonight. Trade winds
will continue to gradually decline to gentle to locally fresh
through the forecast period.

A mixed southerly swell will provide average surf along south
facing shores through early Saturday. A new small, long period
southwest swell will fill in slowly Saturday, peak over the
weekend before declining slowly through early next week.

Surf along east facing shores will continue to remain choppy due
to the fresh to locally strong trade winds before declining
slightly over the weekend. Surf along north facing shores will
remain nearly flat through the forecast period.

Peak high tides associated with the lunar cycle could lead to
minor coastal flooding along shorelines and low-lying coastal
areas next week Monday through Wednesday during the daily peak
tide each afternoon.


&&

.FIRE WEATHER...
Fire weather concerns will be low this weekend as a result of a
more wet pattern. Trade winds will remain light to locally breezy
the next several days with a higher frequency of showers. Drier
weather is expected to return early next week. This may increase
the fire weather threat over those leeward areas that may not
receive the full benefit of significant weekend rain.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST this evening for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.


&&

$$


DISCUSSION...Blood
AVIATION...Shigesato
MARINE...Shigesato
FIRE WEATHER...Blood