Kahului, Hawaii 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

942
FXHW60 PHFO 191410
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
410 AM HST Sat Jul 19 2025

.SYNOPSIS...
Lessened stability from a weak upper low northwest of Kauai,
along with higher moisture pooling over and north of the islands,
will increase statewide shower frequency and coverage. There are
moderate chances for periods of heavy rain across the western end
of the state with low probabilities for isolated storms over the
north nearshore waters. Stable, drier weather is expected to
return early next week where trade showers will favor windward
exposures and upslope mauka.


&&

.DISCUSSION...
The wetter pattern commenced overnight as a more moist air mass
moved in from the east. It has been a fairly wet early Saturday
for Oahu and Maui where many sites have picked up a quick quarter
to over an inch of rain the past six hours. Windward mauka are
registering higher amounts where some upslope gauges have measured
near an inch and a half since late last night. This wet pattern
will persist into Sunday as an upper low northwest of the state
and associated mid level trough passes through and taps into a
more moisture-rich air mass. Both 12Z soundings came in at 1.47
inch pwats or near the 75% climate percentile for mid to late
July. Upper air soundings also depict the erosion of the low level
temperature inversion in response to the decreasing stability.
The westward passing 700 mb trough axis and cooling initiated by
lowering heights to the northwest will maintain a deeper, more
moist boundary layer.

Stability will continue to erode through the day as a result of
the evolution of the northwest upper low in tandem with the
passing mid level trough moving in from the east. These features
have and will provide a boost in rainfall with the highest rain
falling along windward exposures and adjacent nearshore waters.
The majority of the GFS and EC ensemble guidance QPF members still
depict a distinct swath of higher rain falling between 20 to 25
N. The forcing of the weak low across the far northern maritime
will focus better organized convection over the far northern
offshore waters into early next week. While confidence is
moderately high that more western islands will experience a wetter
weekend, the chance for thunderstorms remains relatively low.
Upper levels should cool enough to provide the needed instability
required to place isolated storms in the proximity of northern
Kauai and surrounding waters later today through early Monday. The
timing of the heaviest rain will depend upon the evolution of the
upper low in conjunction with the greatest pooling moisture.

A stable summer-like trade wind pattern will return by late
Monday as lingering moisture advances west and drier air filters
into 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. A northern weak
mid level shortwave trough may brush the western end of the state
Wednesday. This feature may briefly enhance trade wind showers
across the western half of the state. In closing out the week,
model guidance does hint of a trough approaching from the east
that would briefly disrupt trade flow...weakening winds as they
back a touch more northeast.


&&

.AVIATION...
High pressure far to the north will drive moderate to locally
fresh trade winds across the state. An area of cloud and showers
is expected to continue from the east later today and will likely
bring periods of MVFR conditions along windward slopes.

AIRMET Tango is in effect for tempo moderate turbulence below 070
across all leeward areas. This AIRMET may be able to be dropped
later this morning as winds weaken slightly. AIRMET Sierra is
also in effect for mountain obscuration over the N through E
sections of all islands through the morning hours.


&&

.MARINE...
High pressure will remain nearly stationary far northeast of the
state through the middle of next week. A weak low-level trough is
expected to move through the state from the east through Sunday,
weakening the trade winds. The Small Craft Advisory (SCA) for the
windier waters and channels around Maui County and the Big Island
has dropped this morning and 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 the morning. The new small long period
southwest swell has begun to slowly fill in with long period
forerunners showing up on the nearshore buoys early this morning
and is expected to continue to fill in through the afternoon, peak
late tonight then decline slowly through early next week.

Surf along east facing shores will gradually decline over the
weekend with the weakening trade winds. 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...
None.

&&

$$


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