Waihee-Waiehu, Hawaii 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

106
FXHW60 PHFO 201400
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
400 AM HST Sun Jul 20 2025

.SYNOPSIS...
Weak low pressure far northwest of the islands will move further
off to the west as high pressure expands over the Central Pacific.
Greater lower to mid layer moisture will thin out as drier air
moves in from the east the next few days. Coastal and higher
terrain trades will generally remain moderate with locally strong
winds through the middle of the week. Showers will become less
frequent and focus along windward upslope mauka exposures.


&&

.DISCUSSION...
The influence of a passing mid level trough across the western
third of the island chain, along with weak upper low north
churning near 35N165W, within a lingering moisture rich air
resident mass provided enough instability to develop overnight Oahu
plume and northern moving rain that trained over the Garden
Island. The heaviest rain fell parallel to Kauai`s high ridgelines
with half an inch to inch hourly rates lifting local streams
downstream of Mount Waialeale (Wainiha) to flood stage. The
trajectory of the precipitation south of Kauai is now sliding a
touch more west and away from Kauai thus lessening the morning
threat. Many higher elevation regions within central and northern
Kauai picked up about one to two inches since last night with
neighboring Oahu receiving a few tenths an inch more rain within
the Manoa and Nuuanu Valleys since yesterday evening. A drier air
mass moving in from the east will suppress widespread rain with
widely scattered light showers sticking to windward exposed
upslope mauka through the week. This drier week will likely
exacerbate short term fire weather conditions as the state will
fall deeper into abnormally dry to moderate drought categories
(see Fire Weather section below). Surface high pressure far north
northeast of the state will continue to produce a gradient tight
enough to drive moderate to locally strong trade winds over the
islands for the next few days.

Lowering heights slinking away to the northwest, as ridging at
all levels takes hold from the south and east, will ensure a more
stable environment for the week to come. The dry air has yet to
arrive as Hilo`s 12Z sounding is showing a saturated layer up to
800 mb (7 k ft) within a very moist air mass of near 1.75 inch
pwats which is in the lower 10% of climatological occurrence.
Upper ridging will anchor itself over the southern latitudes and
will directly influence late July drier island weather. The
approach of a shortwave mid level trough from the east at mid week
may subtly weaken winds but limited moisture will maintain
statewide low rain chances. The drier trend is supported by the
both ensembles where the majority of the members keep the diurnal
periods of higher QPF either north or south of the island
archipelago. Slightly weaker synoptic trade flow may allow local
breezes to take over and create their own micro-climates (e.g.,
afternoon Big Island kona slope sea breeze showers).


&&

.AVIATION...
High pressure far north of the islands will maintain moderate to
locally breezy trades through the weekend. Lingering instability
associated with a weak upper level disturbance north of Kauai and
a moist air mass across the state will result in periods of MVFR
showers across mainly windward and mauka areas through Sunday,
with some showers moving into leeward areas overnight. Isolated
thunderstorms are also possible across the waters north and east
of Kauai through late tonight.

AIRMET Sierra for mountain obscuration remains in effect for
windward sections of Kauai and Oahu. With little change expected
overnight.


&&

.MARINE...
A trough passing westward near Kauai will allow the high pressure
to build back into the region and strengthen trade winds into the
moderate to locally strong range into the middle of next week.

Several pulses of southerly and southwesterly swell will continue
to boost surf heights along south and some of the west facing
shores this week.

Surf along east facing shores will remain small and choppy. 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...
Due to recent rain, statewide fire weather concerns will remain
low to begin the week. Drier conditions this week will begin to
awaken a heightened situational awareness to the increased
wildfire threat. KDBI values exceeding 600 with afternoon
humidities falling into the lower to mid 50s under lighter
interior winds should hold the near to medium term fire threat at
bay.


&&

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


&&

$$


DISCUSSION...Blood
AVIATION...Bohlin
MARINE...Bohlin
FIRE WEATHER...Blood