Mililani Town, Hawaii 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

701
FXHW60 PHFO 220634
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
834 PM HST Sat Dec 21 2024

.SYNOPSIS...
Light and variable winds continue through Sunday evening as a cold
front passing north of the state will weaken the subtropical
ridge. A high pressure system will move in and build north of the
state from Sunday night into Tuesday causing the winds to briefly
shift back to trade winds with a few showers windward and
mountain areas. Another stronger cold front approaching the Hawaii
region from the northwest will weaken the ridge once again and
produce another light southeasterly wind pattern from Wednesday
onward. A shallow cold front may stall out near Kauai and Oahu by
next weekend producing a brief period of light showers.

&&

.DISCUSSION...
The subtropical ridge remains locked in place over the Hawaiian
Islands this evening producing stable and dry conditions across
the region. The satellite picture this evening reflects this
picture with almost no clouds around the Hawaiian Islands. A cold
front passing north of the island chain will keep large scale
winds light and variable through the weekend, with mostly sunny
skies, onshore sea breezes during the day and offshore land
breezes at night.

A brief weather pattern shift starts on Sunday night, where a
building high pressure system passing north of the islands will
bring moderate to locally breezy trade winds back into Tuesday.
By Tuesday the high center will continue to drift farther
eastward into the East Pacific basin. A cold front approaching the
islands from the northwest will weaken the ridge north of the
state and force the ridge axis to drift south over the Hawaiian
Islands. This pattern change will bring another round of stable
and dry conditions, with light southeasterly winds with expanding
sea breezes from Wednesday through Friday.

A shallow cold front will move into and stall out over the western
islands of Kauai and Oahu by Friday. Clouds and a few showers are
possible along this weakening frontal band. However fairly stable
conditions under the ridge will limit rainfall amounts with this
next system. Islands in Maui and Hawaii Counties will likely not
see much rainfall activity with this next frontal system. Trade
winds return next weekend with an upper level trough/low
potentially enhancing windward and mountain shower activity.

&&

.AVIATION...
A strong surface ridge over the Hawaiian Islands will keep light
winds over the area. Sea/land breezes expected through the
weekend. Some brief SHRA and MVFR conds are possible but VFR conds
should prevail.

No AIRMETs in effect.

&&

.MARINE...
Hazardous marine conditions will persist into early next week,
with the largest in a series of extra-large, overlapping northwest
swells arriving late tonight. Offshore buoys northwest of Kauai
have begun registering long-period energy (0.98 ft at 30 seconds)
this evening, with upstream SOFAR drifter buoys starting to
climb--signaling the anticipated arrival of the swell as predicted.
Combined with satellite data and SOFAR drifter buoy measurements
of wave heights exceeding predictions Friday night far north of
Hawaii, confidence is increasing that this swell will arrive on
schedule and may exceed earlier forecasts. The southward extension
of this fetch to within 700 nautical miles of the islands earlier
further reinforces this confidence. The swell will build rapidly
late tonight, peak through the day Sunday, and gradually ease
Sunday night through Tuesday. Resulting surf should be giant, in
excess of 40 feet (faces) along coastlines with the highest
exposure, during the peak Sunday. Heights could hover at or above
warning levels well into Monday before lowering to advisory levels
by Tuesday.

This extended period of warning-level surf, which began
Wednesday, will produce significant coastal impacts, including
considerable beach erosion along exposed shorelines and potential
overwash onto vulnerable coastal roadways and properties,
particularly during the peak on Sunday. These impacts will remain
likely despite monthly tidal minima, underscoring the magnitude of
this swell. Mariners should also anticipate hazardous conditions,
including strong currents and occasional breaking waves near
harbor entrances, making transits potentially dangerous.

Winds across coastal waters will remain light and variable through
Sunday as a surface ridge lingers over the region. However, a
fast-moving surface high approaching from the northwest will lead
to a rapid increase in northeast winds Sunday night, followed by
fresh to strong trade winds as the high passes north of the state
on Monday. A Small Craft Advisory (SCA) remains in effect for seas
exceeding 10 feet, and as winds increase, the SCA will be expanded
to include wind-affected zones. Trades are expected to gradually
decline and shift southeasterly on Tuesday and Wednesday as the
high moves eastward.

&&

.FIRE WEATHER...
No critical fire weather conditions are expected for the next
seven days. Dry humidity levels will continue in a mostly lighter
wind pattern. Wind speeds will be the limiting factor as drier
leeward afternoon humidity levels continue to approach criteria
for some of our fire zones on the Big Island.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Warning until 6 AM HST Monday for Niihau-Kauai Leeward-
Waianae Coast-Oahu North Shore-Maui Windward West-Kona-Kohala-
Kauai North-Molokai Windward-Molokai North-Molokai West-Maui
Central Valley North-Windward Haleakala.

High Surf Advisory until 6 AM HST Monday for Big Island East-Big
Island North.

Small Craft Advisory until 6 AM HST Monday for all Hawaiian
waters except Maalaea Bay-

&&

$$

DISCUSSION...Bohlin
AVIATION...Walsh
MARINE...Gibbs
FIRE WEATHER...Bohlin