149
FXHW60 PHFO 240215
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
415 PM HST Mon Sep 23 2024

.SYNOPSIS...
Moderate trade winds will strengthen somewhat through Tuesday, and
remain locally breezy through the week. Lighter winds are possible
by the weekend. Passing showers will favor windward areas, with
some afternoon showers over the Big Island`s leeward slopes.

&&

.DISCUSSION...
A closed mid-level cutoff low centered less than 100 miles N of
Kauai is producing isolated thunderstorms near its core, and has
destabilized the atmosphere in its vicinity. Afternoon sounding from
PHLI indicates a lack of a subsidence inversion, while a weak
inversion near 8000` was noted at PHTO. Meanwhile, light to moderate
trade winds are being driven by a pair of high pressure systems
centered NW and NE of the islands. A weakness in the ridge far N of
the islands is due to a passing front, while the low aloft has also
induced a surface trough just N of the islands, resulting in trade
wind speeds on the lighter side.

Visible satellite indicates limited low clouds immediately upstream
of the smaller islands, with an area of increased low clouds moving
into windward Big Island from the E. This area will fuel increased
shower coverage there this evening before diminishing after
midnight. Elsewhere, brief and passing showers will favor windward
areas overnight and early Tuesday, with the instability potentially
allowing a few showers to become briefly heavy over Kauai and Oahu.

The mid-level low is forecast to move W at a fairly good clip over
the next several days, with a mid-level high moving over the area
from the E. This will lead to increased stability through the week,
and a brief period of increased high clouds late tonight and
Tuesday. Trade winds will strengthen subtly over the next couple of
days as the nearby surface trough moves W, and the surface highs
consolidate into a single center NNW of the islands. The resulting
weather pattern is expected to provide only minimal showers, mainly
windward, into next weekend. Lighter winds are possible by next
weekend as a new low passes N of the islands.

&&

.AVIATION...
Moderate trades remain on the drier side this afternoon with limited
cloud cover in most areas and only very spotty showers. Deeper
moisture east of the Big Island will advance westward across the
area tonight bringing periods of MVFR to windward and mauka zones.
Confidence in MVFR potential is highest over the eastern end of the
state. Drier air fills in behind this batch of showers leading to
high confidence in improving conditions and prevailing VFR by
daytime Tuesday.

No AIRMETs in effect. AIRMET Sierra for mountain obscuration may be
needed for windward and mauka portions of Big Island through Oahu
tonight.

&&

.MARINE...
A weak trough of low pressure passing north of Kauai today is
producing isolated thunderstorms over the NW offshore waters this
afternoon. The threat for thunderstorms will continue to exist over
the western offshore waters through Tuesday as the trough moves
westward. With the trough moving away, the pressure gradient will
tighten over the state and will lead to the trades strengthening on
Tuesday. Moderate to fresh trade winds should hold through most of
the week as a weak high remains anchored far north of the state.
Winds will be borderline SCA thresholds each day starting tomorrow
Tuesday for the typical windy waters of Maui County and the Big
Island.

A moderate long period northwest swell (320 to 330 degrees) is
expected to steadily fill in on Tuesday and peak late Tuesday into
Wednesday morning then gradually decline the rest of the work week.
A smaller north-northwest swell should provide a boost this weekend.
Surf along south facing shores should see a series of small long-
period southwest pulses through the weekend due to a series of
storms near the Tasman Sea last week. Additionally, a fetch of
strong southwest winds near 10N170W over the past 24 hours should
bring an increase of short-period energy from the southwest
Wednesday into Thursday. East facing shores should remain small
through much of the week due to the lack of strong trades locally or
upstream of the state.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Birchard
AVIATION...JVC
MARINE...Kino