261
FXHW60 PHFO 240649
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
849 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 mid-level low north of Kauai continues to produce isolated
thunderstorms near the core this evening. Most of these
thunderstorms have remained outside the coastal waters, however
some lightning has been observed west of Niihau. The thunderstorms
near Niihau are expected to move to the west over the next couple
of hours as the mid-level low, and its associated surface trough,
move west.

Light to moderate trade winds continue across the islands due to a
pair of high pressure systems northwest and northeast of the
islands. The above mentioned surface trough, along with a front
passing north of the islands between the above mentioned highs,
are helping to keep the trades on the lighter side tonight.

With the proximity to the mid-level low, showers near Kauai and
Oahu could be briefly heavy tonight, and we are seeing that on
radar mainly with some showers over the waters to the lee of Oahu
and Niihau. Otherwise, more typical trade wind showers are
expected. Low clouds moving towards the Big Island this evening
on the trade wind flow will keep showers over the windward and
southern slopes through the first part of tonight, with some
improvement expected by early Tuesday morning.

As the mid-level low moves to the west over the next several days,
expect a more stable airmass so move over the area. As the mid-
level low moves west, some high clouds are likely to stream over
the islands from the south at times. Meanwhile the high pressure
systems to the north will consolidate into a single center north-
northwest of the islands, and trade winds will strengthen just a
bit over the next couple of days. Expect minimal showers with the
more stable airmass, mainly impacting the windward areas into
next weekend. Lighter winds are possible by next weekend as a new
low passes N of the islands.


&&

.AVIATION...

Moderate trades will continue to deliver clouds and showers to
windward areas into tomorrow and strengthen slightly to become
locally breezy. Deeper moisture moving into the Big Island and
Maui from the east will continue to 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 will fill in behind this batch of
showers, leading to improving conditions and prevailing VFR during
the day tomorrow.

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


&&

.MARINE...
A weak trough of low pressure passing northwest of Kauai tonight
is producing isolated thunderstorms over the northwest offshore
waters and far west coastal waters. As the trough moves west, the
threat for thunderstorms will continue to exist over the western
offshore waters through Tuesday. Low pressure moving east across
the Gulf of Alaska will ride atop a large area of high pressure
centered north of the state. This may push the high slightly
closer to the islands but have little to no affect on generally
moderate trade winds the next several days. A Small Craft Advisory
may be necessary for the windier waters surrounding Maui County
and Big Island from Tuesday onward as winds near advisory
thresholds.

Surf along north and west-facing shores will remain very small
this evening. A small to moderate size, long to medium period
northwest swell (320-330 degrees) originating from a passing North
Pacific cold front is timed to arrive at the northwest offshore
buoys late tonight and be passing around Kauai and Oahu Tuesday
afternoon and evening. This swell will peak Tuesday night and
Wednesday morning, lifting north surf to well above head high
along reefs and shorelines where northwest energy will best focus.
North shore surf is expected to remain well under the High Surf
Advisory levels and gradually decline from Wednesday afternoon
onward. Surf along south-facing shores may experience a series of
small, long period southwest pulses at the end of the month in
relation to storms that are passing south of the Tasman Sea and
New Zealand early this week. A very small fetch area of strong
southwest winds about 1,000 miles southwest of Oahu associated
with strong thunderstorm activity today may bring in small period
energy from the west southwest Wednesday into Thursday. East-
facing shore chop should remain small through much of the week due
to the lack of locally strong trades over or upstream of the
state.


&&

.FIRE WEATHER...
Although the mid-level low has introduced some instability to the
area weather, afternoon relative humidity levels reached into the
mid to upper 40s Monday afternoon, and winds were just below
criteria. With a slightly drier airmass expected to move in, and
with winds expected to nudge upwards, we will have to keep an eye
on elevated fire weather concerns.


&&

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

&&

$$


DISCUSSION/FIRE WEATHER...M Ballard
AVIATION...Farris
MARINE...Blood