392
FXHW60 PHFO 241332
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
332 AM HST Tue Sep 24 2024

.SYNOPSIS...
Moderate trade winds will strengthen some today, and remain
locally breezy through the rest of 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...
Several changes to the forecast were made with the morning
package. The PoPs have been lowered a bit over the islands for the
next several days, following the National Blend of Models (NBM)
drier trend. Winds have been nudged upwards over the next couple
of days as expected, keeping in line the NBM and other recent runs
of high resolution models. This has prompted the issuance of a
Small Craft Advisory for some coastal waters, see the Marine
section for more details.

The synoptic features haven`t changed much since last night. The
mid-level low, along with its thunderstorms, have moved to the
west, and is about 140 miles northwest of Kauai early this morning.
The associated surface trough has also moved to the west, and
this is allowing the trades to rebound a bit. The overnight
ASCAT-C pass missed the islands, but the ASCAT-B clipped the
eastern edge of the Big Island, and showed the upward trend that
we were expecting.

As the mid-level low and its instability move to the west, the
airmass over the islands is expected to become more stable, which
will lead to a downward trend in shower activity. Thus the
decrease in PoPs in the forecast as noted above. The trade wind
regime will help to focus any showers to the windward slopes of
the islands. Despite a more stable airmass overhead, some clouds
and showers could form over the leeward slopes of the Big Island
during the afternoon hours.

As expected with the mid-level low moving to the west, some high
clouds are being carried to the northeast over the islands. Expect
some of these high clouds to remain in the area for the next
couple of days.Lighter winds are possible by next weekend as a
new low passes north of the islands.


&&

.AVIATION...
Moderate trades will become locally breezy later today and
continue to deliver clouds and isolated to scattered showers to
windward and mauka areas. VFR conditions will generally prevail,
but MVFR conditions will be possible in any showers.

No AIRMETs are currently in effect and none are anticipated to be
needed today.


&&

.MARINE...
A trough of low pressure passing west over the far northwest
offshore waters this morning may produce isolated thunderstorms
over the far western Hawaiian Island waters through the day. Low
pressure moving east across the Gulf of Alaska will ride atop a
large area of high pressure centered north of the islands. This
may push the high slightly closer to the islands but this will
have little to no effect on moderate to locally strong trades the
next several days. A Small Craft Advisory is in in effect for the
windier waters surrounding Maui County and Big Island through
Wednesday afternoon.

A small to moderate size, long to medium period northwest swell
(320-330 degrees) arrived at the northwest offshore buoys last
night and is timed to reach Kauai before sunrise, Oahu around
sunrise. This swell will peak tonight into Wednesday morning and
lift north surf to well above head high along those reefs and
shorelines where northwest energy best focuses. Surf from this
swell is expected to remain under the High Surf Advisory heights
and gradually decline beginning Wednesday afternoon. Surf along
south-facing shores may experience a series of small, long period
southwest pulses at the end of the month in response 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 in association with recent strong
thunderstorm activity 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
a strong trade fetch over or upstream of the state.


&&

.FIRE WEATHER...
KBDI values remain near 626 today. The minimum relative humidity
this afternoon could drop into the mid 40s today, while winds are
on the uptick. This could bring us close to red flag conditions
for a brief time this afternoon. Models show that afternoon
relative humidity shouldn`t be as low tomorrow afternoon, but
winds will remain locally breezy through much of the week.


&&

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


&&

$$


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