504
FXHW60 PHFO 210147
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
347 PM HST Mon May 20 2024

.SYNOPSIS...
The low pressure system far north of the state will continue to
drift slowly northward over the next few days as high pressure
builds back into the region. Expect moderate to locally breezy
east to east-southeast winds over most islands through midweek,
though daytime sea breezes will occur over sheltered areas of
each island. Brief passing showers will favor mainly windward and
mountain areas. A disturbance will move through the islands from
Tuesday night through Thursday morning, increasing windward and
mauka showers.

&&

.DISCUSSION...
Locally breezy east-southeast flow is prevailing over the eastern
end of the state today, with more moderate winds farther west as
the low pressure system far north of the islands gradually lifts
northward. Within this east-southeast flow regime, showers and
clouds have been common today across windward and southeastern
sections of the Big Island. Additionally, daytime sea breezes over
areas sheltered by island terrain have increased clouds over
select inland and leeward locations as well, but afternoon
soundings at Hilo and Lihue reveal a strongly capped environment
which has limited overall shower potential.

Expect moderate to locally breezy east to east-southeast winds
over the eastern half of the state and moderate winds over the
western half into Tuesday. Localized sea breezes will be possible
during the daytime over sheltered areas again Tuesday. This will
again cause clouds to build over island interior sections though
overall shower activity will remain limited.

Low pressure aloft associated with the kona low to the north of
the state will swing around and develop into a new trough and
eventual low in the mid- to upper levels. A weak surface low is
forecast to develop along a trough just south of 30N by Thursday.
Meanwhile, a developing shortwave aloft will move into the
eastern islands late Tuesday. This could increase moisture depth
and result in and increase in windward and mauka showers spreading
across the island chain from west to east from Tuesday night
through Thursday morning, particularly during the overnight
through early morning hours.

From Thursday through the rest of the week, trade winds spread to
all islands. Broad upper level troughing will keep passing
showers mainly during the overnight to early morning hours
favoring windward and mountain areas.

&&

.AVIATION...
A surface trough to the west and continuing to move away from the
area will allow a surface trough north of the islands to
strengthen. This will allow light to moderate east to southeast
winds to transition to moderate trade winds tomorrow.

While VFR conditions continue to prevail over the smaller islands,
clouds and showers that have developed over the Big Island have
led to the issuance of AIRMET Sierra for mountain obscuration.
Expect conditions to improve after sunset.

No additional AIRMETS are expected into tonight.

&&

.MARINE...
A trough of low pressure just west and northwest of the state will
continue to linger through the first half of the week. Meanwhile,
a strong high will remain nearly stationary far northeast of the
state through most of the week. The combination of the trough to
our west and the high to the northeast will produce locally strong
trades over the eastern half of the state and moderate trades
over the western half through Tuesday. A Small Craft Advisory is
in effect for the windier zones around Maui County and the Big
Island. Starting late Tuesday night into Wednesday, another trough
will develop west of the state and will cause the winds to weaken
and veer toward the southeast over the western half of the state.
By Thursday, the trough should weaken and we should see fresh to
locally strong trades across the state through the rest of the
work week. Trades may weaken a touch over the weekend as the high
far northeast of the state weakens.

Surf along south-facing shores will continue to gradually decline
over the next several days. Near-shore buoys did show a decline
below high surf advisory thresholds, thus the High Surf Advisory
has been cancelled. Surf heights should continue to remain above
the summer average (5 feet) through Tuesday then dissipated around
Wednesday. A gale force low currently in the South Pacific near
36S120W showed winds near storm force directed toward the state on
the OSCAT pass yesterday. This does increase the potential for a
small southeast swell Friday into the weekend. Surf along east
facing shores should see a gradual rise over the next several days
as the trades strengthen upstream of the state.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 7 AM HST Wednesday for Pailolo
Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island
Southeast Waters.

&&

$$

DISCUSSION...Vaughan
AVIATION...M Ballard
MARINE...Kino