132
FXHW60 PHFO 090133
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
333 PM HST Wed May 8 2024

.SYNOPSIS...
Light to moderate trades will persist over the eastern islands
through Thursday, while lighter trades and leeward land and sea
breezes prevail over the western islands. Showers will favor
windward slopes and coasts at night and interior and leeward areas
each afternoon. Thunderstorms are possible Friday and Saturday as
an upper disturbance moves through. Conditions should improve
Sunday through early next week.

&&

.DISCUSSION...
High pressure far north of the main Hawaiian Islands drives light
to moderate trades across local waters this afternoon. Satellite
loop shows broken to overcast low clouds have spread westward
since this morning to cover mauka and leeward areas, while
adjacent waters have scattered low clouds to clear skies. Latest
soundings depict seasonal amounts of PW, between 1.2 and 1.4
inches of PW, and a neutral to slightly unstable airmass.
Subsidence inversions are rising and weakening, setting up
conditions which would allow showers to spread and shower-bearing
clouds to build higher. Radar shows scattered light to moderate
showers beneath cloud cover.

A front far northwest of the islands will shift southeastward
over the next couple of days, eventually weakening into a broad
trough across the islands on Friday. Trades will ease over the
next few days in response. Expect light to moderate trade winds
over the eastern islands tonight and Thursday, while lighter
trades allow development of land and sea breezes across leeward
areas of the western islands. Through Thursday, expect showers to
favor windward and mauka areas overnight and during the morning,
then transition over to interior and leeward areas each afternoon
into the early evening. As the boundary layer flow becomes light
and variable Thursday night, most showers should remain offshore.
Models show trades will decrease further on Friday, allowing for
sea breeze development statewide. Trades may strengthen over the
weekend as the broad trough gradually weakens. By early next week,
another front northwest of the state will cause surface flow to
veer to southeasterlies across the western islands while trade
flow persists across the eastern islands.

Models show an upper low will move across the chain Friday
through Saturday. Associated cold air aloft will destabilize our
airmass and introduce the possibility of thunderstorms. At this
time, predicted PW does not appear to be high enough to fuel a
widespread heavy rain threat. However, brief heavy downpours
associated with possible thunderstorms would cause minor flooding
impacts. We will monitor model depictions over the next few days
and issue appropriate watches if needed. Models also depict a
potential for severe thunderstorms, with steep lapse rates, high
CAPE, and strong bulk shear. If these conditions were to develop,
stronger thunderstorms would be capable of producing hail and
strong gusty winds. High resolution models covering our domain
will be available within the next 24 hours. Expect a return of a
hybrid trade wind pattern by Saturday night, featuring windward
and mauka showers at night, followed by interior and leeward
showers during the afternoon and early evening hours.

&&

.AVIATION...
Light to moderate trades will persist through Thursday with day
time sea breezes and night time land breezes expected over select
leeward areas. Scattered showers will continue to favor windward
and mauka areas and we are expecting an uptick of showers late
tonight into Thursday morning as a band of moisture approaches
from the east. As this moisture band moves in, MVFR conditions
will be possible for windward and mountain areas with VFR
conditions prevailing across leeward areas tonight through
Thursday morning. A disturbance aloft will begin to approach the
state late Thursday, which could enhance shower activity Thursday
afternoon.

No AIRMETs are in effect at this time. AIRMET Sierra will be
possible late tonight into Thursday for windward and mountain
areas as a band of moisture moves in. A subtropical jet passing
just south of the state may bring light to moderate turbulence
between FL300 to FL350 around the Big Island through tonight.

&&

.MARINE...
Moderate to locally fresh trade winds will continue to decline as
a strengthen surface trough north of Kauai weakens the local
pressure gradient. The trough will strengthen and expand over the
islands Thursday night and Friday and linger into the weekend,
disrupting the local winds. A strong disturbance aloft moving
overhead will bring a threat for strong to severe thunderstorms
mainly Friday into Saturday. These thunderstorms will have the
potential to produce dangerous wind gusts, hail, and frequent
lightning. Moderate east to southeast trade winds will gradually
rebuild Sunday or Monday.

A long-lived south swell will affect the islands during the next
several days. Low, long-period forerunners of 19 to 21 seconds
have started to arrive at the local buoys this afternoon and will
build over the area tonight. South shore surf is expected to rise
near, or possibly to, the High Surf Advisory level of 10 feet
during the peak of the swell Thursday afternoon through Friday. We
have held off on issuing an advisory for now but will be watching
the buoys closely tonight. This long-lived swell will gradually
decline Saturday through Monday, with a small pulse of south-
southwest expected to follow early next week.

The current northwest swell will continue to decrease to tiny
conditions tomorrow, followed by a reinforcing short-period
north-northwest swell this weekend. Surf along east facing shores
will be well below May average through much of the week, as local
trade winds remain suppressed into the weekend. Only a small
increase is due Sunday or Monday.

&&

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

&&

$$

DISCUSSION...Powell
AVIATION...Kino
MARINE...Bedal/Wroe