083
FXHW60 PHFO 070649
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
849 PM HST Mon May 6 2024

.SYNOPSIS...
A low pressure system moving into the Central Pacific basin north
of Hawaii will weaken the subtropical ridge and keep light to
moderate trade winds in the forecast this week. An unstable
environment will enhance shower activity across the Hawaii region
through the weekend with the highest rainfall amounts favoring the
windward and mountain areas. A developing upper level low may
produce heavy showers with the potential for thunderstorms over
some islands from Friday through Sunday.

&&

.DISCUSSION...
The upper level low will continue to drift east away from the
islands this evening. Enough upper level troughing will continue
to produce enhanced trade wind showers through Tuesday. A low
level cloud band, the remnants of an old East Pacific cold front,
will drift through the islands on Thursday as an upper level
trough moves in from the north. The surface cloud band and the
upper level forcing from the approaching trough will produce
increasing wet weather trends across the state from Thursday
onward.

A weakening subtropical ridge north of the islands this week will
keep light to moderate trade winds in the forecast through at
least Sunday. A hybrid sea breeze and trade wind pattern will
develop along terrain sheltered leeward areas. The wind pattern
changes again by this weekend as an upper level low sets up
directly over the islands producing a surface trough and light to
moderate southeasterly winds.

An unsettled weather pattern develops over the Hawaiian Islands
in the latest model guidance from Friday through Sunday as an
upper low deepens and stalls over the state. This pattern change
may bring the potential for heavy rain and thunderstorms over some
islands in the state. The potential heavy rain and thunderstorm
impacts will vary greatly depending upon the precise location
where this upper low sets up relative to each island. If the
upper low moves in north and west of the island chain then the
northwest islands of Kauai and Oahu would be under a higher
rainfall threat levels. If the upper low sets up more over the
south and east section of the state, then Maui County and the Big
Island will see higher threats for heavy rain and thunderstorms.
More island by island impacts will be revealed as the time period
gets closer, and the upper low track with weather impacts evolves
over time. Stay tuned.

&&

.AVIATION...
The trades will gradually ease tonight, with moderate trade winds
expected across the island chain on Tuesday. Clouds and showers
will continue to favor windward and mauka areas, with MVFR
cigs/vsbys possible as showers move through. A stray shower may
spill leeward at times, but predominantly VFR conditions are
expected here.

AIRMET Sierra remains in effect for most windward areas and will
likely continue through the night.

&&

.MARINE...
Fresh to strong trade winds will slowly ease through Wednesday as
a 1030 mb high 1000 nm north northeast of the islands moves off
to the northeast. A Small Craft Advisory (SCA) remains in effect
for the typically windy waters around the Big Island and Maui
County, and may be dropped late Tuesday as winds ease to moderate
to locally strong. A surface trough will form north of the state
Wednesday. As this feature drifts southward near or over the
islands Thursday into Saturday, the trade winds could ease
further, and chances for heavy showers will likely increase.

Buoys south of the state and guidance continue to suggest that
the current south swell will remain less than 2 feet at 15 to 17
seconds in the short term, keeping south shore surf below seasonal
average through Tuesday. Forerunners from a larger and longer
lived south-southwest swell will arrive Wednesday, and surf is
expected rise near, or to, the High Surf Advisory level during
the peak of the swell Thursday and Friday. This swell will
gradually decline through the weekend.

A small northwest swell of around 3 feet will continue to build
through tonight, peak Tuesday, then decline Wednesday. Wind-
driven waves of 6 to 7 feet at 8 to 9 seconds will maintain rough
east shore surf above the May average tonight. As trade winds
decline over the next few days, these seas will gradually decline
to around May average by Tuesday, then drop to below average for
the rest of the week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 6 AM HST Tuesday for Big Island Summits.

Small Craft Advisory until 6 PM HST Tuesday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

&&

$$

DISCUSSION...Bohlin
AVIATION...
MARINE...