760
FXHW60 PHFO 130655
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
855 PM HST Sun May 12 2024

.SYNOPSIS...
Light southeasterly winds, afternoon sea breezes and weak
troughing aloft will produce brief periods of slow moving showers
over some islands through Tuesday. Some of these showers may
become heavy at times especially along the eastern slopes of Oahu
and Maui, and the southeastern slopes of the Big Island. On
Wednesday the weather pattern trends more unstable as southerly
winds develop over the state in response to a kona low approaching
the islands from the north. Deep unstable tropical moisture will
move over all islands from the south resulting in periods of heavy
rainfall, thunderstorms and strong gusty winds. The threats from
flooding and thunderstorms will be elevated for all islands from
Wednesday into next weekend.

&&

.DISCUSSION...
The weather pattern for the next few days keeps the Hawaiian
Islands in a light southeasterly wind pattern with land and sea
breezes forming over each island. Forecast guidance and satellite
water vapor imagery continues to show weak upper level troughing
that will enhance some shower activity across the state.
Southeasterly winds tend to produce small scale convergence plumes
in the lee of island mountains and when combined with upper level
instability tend to create enhanced showers over windward Oahu.
Southeasterly flow will also combine with sea breezes to drive
clouds and showers up the mountain slopes of east Maui and the
southeast slopes of the Big Island over the Kau and Puna
districts. Localized slow moving heavy rain may also develop over
some areas and Flood Advisories may be needed mainly in the
afternoon to early evening hours through Tuesday.

Wednesday through Friday...Another unstable weather pattern
develops across the Hawaiian Islands as a unseasonably deep kona
low approaches the islands from the north. A cold front riding in
ahead of this system will help to produce southerly kona winds
over the islands starting early Wednesday morning. These southerly
winds will draw up deep and unstable tropical moisture ahead of
the approaching cold front. The cold front will weaken into a
trough on Thursday as it merges with the tropical moisture plume
right over the islands. Forecast models show both features will
impact all islands during this time period.

Several threats are likely in this weather pattern from Wednesday
onward including heavy rain with flooding, thunderstorms in the
strong to severe range, and strong gusty winds. The severe
thunderstorm threat will favor the western islands closer to the
approaching surface front/trough, the upper level cold pool and
the strongest wind shear. The forecast guidance over the past few
days suggests these threats will last for several days from
Wednesday through Friday and possibly linger into next weekend. A
very wet and unstable pattern for this time of year. Stay tuned.

&&

.AVIATION...
Lingering instability aloft combined with a moist southeasterly
flow will continue allowing a few more heavy showers across the
state through the forecast period, with the slight possibility
remaining for an isolated thunderstorm over the Big Island. The
heaviest showers will mostly be focusing over southeast facing
slopes of each island. Winds will remain light enough to allow
for a land/sea breeze pattern where clouds and showers will build
up over island interiors during the afternoon/early evening hours
and begin to clear out overnight. MVFR conditions are still
expected in any heavier showers, with brief IFR conditions
possible.

AIRMET Sierra for tempo mountain obscuration is in effect over the
the Big Island, Maui, Molokai, Oahu and Kauai. This AIRMET may be
needed on and off into tomorrow morning across portions of the
island chain due to shower activity. AIRMET Sierra for IFR
conditions may also be needed for the southeastern slopes of the
Big Island tomorrow as showers periodically become heavy.

&&

.MARINE...
Moderate to strong east-southeast trade winds will persist
tonight, and a Small Craft Advisory (SCA) is now in effect for
most of the waters around Maui and the Big Island through 6 AM
Monday. Winds will gradually ease Monday and Monday night, then
become more southerly on Tuesday as troughing amplifies to the
west of the state. Moderate southerly winds will develop in
advance of a front Wednesday. The front will move into the
western islands Wednesday night and Thursday, then weaken into a
trough and shift westward Friday. Light to moderate northwest
winds may briefly develop behind the front over the far western
end of the state, otherwise moderate southerly winds should
prevail into next weekend.

Surf along south facing shores will slowly decline through Monday
night. A series of overlapping, long-period south swells will
move through the islands Tuesday into next weekend. This will be
a long lived south shore event, with surf holding well above the
summertime average Wednesday through next weekend.

A small, long-period northwest swell will build tonight, peak on
Monday, and then slowly decline Tuesday, giving north shore surf a
slight boost for a couple days. A series of reinforcing northwest
swells will keep some small to moderate sized surf moving into
north facing shores Wednesday through next weekend.

Surf along east facing shores will remain well below normal
levels through next weekend.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 AM HST Monday for Maui County
Windward Waters-Maui County Leeward Waters-Pailolo Channel-
Alenuihaha Channel-Big Island Windward Waters-Big Island Leeward
Waters-Big Island Southeast Waters.

&&

$$

DISCUSSION...Bohlin
AVIATION...Tsamous
MARINE...Jelsema