370
FXHW60 PHFO 210642
AFDHFO

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

.SYNOPSIS...
Moderate to locally breezy trades will hold over the eastern
islands during the next couple days, while lighter trades allow
for some localized land and sea breezes over the western end of
the state. Showers will favor windward and mauka areas overnight
and during the morning hours, with a few showers developing over
interior and leeward sections each afternoon and evening. A more
typical moderate to breezy trade wind pattern will overspread the
state Wednesday night or Thursday and linger through early next
week, with showers favoring windward and mauka areas, along with
the occasional leeward spillover.

&&

.DISCUSSION...
Currently at the surface, a trough of low pressure is located
around 250 miles west-northwest of Kauai, while a 1036 mb high is
centered around 1600 miles north-northeast of Honolulu. Moderate
to locally breezy trade winds prevail over the eastern islands,
while light to moderate trades remain over the western end of the
state. Infrared satellite imagery shows mostly cloudy conditions
in windward areas, and partly cloudy skies in most leeward
locales. Radar imagery shows relatively dry conditions across the
state, with a few showers moving into windward areas, and
dwindling daytime heating showers in some leeward locales. Main
short term focus revolves around rain chances and trade wind
trends during the next couple days.

The trough to the west-northwest of the state will gradually
shift westward and further away from the islands during the next
couple days. This will allow the trade winds to gradually
strengthen from east to west across the islands, with moderate to
breezy conditions expected statewide by Thursday. The gradient
will likely be light enough Tuesday and Wednesday, to allow some
localized leeward sea breezes in the most sheltered areas over
Kauai and Oahu. A series of reinforcing highs will build north of
the state Friday through early next week, while the trough
continues to shift further west and away from the area. This will
maintain moderate to breezy trade winds across the island chain.

As for the remaining weather details, fairly dry conditions should
prevail tonight into Tuesday morning, with light showers limited
mainly to windward slopes and coasts. A band of moisture appears
to move in from the east Tuesday afternoon, bringing an increase
in trade wind showers to the eastern end of the state.
Additionally, a few leeward and interior showers will be possible
over the western islands and leeward Big Island Tuesday afternoon.
Showers should diminish quickly over leeward areas Tuesday
evening, with showers focusing over windward terrain Tuesday night
into Wednesday morning. Localized sea breezes may then allow for
some leeward shower development again Wednesday afternoon.
Beginning Wednesday night or Thursday, we should see a transition
over to a more typical trade wind pattern featuring mainly
windward/mauka showers and the occasional leeward spillover, with
showers most prevalent in the overnight and early morning hours.
This pattern should hold through early next week.

&&

.AVIATION...
Light to moderate east to southeast winds will persist through
the 24-Hr forecast period. Brief periods with MVFR CIGs/VSBYs in
clouds/showers are possible over windward areas overnight through
the morning hours, then over leeward and interior locations
Tuesday afternoon where localized sea breezes form.

AIRMET Sierra is in effect for mountain obscuration over the
windward slopes of the Big Island, and will likely need to be
expanded to Maui later this evening. This could continue into
early Tuesday morning before conditions improve.

&&

.MARINE...
An area of low pressure will linger west to northwest of the
state through much of next week. This low pressure area will
interact with a building high pressure system far northeast of
the state. This weather pattern will produce fresh to locally
strong easterly trade winds over the eastern waters and gentle to
fresh east-southeast winds over western waters through Tuesday.
Easterly trade winds will strengthen over the western waters from
Thursday onward. A Small Craft Advisory (SCA) remains in effect
for the windier coastal waters around Maui County and the Big
Island. The SCA will likely continue for these eastern windier
waters through early next week.

Surf along south-facing shores will continue to gradually
decline over the next several days. Surf heights should continue
to remain above the summer average (5 feet) through Tuesday then
diminish by Wednesday. Only small long period background south
swell pulses are expected from Tasman Sea sources over the next
seven days. Surf along east facing shores should see a gradual
rise over the next few days as the trades strengthen upstream of
the state. Surf heights along north and west facing shores will
remain small with a slight bump up from Sunday into Monday.

&&

.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...Jelsema
AVIATION...Gibbs
MARINE...Bohlin