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Hawaiian Islands Synoptic Discussion and Guidance

263
FXHW60 PHFO 281305
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
305 AM HST Tue May 28 2024

.SYNOPSIS...
High pressure to the north will maintain moderate to locally
breezy trade winds through early next week. Showers will favor
windward slopes and coasts, especially during the overnight
and early morning hours. A trough aloft will move over the islands
Friday through early next week, bringing an increase in trade
wind shower coverage and intensity.

&&

.DISCUSSION...
Currently at the surface, a trough of low pressure is located
around 800 miles west-northwest of Kauai, while a 1027 mb high is
centered around 1100 miles north of Honolulu. Moderate to locally
breezy trade winds prevail, strongest over the eastern end of the
state. Infrared satellite imagery shows a mix of high and low
clouds resulting in partly to mostly cloudy conditions. Radar
imagery shows isolated to scattered showers moving into windward
slopes and coasts, with mostly dry conditions in leeward locales.
Main short term focus revolves around rain chances and trade wind
trends.

High pressure will build eastward and strengthen well north of the
state during the next couple days, while the trough of low
pressure remains nearly stationary west of the island chain.
Wind speeds will change little, with the trades holding in the
moderate to locally breezy range. The trough will shift westward
and dampen out Thursday and Friday, with high pressure northeast
of the state then settling southward and closer to the islands
through the weekend. This should give a slight boost to the trade
wind speeds, with moderate to breezy conditions holding in place
through early next week.

As for the remaining weather details, relatively dry trade wind
weather should prevail during the next few days, with showers
favoring windward slopes and coasts particularly at night and
during the early morning hours. Troughing aloft appears to move
over the islands Friday and linger through early next week,
bringing an increase in trade wind shower coverage and intensity.

&&

.AVIATION...
Moderate to breezy trade winds will bring SHRA with periodic MVFR
conds to windward and mauka areas. Otherwise VFR conds will
prevail.

AIRMET Sierra is in effect for mtn obsc for windward Big Island
and N through SE sections of Maui through Kauai.

AIRMET Tango remains in effect for moderate low-level turb
downwind of island terrain. Conds for mod low-level turb look
marginal through the next couple of days and AIRMET Tango may be
needed on and off through the period.

AIRMET Zulu may be needed for light to mod icing around Kauai and
possibly Oahu later this afternoon, due to the low off to the
west.

&&

.MARINE...
Fresh to strong easterly trades will continue through the week as
the surface ridge remains positioned north of the state. The
strongest winds are expected over the windier waters and channels
from Oahu to the Big Island, supporting the Small Craft Advisory
being expanded. The winds over the Kauai waters will fluctuate
between east and east-southeast through Wednesday due to a
persistent surface trough to the west. A shift out of the east-
northeast is expected beginning around Thursday as the trough
weakens and drifts away from the region.

Surf along exposed south-facing shores will remain small
throughout much of the week, due to a combination of background
south-southwest and southeast swell energy. An upward trend is
expected from Friday through the first week of June due to an
active pattern evolving within our swell window near New Zealand.
Altimeter and ASCAT passes over the past couple of days reflected
the potential for the weekend, showing a broad swath of gale-to
storm-force winds with seas up to 30 feet focused at the state
within the 190-200 degree directional bands. This will mark the
beginning of a long-lived event with additional reinforcements
expected within the same area over the next several days.

Surf along exposed east-facing shores will remain small and
choppy throughout the week as the trades persist.

Surf along north-facing shores will remain near the summertime
average each day. Guidance depicts a small, long-period swell
arriving early next week from a gale that is forecasted to track
northeastward today over the far northwest Pacific near the Kuril
Islands.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Wednesday for Kaiwi Channel-
Maui County Windward Waters-Maalaea Bay-Pailolo Channel-
Alenuihaha Channel-Big Island Windward Waters-Big Island Leeward
Waters-Big Island Southeast Waters.

&&

$$

DISCUSSION...Jelsema
AVIATION...Walsh
MARINE...Gibbs

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office