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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 280630

Area Forecast Discussion
National Weather Service Honolulu HI
830 PM HST Mon May 27 2024

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 in increase in trade wind
shower coverage and intensity.


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 mostly cloudy conditions. Radar imagery shows
isolated to scattered showers moving into windward slopes and
coasts, with coverage the highest over the Big Island. Leeward
areas are mostly dry, with a few showers over the Big Island. Main
short term focus revolves around rain chances and trade wind

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.
Little change is expected, 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.


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

With a weak shortwave trough passing just northwest of the state
and increased mid level clouds around Kauai, the potential exists
for light icing between 160 and FL250 and light to moderate
turbulence between FL200 and FL340 through tonight.

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

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.


Moderate 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 around Maui
County and the Big Island, supporting the Small Craft Advisory.
The lightest winds are anticipated over the Kauai waters,
fluctuating 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 that has begun 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.


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




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