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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 010151

Area Forecast Discussion
National Weather Service Honolulu HI
351 PM HST Sun May 31 2020

.SYNOPSIS...The current moderate to locally breezy trades will
decrease over the next few days, while showers begin to increase
as moisture from an old frontal band rides in with the weakening
trades. During the second half of the week, we should see the
return of breezy trade wind weather with scattered showers
focused over windward and mauka areas and generally dry weather
expected over most leeward locations.


High pressure north of the state is currently producing moderate
to locally breezy trade winds across the state. Rainfall totals
have been almost non existent over the past 6 hours with most
gauges with the exception of leeward Big Island reporting no
precipitation. Latest satellite imagery is showing some scattered
cumulus clouds upstream of Maui County and the Big Island this
afternoon. These clouds will be moving in this evening and will
likely produce some scattered light to moderate showers overnight

As the high north of the state begins to shift northeast tonight,
this will result in the trades gradually decreasing through
Tuesday. Winds may briefly become light enough for sea breezes mid
day Tuesday for select leeward areas, but it should be short-
lived as the high northeast of the state strengthens. As the
trades weaken, moisture from an old frontal boundary will move in
and should produce off and on showers over windward and mauka
areas Monday night through Tuesday night. Leeward areas could see
a few passing showers, mainly during the overnight and early
morning hours. Additionally, the combination of lighter winds and
an increase in low-level moisture, will likely make temperatures
feel slightly warmer than normal during the next few days.

During the second half of the week, we will see a new high
building north of the state Wednesday, which will bring the return
of locally breezy trades by Wednesday afternoon. We should see
typical summertime weather with breezy trade winds and light to
moderate showers focused over windward and mauka areas through the


Moderate to locally strong trade winds will persist through
twenty-four hours and beyond. Diurnal wind increases this afternoon
have resulted in gusts over 30 kt over summits and through channeled
areas of the Big Island and Maui. Surface wind speeds should ease
after sunset. AIRMET Tango remains in effect for the lee side of
the mountain ranges of Maui Molokai Lanai and the Big Island
through 04z and is likely to be extended through early evening.

The air mass over the state remains mostly dry and mostly stable.
Shower activity will be limited and focused mainly along Windward
slopes and coasts. Multiple bands of showers embedded in the trade
wind flow can be seen on satellite imagery upstream of the
islands. The next band of showers is expected to reach the
northeast exposures of the Big Island and Maui around midnight.

Light sea breezes along the Leeward Big Island coast will taper
off after sunset, but will likely redevelop Monday afternoon. Weak
land breezes will encourage partial clearing across Leeward
portions of the Big Island after midnight.

Brief MVFR CIG and VIS are possible in isolated moderate showers.
Otherwise, VFR conditions will prevail all areas.


High pressure north of the state is providing for moderate to
locally windy trade winds across the area. A Small Craft Advisory
(SCA) is currently posted for the Alenuihaha Channel as an
daytime ASCAT pass indicated 25 kt winds there. The SCA will
remain up through tonight. The high is forecast to move off to a
position far northeast of the area on Monday resulting in a slight
decrease in trade wind speeds. The high is then forecast to build
back in to our north on Wednesday with trade winds increasing
once again.

Surf along south facing shores will remain slightly elevated
through Monday as a series of southerly swells move through the
area. A larger and longer period south swell is expected to fill
in Monday night, peak during the late Tuesday through Wednesday
time period, then lower gradually Thursday through Friday. A High
Surf Advisory is likely along south facing shores of all islands.
A smaller long period south swell is expected to arrive by next

A series of small north and northwest swells are on tap through
most of the week keeping surf above summertime flatness levels.
With the expected decrease in trade winds across the area, surf
will remain on the small side along east facing shores until the
trades pick up during the second half of the week.


Small Craft Advisory until 6 AM HST Monday for Alenuihaha




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

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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
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