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Hawaiian Islands Synoptic Discussion and Guidance

567
FXHW60 PHFO 200633
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
833 PM HST Thu May 19 2022

.SYNOPSIS...
Moisture along a weakening front will maintain higher shower
chances for Kauai through tomorrow. The rest of the state will
experience mainly spotty showers under decreasing southeast to
south winds. High clouds will gradually diminish as humid
conditions persist through Friday. Moderate trade winds will build
during the weekend and will hold into next week.

&&

.DISCUSSION...
Radar shows a line of showers moving over Niihau and Kauai this
evening, but the heaviest rainfall appears to be over the coastal
waters to the southwest and south of Kauai. This will more than
likely bring some additional light to moderate showers to the
Garden Isle over the next few hours.

CIMSS MIMIC satellite derived precipitable water (PW) shows a
swath of moisture from Maui to Kauai between 1.90 and 2.05 inches,
which matches closely to the afternoon sounding from Lihue which
had 2.08 inches.

A stationary front is near the western end of the state and
continues to bring a humid, slightly unstable, and southerly flow
over the islands. The atmosphere is becoming more stable with
time. An upper level trough axis north of the state has swung to
the east, resulting in the high clouds largely clearing the
islands, with further thinning of the high clouds expected
overnight. Dewpoints tonight in the low to mid 70s will keep
humidity values high. Expect some gradual decline in dewpoints in
a couple days.

The moisture band is expected to linger near Kauai through
Friday, with a land and sea breeze regime over the remainder of
the state. Upper level ridging will slowly build in, but a
lingering mid level trough nearby will maintain some instability.
As a result, expect clouds and spotty showers, some briefly
heavy, to develop over most islands in the afternoon and diminish
during the overnight hours. Cloud cover and shower chances will
remain highest over Kauai, with heavier rainfall possible Friday
afternoon. That being said, not expecting any widespread flooding
concerns.

An increasingly stable trade wind flow will build during the
weekend. High pressure far northeast of the state will strengthen,
causing trade winds to slowly increase and push the deeper
moisture west of the state. A mid level ridge will also build
overhead and bring increased stability. The result will be a
return to typical trade wind weather that will hold into next
week.


&&

.AVIATION...

Showery weather will persist statewide, the result of a weak front
stalled over the western end of the state. Low level winds will
be mainly out of the south through the night with deep low level
moisture concentrated over the smaller islands. On Friday, drier
easterly flow will develop over the Big Island and spread across
the remainder of the state by Saturday morning.

The air mass over the state will gradually stabelize as the front
decays. Nevertheless, locally heavy showers are still possible
over Kauai and Oahu, especially in the afternoon and evening hours.
Elsewhere, shower activity should remain light and favor south
and east facing slopes and coasts.

AIRMET Sierra for mountain obscuration remains in effect for
Kauai.



&&

.MARINE...
A front stalled near Kauai this evening will continue to weaken
and drift northward, resulting in a sharp drop in southerly wind
speeds. A high pressure ridge will build back into the region on
Friday with easterly trade winds strengthening from east to west
this weekend. SCA conditions will likely return to the typical
windier waters and channels around Maui County and the Big Island
on Saturday and Sunday. Easterly trade winds with more stable
weather conditions will continue into the middle of next week.

Surf heights along south facing shores will remain elevated into
next week as the current south swell becomes reinforced by
additional long period south swells arriving on Saturday, Monday
and next Thursday. In the long range, models continue to show
quite a bit of activity in the southern hemisphere, which could
translate to additional south shore surf events lasting into early
June.

Surf along north and west facing shores will remain slightly elevated
through tonight as a small, medium-period northwest (300-320 degrees)
swell holds. A return to small, summer-like conditions is expected
over the weekend and into the first half of next week as this
current northwest swell energy fades.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$


DISCUSSION...M Ballard
AVIATION...Bedal
MARINE...Bohlin

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



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