Heavy Rain in Hawaii, March 30, 2022

Area Forecast Discussion
National Weather Service Honolulu HI
943 AM HST Wed Mar 30 2022

.SYNOPSIS...
Light to moderate east to southeast trade winds will continue to
produce rainfall over windward areas today, while sea breezes
trigger clouds and briefly heavy showers over leeward and
interior areas this afternoon. Trade winds build tonight through
Saturday, delivering typical showers to windward areas, while
leeward areas will be mostly dry. Breezy and gusty trade winds may
become strong over the weekend, but will likely diminish again
early next week.

&&

.DISCUSSION...
An unstable east-southeast flow will lead to locally heavy
showers today. An upper level trough is creeping eastward over the
central portion of the state this morning. Thick high clouds have
pushed east of the Big Island, but upper trough will maintain
instability today, especially around the Big Island and Maui.
Light to moderate east-southeast winds will gradually shift more
easterly through the day but will remain weak enough for sea
breezes to take over this afternoon. As a result, expect clouds
and spotty showers, some heavy, to develop over leeward and
interior sections of all islands, with a few thunderstorms flaring
on the Big Island. Windward areas of all islands will continue to
experience scattered showers.

Stability will increase from west to east tonight as trade winds
gradually increase. Some instability will linger and possibly
produce a few heavy showers around the Big Island this evening as
the upper level trough will drift eastward, but otherwise expect
moderate showers to become focused along windward slopes. Easterly
trade winds will slowly strengthen as high pressure builds far
northwest of the state.

Trade winds will build Thursday into Saturday as a typical pattern
of mainly windward rainfall returns. A 1032 mb surface high will
move north of the state by Friday, driving breezy and gusty trade
winds, and as the high drifts closer to the islands on Saturday,
trades will increase further, possibly requiring Wind Advisories
in some areas. Weak mid level ridging will bring back modest
stability, and with little organized low level moisture shown by
the GFS and ECMWF models, expect showers to be focused over
windward areas, along with South Kona slopes during the afternoon
hours.

Trade wind will ease Sunday and Monday as the surface high weakens
and moves off to the east. Another upper level trough may move
over the islands and enhance showers, but confidence in any
increase in rainfall is low.

&&

.AVIATION...
Light to moderate southeast wind will favor a hybrid sea breeze
pattern with emerging sea breezes favoring scattered showers over
inland and leeward areas this afternoon. Though VFR will prevail,
brief MVFR or even IFR will be possible within heavier downpours.
For the Big Island, an approaching upper trough will support
extensive clouds, a higher than normal coverage of interior
showers, and a chance of thunderstorms especially during late
afternoon and early evening. The same trough will bring moderate
upper level turbulence to the eastern end of the state through
today.

AIRMET Tango for moderate upper turb FL280/FL400 will remain in
effect through this afternoon.

&&

.MARINE...
Moderate east-southeast winds will continue today, then shift out
of the east and increase into the fresh to strong category
Thursday as strong high pressure begins to build north of the
area. Winds will peak over the weekend approaching gale force
over the windier waters around Maui County and the Big Island as
the high moves directly north of the state. Seas will respond and
become rough through this time. Small Craft Advisory (SCA)
conditions will be the result across the typical areas Thursday
into Friday, then for all waters over the weekend due to a
combination of winds and seas. Surf along east facing shores will
trend up and become rough Friday through the weekend in response
to the strong trades locally and upstream.

Surf along north and west facing shores will trend down today as a
north northwest swell declines. A new long-period, northwest
swell associated with a large batch of gales that has setup around
1500 to 2000 nm northwest of the islands over the past couple of
days will begin to build down the island chain Thursday night and
peak Friday. Heights may reach advisory levels for exposed north
and west facing shores Friday into Saturday, before easing through
the second half of the weekend.

Surf along south facing shores will remain small through the
weekend with mainly background pulses moving through periodically.
The next pulse is expected over the weekend.

&&

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

&&

DISCUSSION...Wroe
AVIATION...JVC
MARINE...Foster