Winter Storm Warning 1, NWS Honolulu, HI

Area Forecast Discussion
National Weather Service Honolulu HI
839 PM HST Fri Apr 15 2022

.SYNOPSIS...
A transition to a wet trade wind pattern is in store for portions
of the state this weekend as an upper trough settles southward
into the area. Windward and mauka showers will increase in
coverage, with some making it into our dry leeward areas
periodically with the gusty trades in place. The best chance for
heavy showers and even a few thunderstorms that could lead to
localized flooding will be over the eastern end of the state. A
return of drier trade wind conditions is expected early next week.

&&

.DISCUSSION...
Guidance remains in good agreement and depicts a wet pattern
evolving over the state this weekend as upper heights lower in
response to a short wave trough settling southward into the area.
Expect this transition to begin as early late tonight through the
early morning hours Saturday as a decent sized area of higher
moisture lurking east of the Big Island begins to move in.
Showers will become heavy at times, which increases the threat for
localized flooding - in the event of anchoring or where they
become focused over time. Although the best chance for this
threat is over Maui County and the Big Island, a few heavy showers
can't be ruled out across the western end of the state as well -
with some showers spilling over into our dry leeward areas where
drought conditions are occurring. In addition to the rainfall
potential, the added instability and deep moisture also supports
a few thunderstorms. For the Big Island summits, expected a
transition to a wintry mix, with the best shot at this being
Saturday through early Sunday (Winter Weather Advisory or Warning
likely later tonight to cover this potential).

A low will pinch off from the upper trough and move away to the
southwest on Monday, resulting in a transition to a drier and more
stable trade wind weather regime, which will continue through the
at least the middle of the week.

&&

.AVIATION...
High pressure ridge north of the state will maintain moderate to
breezy trade winds throughout the weekend, anchoring a majority of
showers along northeast facing slopes and coasts. Current radar
trends show mainly scattered showers over windward slopes this
evening, however showers are expected to increase in intensity and
areal coverage through Saturday as an upper trough drifts across
the islands.

AIRMET for MVFR cigs and vsby will continue over windward Big
Island toward Maui, with MVFR cigs and vsby and tempo mtn obsc
possibly expanding across neighboring islands later tonight
through Saturday as conditions continue to deteriorate.

AIRMET Tango for low level mechanical turbulence to the lee of
higher terrain remains in effect, and is expected to continue
through Saturday. Additionally, a period for tempo light ice
will increase across the islands from west to east through
Saturday as deeper mid and upper lvl moisture builds in overhead.

&&

.MARINE...
High pressure northwest of the islands will keep moderate to
strong trades in place through the forecast period, with only
minor variations in strength. A Small Craft Advisory (SCA) remains
in effect for the typically windy waters around Maui and the Big
Island through 6 PM Sunday.

Moderate to locally strong trade winds will keep east shore surf
close to seasonal levels through Saturday. Surf will then lower
below normal Sunday through late next week as the trade winds
diminish upstream of the island chain.

South shore surf will trend up tonight, then hold at slightly
above normal levels Saturday through Monday as a new moderate size
south swell moves through. Surf will then lower back to seasonal
levels Tuesday through the end of the work week.

A series of small northwest swells will move through the area
tonight through Monday, maintaining small surf along north facing
shores. A larger, long period northwest swell associated with
former tropical cyclone Malakas, will arrive Monday night and
Tuesday, giving a noticeable boost to surf along north and west
facing shores Wednesday through late next week.

&&

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

&&

DISCUSSION...Gibbs
AVIATION...SWR
MARINE...Jelsema