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000
FXHW60 PHFO 121957
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
957 AM HST Fri Apr 12 2024

.SYNOPSIS...
A strong low pressure system northwest of the state brought
intense rain and flooding over Kauai last night. Weather
conditions have improved and should generally improve throughout
the day today. Another trough will move into the area Saturday
night and will linger across the state through early next week.
This trough will bring another round of heavy rain starting over
Kauai Saturday night into Sunday, Oahu and Maui County Sunday
night into Monday and over the Big Island Monday night into
Tuesday. Flooding will be the main concern as this trough moves
through the state. Conditions should improve later in the week
with trades returning during the second half of next week.

&&

.DISCUSSION...
A strong low pressure system northwest of the state brought heavy
rain and numerous thunderstorms over the western end of the state
during the past 12 hours. Rainfall totals over Kauai range
anywhere from 4 to 12 inches of rain with the heavier totals
focused over south and east Kauai.

Earlier this morning, we had a large band of moderate to heavy
rain with embedded thunderstorms over the Kauai Channel and
extending into Oahu.  As the kona low gradually weakens and lifts
further north throughout the day, the instability will also lift
further north. Latest satellite and radar imagery is already
showing signs of a weakening trend with cloud tops warming this
morning. For rest of the day today, we should see weather
conditions generally improving through the day with mainly off and
on showers. The threat for flash flooding has diminished over
Kauai, but due to the ongoing issues, a Flood Watch still remains
in place this morning. The Flood Watch should be cancelled
sometime later today.

For Saturday, scattered showers and muggy conditions will
continue to linger over the western half of the state. Sea breezes
developing during the day should lead to increasing clouds during
the afternoon with scattered showers. Over the eastern half of the
state, mid to upper level clouds will continue to linger
especially over the Big Island. Scattered showers will continue
to ride in with the breezy east to southeast winds with afternoon
showers across the leeward slopes.

Starting Saturday night, a shortwave trough will dig towards the
state and will bring periods of widespread heavy rain across the state.
Flash flooding will once again be a concern over Kauai and with
the abundant rain that they received last night, it will not take
much to create more flooding concerns. So for Kauai, the threat of
heavy rain will begin to increase Saturday night with the
heaviest rain likely during the day Sunday. At this time, the
instability looks to be less than what we saw last night, so the
threat for severe thunderstorms will remain low. But with
precipitable water values increasing to around 2 inches, flash
flooding will be the main concern. A Flood Watch should be
reissued by Saturday morning over Kauai. As the upper level trough
continues to dig towards the state, the threat for heavy rain
will expand towards Oahu and Maui County Sunday night into Monday
and over the Big Island Monday night into Tuesday. Our typical
trade wind weather should return during the second half of next
week as a ridge of high pressure builds north of the state.


&&

.AVIATION...
Moderate to locally breezy SE winds over the island chain will
gradually trend down over the next couple of days. Widespread
MVFR/IFR conditions in low clouds and showers are expected for
Oahu today, along with isolated thunderstorms. Conditions will
improve over Kauai today as showers taper down. Elsewhere, expect
mainly limited windward and mauka showers along E/SE slopes, with
VFR conditions prevailing. Conditions are expected to improve over
Oahu later this evening, while showers pick up again over Kauai,
as this system retreats back westward through tonight.

AIRMET Sierra remains in effect for mountain obscuration over
Kauai, Oahu and the Big Island.

AIRMET Tango remains in effect for tempo moderate turbulence
between 080 and FL180.

AIRMET Zulu remains in effect for light icing, as thick mid- and
upper-level clouds continue to stream over the islands from the
southwest.

&&

.MARINE...
A deep surface low centered about 675 nm northwest of Kauai will
drift slowly northeast through tonight, then move slowly toward
the southeast and weaken Saturday and Sunday. The threat of severe
thunderstorms around Kauai has diminished this morning, but
isolated strong thunderstorms with gusty winds will still be
possible as far east as Oahu today. The low and broad high
pressure to the east are producing mainly fresh to strong
southeast across local waters, though winds are more easterly
around the Big Island and slightly weaker around Kauai. As the low
drifts northeastward tonight, expect local winds to ease slightly
and veer out of the southeast to south, and the Small Craft
Advisory (SCA) that currently covers most waters from Oahu to the
Big Island will be limited to waters around the Big Island and
Maui or dropped entirely. For Saturday and Sunday, moderate to
fresh southeast to south winds will prevail, and another round of
heavy showers will develop around Kauai late Saturday and push
east to Oahu late Sunday.

The low will weaken considerably as it passes north then northeast
of the state Monday and Tuesday. A weak trough will move down the
island chain, bringing moderate west to northwest winds and
pushing a band of rainfall over the eastern half of the state.

Small surf will persist across north facing shores through the
weekend with background energy from the northwest and north
expected. An upward trend is expected late Sunday as the arrival
of a small long-period north-northwest swell coincides with a more
significant pulse of medium-period northwest swell from the
nearby surface low. Surf could reach low end High Surf advisory
levels Monday night through Tuesday night. The swell will decline
late Wednesday and Thursday as it shifts out of the north-
northwest.

Surf along east facing shores will decline over the weekend as
locally strong winds trend down and veer out of the south. Small
surf will persist next week.

A small, long-period south-southwest swell should arrive tonight
and hold through the weekend, but southerly winds will lead to
choppy conditions along southerly exposures. Surf along south
facing shores will be small for most of next week.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 6 PM HST this evening for Niihau-Kauai-

Wind Advisory until 6 PM HST this evening for Big Island Summits.

Winter Weather Advisory until 6 PM HST this evening for Big
Island Summits.

Small Craft Advisory until 6 PM HST this evening for Oahu
Windward Waters-Kaiwi Channel-Maui County Windward Waters-Maui
County Leeward Waters-Pailolo Channel-Alenuihaha Channel-Big
Island Windward Waters-Big Island Leeward Waters-Big Island
Southeast Waters.


&&

$$


DISCUSSION...Kino
AVIATION...TS
MARINE...Wroe