National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXHW60 PHFO 132004
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
1004 AM HST Sat Apr 13 2024

.SYNOPSIS...
A low pressure system northwest of the Hawaii and a surface
frontal trough moving into the state from the northwest will
produce southerly winds and periods of heavy showers and
thunderstorms for the western islands. The initial threat for
flash flooding with this system is highest for the islands of
Kauai and Niihau from later tonight through Sunday night. These
showers will then decrease in intensity as the front weakens and
moves across the eastern half of the state from Monday through
Tuesday. Improving weather trends will develop after the frontal
trough passes through each island. Light to moderate trade winds
will fill in across the Hawaii region from Wednesday onward with
drying trends forecast for most areas.

&&

.DISCUSSION...
A low pressure system currently centered around 775 miles
northwest of Kauai and its associated front located just west and
northwest of Kauai will begin to approach the state and will
bring the threat of heavy rain over Kauai as early as tonight,
but more likely early Sunday into Sunday afternoon. A Flood Watch
has been issued early this morning and it goes into effect at
midnight tonight.

Starting early Sunday morning as the front approaches Kauai,
breezy southerly winds will be on the increase and will bring an
increase of moisture. Latest model guidance is showing
precipitable water values of around 2.0 inches moving into the
area by mid day Sunday. In the upper levels of the atmosphere, we
do have a shortwave trough digging towards the state, which should
help kick off the heavy showers and isolated thunderstorms. At
this time, although there is enough shear to support stronger
thunderstorms, the main instability seems to be north of the state,
so the threat for severe thunderstorms will remain low. Overall,
this event looks to be a heavy rain event with gusty winds at
times with any thunderstorms. Latest forecast has 3 to 6 inches
of rain with isolated pockets of up to 10 inches for Kauai early
Sunday morning through Sunday night. Due to the recent heavy
rainfall, it will likely not take much to cause flash flooding on
Kauai.

As the frontal boundary gradually progresses eastward on Sunday,
showers will be on the increase for Oahu and parts of Maui County.
The frontal boundary should be weakening as it moves eastward,
thus rainfall amounts should be less than on Kauai. The main
moisture band is expected to reach Oahu Sunday afternoon into the
evening and over Maui County Sunday night into Monday. We are
currently monitoring the threat for flash flooding over on Oahu
and Maui County and a Flood Watch will be possible for these
islands late Sunday into Monday. By the time the frontal boundary
reaches the Big Island late Monday into Tuesday, rainfall amounts
should be much less and is not expected to cause a flash flood
threat on the Big Island at this time. Our typical trade wind
weather should return during the second half of next week.

As far as today, scattered showers and muggy conditions will
continue to linger, especially 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 on the
Big Island, we have mid to upper level clouds that will continue
to linger and we should see afternoon showers develop along the
slopes later today.


&&

.AVIATION...
Light to moderate south to southeast flow will allow development
of afternoon sea breezes and overnight land breezes across many
areas. Clouds and showers will favor south and southeast facing
slopes and coasts, with additional showers developing over
interior and windward areas in the afternoon. Showers and
thunderstorms will increase over the western islands tonight as a
front approaches from the west.

AIRMET Tango remains in effect for moderate upper level
turbulence between FL180 and FL380. These conditions will likely
hold through today.

AIRMET Zulu remains in effect for moderate rime icing in cloud, in
precipitation, between FL230 and FL280 due to layered clouds from
Maui eastward. This AIRMET will likely be needed through today and
tonight.

&&

.MARINE...
Light to moderate southerly winds will prevail over the western
islands today, while moderate to fresh southeast winds hold over
the eastern end of the state. A deep low pressure system to the
distant northwest, will track southeast with the attendant cold
front approaching the western end of the state tonight into
Sunday, ramping up the southeast to south winds into the fresh to
strong range. The front will slowly push southeast through the
islands late Sunday through Monday, before stalling out and slowly
dissipating near the Big Island through Wednesday. Moderate to
fresh south winds will prevail through Monday ahead of the front,
with light to moderate west to northwest winds filling in behind
it. Winds will become rather light by Monday night and continue
through next Wednesday, with moderate trades potentially returning
for the latter part of next week.

North shore surf will remain small through the weekend. Surf will
trend up Sunday night and Monday as a small long-period north-
northwest swell coincides with a more significant pulse of medium-
period northwest swell. Surf could reach low end advisory levels
Monday night and Tuesday, with the swell then on the decline
Wednesday through late next week.

Surf along east facing shores will decline over the weekend, with
only small very small surf expected through the upcoming work
week.

A small, long-period south-southwest swell will hold through the
weekend. A new small, but slightly larger, south swell will give
south shore surf a nice boost Tuesday and Wednesday, with another
southwest swell giving surf another bump for late next week.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flood Watch from late tonight through late Sunday night for
Niihau-Kauai-


&&

$$


DISCUSSION...Kino
AVIATION...Powell
MARINE...Foster