Flash Flood Warning 25, NWS Honolulu, HI

236 
WGHW70 PHFO 312335
FFSHFO

Flash Flood Statement
National Weather Service Honolulu HI
135 PM HST SAT MAR 31 2018

HIC003-312344-
/O.CAN.PHFO.FF.W.0025.000000T0000Z-180401T0130Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Honolulu HI-
135 PM HST SAT MAR 31 2018

...THE FLASH FLOOD WARNING FOR THE ISLAND OF OAHU IN HONOLULU COUNTY
IS CANCELLED...

Weather radar showed that heavy rain has diminished across Oahu.

LAT...LON 2166 15792 2163 15793 2153 15784 2147 15784
      2143 15779 2129 15784 2130 15788 2134 15790
      2130 15791 2130 15794 2134 15797 2131 15801
      2130 15812 2170 15802 2171 15800

$$

Wroe

Area Forecast Discussion
National Weather Service Honolulu HI
948 AM HST Sat Mar 31 2018

.SYNOPSIS...
Mostly cloudy, hazy, and somewhat humid conditions under light
southerly winds will persist over most of the state this weekend.
A front stalling near Kauai will produce wet weather with a few
heavy showers and thunderstorms over the western half of the
state, while the eastern half of the island chain experiences
spotty rainfall. The unusual early April run of hazy and somewhat
humid kona winds will extend into the first half of the work week,
with periods of wet and unsettled weather expected mainly from
Kauai to Maui. On Thursday, a cold front will sweep down the
island chain, spreading showers across each island through early
Friday.

&&

.DISCUSSION...
A front approaching Kauai will produce wet conditions over the
western half of the state today, while a cloudy, hazy and
somewhat humid southeast to south low level flow sets up state-
wide. The ragged front was re-energized overnight by a digging
upper level trough currently centered over Kauai. This feature
has been producing isolated thunderstorms near Kauai and is
rapidly enhancing showers between Kauai and Oahu. Issued an
update to expand thunderstorm chances from Kauai to cover Oahu and
parts of Maui County. Although there could be a brief thunderstorm
on Maui this afternoon, the eastern half of the state will likely
experience spotty shower activity over interior sections.

Chances for showers and thunderstorms will drop off dramatically
during the evening as the weakening upper trough swings east of
the state. Deeper moisture along the ragged front is expected to
stall northwest of Kauai, and as upper level forcing diminishes,
shower activity is expected decrease, with the highest rainfall
chances near Kauai. The somewhat humid southeast to south low
level flow will hold, leading to light land breezes. While the
thick mid to upper level clouds will move off to the east, another
batch of high clouds will be moving in from the northwest later
tonight.

Mostly cloudy, hazy, and somewhat humid conditions will dominate
on Sunday, as the state stays under light southeast to south
winds. With the front remaining stalled northwest of Kauai, the
deepest moisture will remain over the western end of the state.
While spotty showers are expected to develop over all islands
during the afternoon, the greatest chances for rainfall remain
near Kauai. Conditions will remain slightly unstable with no
inversion, but thunderstorms do not appear likely at this time.

Monday through Wednesday, we remain in another interesting
weather pattern for next week with a stationary frontal boundary
lingering just northwest of the islands and a combination Polar
and Subtropical Jet streams aloft. A second low pressure system
will move across the Central Pacific on Monday and Tuesday with
upper level forcing along the stationary front causing a low
pressure system to develop just west of the islands. The pressure
gradients and wind directions will veer towards the south and
southwest in response to this developing low. The low center will
track northeastward brushing past Kauai on Tuesday evening
increasing shower activity across the islands through Wednesday as
it passes. This unusual and complicated weather pattern brings
some uncertainty in the onset timing of rain showers for each
island. We will likely make additional adjustments to the
precipitation chances, intensity and timing as the forecast time
period gets closer. That said, Kauai and Oahu will likely see the
highest shower activity with heavy rainfall and a potential threat
for flash flooding from Tuesday into Wednesday as the low
pressure system passes through the region. A flash flood watch may
be needed for this time period.

On Thursday and Friday, colder air moving into the Central
Pacific from the northwest will help to push this stalled front
through the islands in the latter half of the week. Extensive
clouds and numerous showers are expected for areas within the
frontal band. The latest model projections show the cold front
passing through Kauai early Thursday morning, reaching Oahu by
late morning, passing through Maui County from Thursday afternoon
to evening, and stalling out once again near the Big Island on
Friday.

Meanwhile, a high pressure center moves eastward across the
Central Pacific bringing a brief period of drier and more stable
air to the northern half of the state. Long range forecast
guidance continues to hint that the shifting ridge pattern may
drive the stalled front back towards the central and northern
islands next weekend. Stay tuned for updates and keep watching for
the latest forecast changes on your favorite local TV station or
from our website at weather.gov/hawaii

&&

.AVIATION...
VFR conditions prevail at all TAF sites but brief MVFR conditions
are possible over PHLI...PHNL and PHJR today in SHRA/TSRA.

Airmet Sierra is posted for mountain obscuration over Kauai and
may need to be expanded to Oahu later this morning or this
afternoon.

Airmet Zulu is posted from Kauai to Maui for tempo light icing
between FL150 and FL250.

&&

.MARINE...
The current west-northwest swell is producing low end advisory
surf for north and west facing shores of the smaller islands this
morning, so the High Surf Advisory continues for those shores. The
swell is expected to gradually trend downward tonight through
Monday.

Light to moderate winds are expected to continue over the next
couple of days, along with seas below 10 ft. As such, no Small
Craft Advisories are anticipated.

A front approaching from the northwest is bringing showers, some
with heavy rain, and isolated thunderstorms to the western half
of the island chain and surrounding waters today. Lightning and
sudden wind gusts are possible near the heavy showers and
thunderstorms.

See the latest Oahu Surf Discussion (SRDHFO) for additional
details on surf and swell.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST this evening for north and west
facing shores of Niihau, Kauai, Oahu, and Molokai, and for north
facing shores of Maui.

&&

DISCUSSION...Wroe/Bohlin
AVIATION...Burke
MARINE...M Ballard