Flash Flood Warning 27, NWS Honolulu, HI

907 
WGHW70 PHFO 050303
FFSHFO

FLASH FLOOD STATEMENT
NATIONAL WEATHER SERVICE HONOLULU HI
503 PM HST TUE OCT 4 2016

HIC001-050312-
/O.CAN.PHFO.FF.W.0027.000000T0000Z-161005T0415Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
HAWAII HI-
503 PM HST TUE OCT 4 2016

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

WEATHER RADAR SHOWED THAT HEAVY RAIN HAS ENDED.

LAT...LON 1996 15541 1960 15566 1978 15588 2010 15568

$$

FOSTER

Area Forecast Discussion
National Weather Service Honolulu HI
950 AM HST TUE OCT 4 2016

.SYNOPSIS...
An unsettle trade wind pattern will continue through Wednesday,
with the potential for locally heavy rainfall and thunderstorms on
the Big Island. A drier and more stable trade wind weather regime
is expected to return statewide late in the week.

&&

.DISCUSSION...
Water vapor imagery shows an upper level trough just north of the
state slowly lifting to the northeast. A subtropical jet is
located south of the trough and is producing scattered cirrus
clouds across the southern end of the state this morning. At the
low levels, visible satellite is showing clouds mostly
concentrated over the windward sides of the islands, with
southeast portions of Maui and the Big Island also seeing some
cloud cover the morning. Radar has been active with some showers
impacting the windward areas, but much of the activity has waned
over the last two hours. The rest of the state is partly cloudy
to mostly sunny. Moderate east to east southeast winds are driven
by a high pressure system to the northeast and a weak, broad
surface trough over the western end of the state. 12Z soundings
from this morning show precipitable water (PW) values of 1.7 at
Lihue to 2.0 inches at Hilo which is above average for both
locations. MIMIC total PW derived from satellite shows this
moisture fetch will continue to carry in until around Thursday
when the wind direction backs to east northeast.

For this afternoon, we expect the slightly veered winds to allow
sea breezes to build in for some of the more blocked leeward
sections of all islands, though many areas along the windward
coasts will continue to see moderate east winds. The wind flow may
push the vog plume near the smaller islands, but this should be
short-lived. Given the amount of PW over the state, convective and
orographic lift likely in play and the relatively unstable
atmosphere caused by the nearby upper trough, we will have the
potential for locally heavy rain through much of the state and a
chance for thunderstorms for the Big Island this afternoon. Maui
and Big Island look to be the highest threat for flooding given
the higher likelihood of sea breezes setting up and higher
potential moisture to tap into. Thus, a flood watch is in effect
for Maui and the Big Island through Wednesday. Convective snow
showers may be possible on the Big Island summits today into
Wednesday, but given the low probability of impact, we are not
issuing any winter highlights at this time.

Another upper trough will reestablish just to our tonight and
continue the threat for heavy rain into Wednesday. The focus will
shift to windward sides of the islands tonight and Wednesday
morning and back to leeward and interiors Wednesday afternoon.
Showers may linger into Wednesday night and Thursday, but this
will likely be a transition period to drier trade wind type
weather.

By Thursday, trade winds will strengthen over the islands. The
upper trough will slide east of the Big Island by Thursday night
and we will likely see more benign weather from this point into
early next week. A passing disturbance south of the islands early
next week may bring widespread breezy trades to most Hawaiian
waters.

&&

.AVIATION...
The predominant low-level wind flow across the terminals will be
weak and east-southeasterly through the TAF period. This will
allow for some blocking with a diurnal pattern expected at
KHNL/KHJR. With this in mind, clouds and rain showers are expected
to increase in coverage across most of the terminals through the
afternoon. Brief MVFR conditions will be possible with showers. On
the Big Island, thunderstorms will be possible this afternoon at
KHKO. Confidence is not high enough at this time, so will need to
monitor future trends for the possible addition of a TEMPO group
there.

Visible satellite imagery, observations, and radar trends support
the continuation of AIRMET SIERRA. Mountain obscurations are
forecast through the afternoon for the Big Island and the east
the facing slopes of Maui, Molokai, Oahu, and Kauai.

&&

.MARINE...
Winds and seas are forecast to maintain moderate east to
east southeast winds period across the waters as high pressure
weakens to the north and a broad trough becomes established over
the state. Trade winds will gradually come back during the second
half of the week as high pressure strengthens to the north and the
trough weakens.

Surf along east facing shores will maintain over the next couple
of days, rising slightly with the trade winds late in the week.

Elsewhere, generally small surf is expected through Friday with
mainly small background swells from the north and south. Surf
along north and west facing shores will begin to build Friday
night and peak over the weekend at or near advisory level due to a
storm-force low that is currently developing over the northwest
Pacific. The latest WAVEWATCH III is now depicting a slightly
larger northwest swell over the islands compared to previous model
cycles and will need to be monitored over the coming days as this
system evolves. This swell will become reinforced with a similar
northwest (320) swell beginning as early as Sunday night and will
peak through the first half of the upcoming week. This reinforcement
will be in response to Typhoon Chaba recurving and lifting
northeast from Japan to the Aleutian Islands Wednesday night
through Friday.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Wednesday afternoon for Maui-Kona-
South Big Island-Big Island North and East-Kohala-Big Island
Interior.

&&

DISCUSSION/MARINE...Foster
AVIATION...Woodrum