Flash Flood Warning 18, NWS Honolulu, HI

Area Forecast Discussion
National Weather Service Honolulu HI
402 PM HST TUE SEP 13 2016

.SYNOPSIS...
Muggy, wet conditions will continue through the week as deep
tropical moisture and an upper level trough affect island weather.
Drier air and a more typical trade wind regime will return over
the weekend.

&&

.DISCUSSION...
Humid conditions with occasional downpours will be the norm
through the week, with more intense showers possible from Oahu
through the Big Island into tonight, and then including Kauai on
Wednesday. A surface trough near Maui and the Big Island has
brought light winds and increased instability to the eastern half
of the state, and a Flash Flood Watch has been expanded to include
Oahu as well. Kauai remains outside the flash flood threat area
with light/moderate trade winds and moderate amounts of moisture,
for now.

The aforementioned surface trough will allow for widespread sea
breezes over Maui and the Big Island again on Wednesday. The seabreezes
and daytime heating will allow increased showers and the chance
for afternoon convection and thunderstorms along the mid- upper
slopes. Locally heavy rains with embedded thunderstorms will be possible.

The MIMIC satellite product (estimated atmospheric precipitable
water) shows values deep tropical moisture from the Big Island to
Oahu with Kauai still in a drier airmass. This swath of moisture
is moving slowly southwest, and is expected to reach Kauai
Wednesday. This moisture will maintain high dew points and very
humid conditions through the week.

A tropical upper tropospheric trough, or TUTT, extends over the
state from the northeast. The TUTT has brought some instability to
the upper atmosphere, allowing for increased coverage and
intensity of showers as well as the chance for thunderstorms over
the eastern half of the state. The TUTT will linger through the
week, coinciding with the presence of the enhanced low level
moisture. The combination of the two will continue our wet and
humid weather, with the potential for locally heavy rain and
isolated thunderstorms through the week.

The low level moisture and upper level trough will move out to the
west Sunday, and high pressure from the northeast will bring back
a dry trade weather regime.

&&

.AVIATION...
A surface and upper trough over the state will bring intermittent
heavy showers and isolated thunderstorms over the next couple of
days. Some heavy downpours will lead to tempo mountain
obscurations, and potentially brief IFR conditions and icing.
Somewhat drier conditions should prevail over Kauai this evening
with the more active weather spreading west by Wednesday.

AIRMET SIERRA remains in effect for tempo mountain obscurations
across most of Oahu, Maui County and the Big Island due to the
cloud cover associated with the showers and thunderstorms. See
WA0HI on our website for the most up to date information. AIRMET
SIERRA will likely be in effect for a least some portions of the
state over the next couple of days. AIRMET ZULU is also in effect
for portions of Maui County and the Big Island for light icing
mainly for areas within and near the heavy showers and
thunderstorms.

&&

.MARINE...
A pair of moderate NW swells are expected through this weekend,
one which is arriving now and expected to peak overnight, with the
second arriving Friday and peaking Saturday. Both swells are
expected to result in surf heights below advisory levels along N
and W facing shores, with open ocean swell heights peaking at 5 to
6 feet in exposed waters. Small swells arriving from the southern
hemisphere will maintain small to moderate surf along S facing
shores the next couple of days, with largest surf expected around
Thursday. The Oahu Surf Discussion (SRDHFO) has additional information
regarding surf and swell affecting the islands.

While sustained winds and seas are below Small Craft Advisory
(SCA) criteria, increasing trade winds are expected toward the
end of the week, as high pressure to the distant NE moves a
little closer, and the surface trough currently near Maui and the
Big Island dissipates. Winds may become sufficiently strong to
support the issuance of a SCA for waters around Maui and the Big
Island at that time.

The island atmosphere is moist and unstable now, and is expected
to remain that way the next couple of days. Heavy showers and
thunderstorms will bring marine hazards in the form of cloud-to-
surface lightning, low visibility, and locally erratic winds.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Thursday afternoon for Oahu-Molokai-
Lanai-Kahoolawe-Maui-Big Island.

&&

Morrison...Discussion
Foster...Aviation
Birchard...Marine

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HONOLULU HI
139 PM HST TUE SEP 13 2016

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0105 PM     FLOOD            WAIHEE                  20.93N 156.51W
09/13/2016                   MAUI               HI   EMERGENCY MNGR

            MAUI COUNTY CIVIL DEFENSE REPORTED PONDING OF WATER ON
            KAHEKILI HIGHWY NEAR WAIHEE SCHOOL

0105 PM     HEAVY RAIN       PUKALANI                20.84N 156.34W
09/13/2016  U0.00 INCH       MAUI               HI   EMERGENCY MNGR

            MAUI COUNTY CIVIL DEFENSE OFFICIAL REPORTED VERY HEAVY
            RAIN

0110 PM     FLASH FLOOD      PUKALANI                20.84N 156.34W
09/13/2016                   MAUI               HI   PUBLIC

            PUBLIC REPORTED FLASH FLOODING FROM RISING STREAM WATERS
            THAT WAS THREATENING HOMES

&&

BIRCHARD