Small Craft Advisory 47, NWS Honolulu, HI

Area Forecast Discussion
National Weather Service Honolulu HI
324 AM HST THU SEP 15 2016

.SYNOPSIS...
A very moist and unstable weather pattern will continue as
abundant tropical moisture and an upper trough affect the state.
Heavy showers and thunderstorms will be possible today and
tonight. The threat of heavy rainfall will linger into Friday.
Drier conditions and a more stable airmass will return over the
weekend and early next week.

&&

.DISCUSSION...
Weak surface troughing persists across the main Hawaiian Islands,
pulling abundant tropical moisture northward as fuel for continued
bouts of heavy showers and thunderstorms this morning. A
persistent upper trough directly across the islands continues to
destabilize our airmass. Overnight soundings showed lifted index
values of -5, with CAPE near 2000 j/kg and between 1.6 and 2.0
inches of PW. This combination of abundant moisture and
instability will maintain the threat for flash flooding, and the
Flash Flood Watch has been extended through Friday afternoon for
all islands from Oahu eastward.

The surface trough across the islands is washing out. This feature
slackened the pressure gradient between the subtropical ridge to
our north and equatorial low pressure, keeping trade winds rather
light near the eastern islands over the past few days. Slightly
stronger trades are noted west of the trough axis, mainly across
Kauai and Oahu. The current bout of heavy showers and
thunderstorms over and near Maui and the Big Island lies east of
the sharp upper trough axis, which extends northeastward from
18N161W through 28N150W and 34N140W. Heavy rainfall could spread
west to Molokai and Oahu at any time today through Friday
afternoon.

Models show the area of abundant tropical moisture will move west
of the islands by Saturday afternoon. We expect the upper trough
will pinch off into an upper low and drift west of the islands
this weekend, gradually allowing more stable air to move in from
the east. The subtropical high far to our north will shift
southward today and Friday, allowing trade winds to gradually
strengthen. We should be back in a more traditional trade wind
pattern this weekend and first half of next week.

&&

.AVIATION...
The airmass in the island vicinity remains moist and unstable
today as ample tropical moisture lingers across the islands, while
an upper level trough deepens in the vicinity as well. Thus
localized heavy downpours and isolated thunderstorms are possible
across the area throughout the day.

AIRMET SIERRA for mountain obscuration remains in effect for
portions of Maui and the Big Island early this morning. This is
subject to change as conditions may worsen for other islands later
today.

SIGMET QUEBEC remains in effect for embedded thunderstorms along and
to the southeast of the upper level trough. This SIGMET may need to
be extended if the convection persists.

&&

.MARINE...
A moderate northwest swell is expected to arrive Friday and then
peak on Friday night and Saturday. Surf heights will stay below
advisory levels along north and west facing shores, with open
ocean swell heights peaking at around 5 feet in exposed waters.

Small swells arriving from the southern hemisphere will maintain
small to moderate surf along south facing shores over the next
couple of days, with largest surf expected today. 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 this morning, increasing trade winds are expected
tonight as high pressure to the distant northeast moves a little
closer. An SCA is therefore in effect beginning tonight for the
traditionally windy waters around Maui and the Big Island. This
SCA may need to be expanded to cover additional waters later.

Our airmass is moist and unstable now, and is expected to remain
that way through today and possibly Friday as well. Heavy showers
and thunderstorms will bring marine hazards in the form of cloud-
to-surface lightning, low visibility, and locally erratic winds
across Hawaiian coastal and offshore waters.

&&

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

Small Craft Advisory from 6 PM this evening to 6 PM HST Saturday
for Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island
Leeward Waters-Big Island Southeast Waters.

&&

DISCUSSION/MARINE...Powell
AVIATION...HUI

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HONOLULU HI
1005 PM HST WED SEP 14 2016

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

0900 PM     FLOOD            MOUNTAIN VIEW           19.52N 155.15W
09/14/2016                   HAWAII             HI   EMERGENCY MNGR

            NORTH PECK ROAD CLOSED DUE TO DOWNED TREE

0920 PM     FLOOD            MOUNTAIN VIEW           19.52N 155.15W
09/14/2016                   HAWAII             HI   EMERGENCY MNGR

            SOUTH KOPUA ROAD FLOODED 1.5 MILES FROM HIGHWAY 11.
            TRAFFIC RE-ROUTED THROUGH FARM LOTS.

&&

BIRCHARD