High Surf in Hawaii, June 15 to 17, 2016

Area Forecast Discussion
National Weather Service Honolulu HI
344 AM HST WED JUN 15 2016

.SYNOPSIS...
Breezy trade winds will continue through the rest of this week
before diminishing somewhat during the weekend. Wetter than
normal trade showers will continue into today with the majority
of showers falling over windward areas, while leeward locations
will see passing showers. Shower coverage will lessen this
afternoon and tonight as a drier airmass moves in from the east.
Passing showers will be focused over windward areas with mainly
dry conditions leeward from Thursday through the weekend. Showers
will remain possible each afternoon across the leeward slopes of
the Big Island.

&&

.DISCUSSION...
Showers and even a few thunderstorms remain very active across the
offshore waters well to the south of Kauai early on this Wednesday
morning. Only passing showers are affecting the islands, with
mostly light rainfall amounts recorded during the past several
hours. Rains have been a bit more persistent over Kauai, where
some gauges have measured more than a half inch in the past six
hours. Satellite imagery shows an area of showery cumulus moving
into the western parts of the state, with isolated TCU and CB
associated with the thunderstorms south of the islands. Surface
analysis shows a 1035 mb high centered far north of the state,
driving breezy trade winds over the islands. Aloft, an upper level
trough located several hundred miles west of Kauai is keeping the
atmosphere over the state more unstable than usual, especially
over western sections. Mimic- TPW satellite imagery shows an area
of enhanced moisture moving over western sections of the state,
while a considerably drier airmass is moving west into the Big
Island and extends eastward beyond 150W.

A drier and more stable weather pattern should spread from east to
west across the state today. The upper trough west of Kauai will
drift westward, and the area of moisture currently over the
western sections will move west of the state during the day. The
combination of stabilizing conditions aloft along with a drier
airmass moving in from the east should cause showers to become
less persistent and lighter, and mainly confined to windward areas
from Oahu eastward. Rains will be somewhat heavier and more
persistent on Kauai at least through this morning, with some
improvement likely during the afternoon. Will keep an eye on the
thunderstorms currently south of Kauai, but radar trends suggest
that these should remain over the open waters to the south of
Kauai and Niihau. Some afternoon showers will be possible again
this afternoon on the leeward Big Island slopes, but the chances
for thunder there appear to be too low to mention in the forecast.

For tonight through the remainder of the work week, strong
surface high pressure will remain north of the state, maintaining
breezy trades over the islands. This high is forecast to weaken
slightly during the weekend, with trades lessening a notch as well
but still remaining in the moderate to locally breezy range. Model
consensus shows a generally dry and stable airmass prevailing,
therefore expect passing mostly light showers focused over
windward areas, and mostly clear skies with just isolated showers
leeward.

&&

.AVIATION...
Clouds have cleared a bit across the state since late last night,
enough to warrant the cancellation of AIRMET SIERRA for mtn obsc.
There are more low clouds embedded in the trade wind flow and
these will pass through the islands today. Much of the clouds will
affect mainly windward and mountain areas, providing MVFR ceiling
at times with possible isolated IFR ceiling and VIS. Lee areas
will stay mostly VFR, though passing low clouds carried by the
breezy trade winds may bring brief MVFR ceiling for the smaller
islands.

Breezy trade winds will remain in place today. Hence, AIRMET TANGO
for low level turbulence over and immediately south through west of
the mountains will continue.

&&

.MARINE...
Strong trade winds associated with high pressure centered north of
the state will continue into the weekend. The latest nearshore wave
model guidance reflects these winds and depicts seas as high as 9 to
12 feet across the exposed waters. The roughest conditions will
remain over the channels and typical windier waters, especially
across the Alenuihaha. As a result, the small craft advisory for all
waters due to a combination of winds and seas remains in place.

The latest observations from the Lanai PACIOOS buoy are running
higher than the latest model guidance this morning and continue to
support advisory-level surf. As a result, the high surf advisory for
the south facing shores has been extended today. This source should
begin to ease at some point through the day and will need to be
monitored. This downward trend will be expected along south facing
shores through the remainder of the week and into the weekend. Late
Sunday and through the first half of the upcoming week, a series of
south and south-southwest swells will fill in across the waters and
will translate to small to moderate surf returning along south
facing shores.

Rough surf along east facing shores will continue through the rest
of the week due to a combination of strong onshore winds and an
easterly swell that has become established upstream of the islands
over the past few days. The high surf advisory for the east facing
shores has been extended through Thursday. Trades and surf should
slightly ease over the weekend.

In addition to the winds and seas, a few thunderstorms can't be
ruled out today, especially over the northwest waters around Kauai
this morning. This potential will steadily decrease over the next
few days as the upper low centered just west of Kauai continues to
track away from the region.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST this evening for south facing
shores of all islands.

High Surf Advisory until 6 PM HST Thursday for east facing shores
of all islands.

Small Craft Advisory until 6 AM HST Thursday for all Hawaiian
waters.

&&

DISCUSSION...Jacobson
AVIATION...Hui
MARINE...Gibbs