Heavy Rain in Hawaii, June 14, 2016

Area Forecast Discussion
National Weather Service Honolulu HI
1015 AM HST TUE JUN 14 2016

.SYNOPSIS...
Breezy trade winds will continue through the week before
diminishing over the weekend. Wetter than normal trade showers
will continue through Wednesday with the majority of showers falling
over windward areas, while leeward locations will see passing
showers. Shower coverage will lessen for the second half of the
week as drier air moves in from the east.

&&

.DISCUSSION...
Visible satellite imagery showers two areas of enhanced showers
moving into the islands from the east. The first is already
bringing wet conditions to the windward Big Island with the
leading edge moving into eastern Maui. Showers will increase
through the rest of the morning along windward Haleakala including
the Hana Highway...and then into windward western Maui in the
early afternoon. These showers will continue riding up the island
chain with an expected arrival to windward Oahu late this
afternoon. The second area of showers is pushing toward Kauai
with arrival into the windward Kauai expected by late morning.
Showers will then continue over the windward and mountain areas
of the Garden Isle this afternoon and tonight as those showers
continue to move in from the east.

An upper low centered about 100 miles west of Kauai is responsible
for the aforementioned enhanced showers with cooler temperatures
aloft allowing for higher cloud tops by weakening the normal
trade wind inversion. Near the center of the upper low where
temperatures are coldest, a line of weak thunderstorms have formed
south through southwest of Kauai located about 100 miles offshore.
With the instability remaining over the islands, there is a chance
of afternoon thunderstorms over the Big Island as daytime heating
adds a vertical lift boost at the surface added to the cold air
aloft. With that thunderstorm possibility, the Big Island summits
could see another dusting of snow this afternoon.

Strong high pressure far to the north will continue to provide
breezy trade winds to the Aloha State. The high will remain in
place through the week continuing the breezy trades. A combination
of lingering instability aloft, and enhanced moisture at the
surface will continue to bring enhanced showers to windward areas
and passing showers to leeward areas through wednesday. The upper
low will gradual move west away from the state for the second half
of the week, while drier air is expected at the surface. This
combination will create drier conditions with showers mainly
focused over the windward slopes.

&&

.AVIATION...
Thunderstorm activity this morning remains just south of the
waters adjacent to Kauai, and should continue skirt the coastal
water boundary as it moves west. The upper level low fueling
these storms, will also help to keep a somewhat unstable
atmosphere over the state, with the Big Island being the main
target. A combination of daytime heating with the unstable
atmosphere and increased moisture will lead to the slight chance
for thunderstorm activity to pop- off this afternoon. These
storms will likely carry CB tops to FL350 and numerous TCU with
tops between FL200-250.

AIRMET SIERRA for mountain obscuration is posted over windward
areas of the Big Island. Prevailing MVFR with periods of IFR will
remain likely through most of the day, this includes PHTO, as
patches of enhanced moisture moves through the Big Island. Expect
TCU tops upwards of FL200-250 in these showers. This moisture
will advect west, moving into windward Maui today and Oahu by late
afternoon. Another band of showers will move into Kauai this
afternoon. Some showers will carry MVFR to isol IFR conditions,
with cloud tops near 150 KFT.

AIRMET TANGO for low level turb over and immediately south through
west of the mountains remains posted as trade winds continue to be
elevated.

&&

.MARINE...
Strong trade winds associated with a 1036 MB high pressure centered
north of the state will continue through the week. The latest
nearshore wave model guidance reflects these winds and depicts
seas 8 to 11 feet across the exposed waters. The roughest conditions
will remain over the channels, especially across the Alenuihaha
Channel. As a result, the small craft advisory covers all
Hawaiian coastal waters to account for a combination of winds and
seas.

The latest observations from the Lanai PACIOOS buoy are reflecting the
expected long-period reinforcement from the south. This
reinforcing swell will continue to fill in through the day, and
combined with the current swell, will support advisory-level surf
today and possibly through tonight before easing Wednesday and
Thursday. South shore surf will then steadily ease through the
rest of the week and into the weekend. A small to moderate south
swell is possible early next week.

Rough surf along east facing shores will continue through the week
due to a combination of strong onshore winds and an easterly swell
that has become established upstream of the islands south of the
previously discussed strong high pressure. This energy will likely
translate to a high surf advisory beginning either tonight or
Wednesday for the east facing beaches.

In addition to the winds and seas, a few thunderstorms can't be
ruled out today, especially over the northwest waters around Kauai.
This potential will steadily decrease through mid week as the
instability decreases and the upper low centered nearby tracks
away from the region.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST this evening for Niihau-Kauai
Windward-Kauai Leeward-Oahu South Shore-Waianae Coast-Molokai-
Lanai Makai-Kahoolawe-Maui Leeward West-Maui Central Valley-
Windward Haleakala-Leeward Haleakala-Kona-South Big Island-Big
Island North and East.

Small Craft Advisory until 6 PM HST Wednesday for all Hawaiian
waters-

&&

Morrison...Discussion
Foster...Marine
Eaton...Aviation