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Temp5.6 C
RH86 %
WindESE 8 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

787
FXHW60 PHFO 241957
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
957 AM HST WED AUG 24 2016

.SYNOPSIS...
Tropical moisture moving over the state will maintain very humid
conditions with localized heavy downpours and a chance of
thunderstorms through today. Drier trade wind weather will return
from east to west tonight and Thursday, with typical trade wind
weather expected Thursday, and through early next week.

&&

.DISCUSSION...
Deep tropical moisture continues to move over the state from the
east and south bringing uncomfortably humid conditions with the
potential for heavy rain and thunderstorms. Overnight soundings
show very high precipitable water values of 2.3 inches for the
Hilo sounding and 1.8 inches for Lihue. The soundings also show
an unstable atmosphere that has allowed for isolated thunderstorms
across the region overnight with pockets of heavy rain and
flooding.

As of 9am, a band of moisture and showers continues to stream up
from the south over Oahu, Molokai, and Lanai bringing moderate
showers. Thunderstorms have diminished this morning and satellite
imagery shows significant cloud top warming around the islands.
However, daytime heating will provide convective lift to the
already unstable atmosphere, with isolated thunderstorms and
locally heavy rains expected again late this morning, and continuing
through the afternoon. A flash flood watch remains in effect
through 6pm.

A surface trough 500 miles west of Kauai and the associated low
farther north has pushed our normally tradewind- producing high
pressure far into the East Pacific. This in turn, has weakened the
pressure gradient over the islands and turned winds from the east
southeast near the Big Island, and southeast near Kauai. The
trough and low will lift north tonight allowing easterly trade
winds to push back over the islands from east to west through
Thursday. The easterly trades will push drier air over the Big
Island this evening, Maui County and Oahu Thursday, and finally
reaching Kauai Thursday evening.

Drier trade wind weather will continue into early next week, as
high pressure remains to our north. Showers will focus over
windward and mountain areas, while leeward locations will see
mostly clear skies. There is potential for another round of humid
weather by the middle of next week with long term model guidance
bringing tropical moisture close to the state.

&&

.AVIATION...
Islands this morning are beginning to quiet down from an active
night. However, another day of unsettled weather is expected as
deep tropical moisture lingers over the state. The surface ridge
has shifted south, allowing for the background flow to be out of
the southeast. With precipitable water /PW/ values being near and
over 2 inches, periods of heavy showers and thunderstorms are
likely to occur, especially as daytime heating takes hold. A
slight chance for thunderstorms remains over the entire state
today. Any thunderstorm can can carry the threat of lightning,
turbulence, and icing. CB tops are expected to reach between
FL350-400 with the some tops as high as FL500.

Thunderstorms continue to flare northeast of Oahu and through the
Kauai Channel along areas of convergence in the southeast flow.
Most terminals this morning are bouncing between VFR and MVFR
conditions as showers pass. The heavier showers and thunderstorms
expected could bring prolonged period of IFR to any of the
terminals. Sugar cane burning on Maui this morning has led to
reports of smoke within the vicinity of PHOG. The PHOG ASOS will
be out of service, likely into the early afternoon, due maintenance
work.

AIRMET SIERRA for mountain obscuration is posted for the eastern
portion of the Big Island this morning and all of Oahu. This will
be expanded as need today.

&&

.MARINE...
High pressure will build well north of the state today and tonight,
with moderate to locally fresh trades building into the eastern
islands tonight, and into the western islands Thursday. As a
result, small craft conditions are expected to develop over the
windier waters around Maui and the Big Island tonight, with winds
remaining at advisory levels here through at least Thursday night
and likely continue into the weekend. Short period trade wind
swell will increase surf a notch along eastern facing shores
Thursday and into the weekend. Otherwise, no significant surf is
expected.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch until 6 PM HST this evening for all Hawaii
islands.

Small Craft Advisory from 6 PM this evening to 6 AM HST Friday
for Maalaea Bay-Pailolo Channel-Alenuihaha Channel.


&&

$$

Morrison...Discussion and Marine
Eaton...Aviation

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office