Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 240930
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
1130 PM HST SAT JUL 23 2016

.SYNOPSIS...
Tropical Storm Darby will bring stormy weather at times during
the rest of this weekend as it tracks northwest over the leeward
waters and passes near the smaller islands. More settled weather
will return on Monday as Darby departs, leaving us in very warm
and humid southeast flow. Much more pleasant trade wind weather
is expected to return beginning Tuesday and continuing for the
second half of the week, as high pressure strengthens far
northeast of the islands.

&&

.DISCUSSION...
Tropical Storm Darby is moving slowly away from the Big Island,
as per the 11 PM HST advisory from the Central Pacific Hurricane
Center. Maximum sustained winds remain near 40 mph, and the
cyclone is moving to the west-northwest at 10 mph.

Recent mesonet reports show the strongest wind gusts currently
occurring over the smaller islands from Oahu to Maui, in areas
where the north/northeast flow around Darby is locally accelerated
by the terrain. The Oahu Forest NWR site high in the Koolau Range
just reported a gust to 60 mph, while a few sites across Maui
County are gusting in the 40-50 mph range. Winds on the Big Island
have generally turned to the south in response to the center of
Darby moving offshore, with Kona Airport reporting southerly
wind gusts to 35 mph earlier this evening. A burst of deep
convection has moved onshore into the Kau district of the Big
Island during the past couple of hours, prompting a flash flood
warning to be issued for that area. Scattered much lighter showers
are present over the other islands, mainly affecting windward
areas.

Overnight and Sunday, Darby is forecast to track to the west-
northwest and northwest over the leeward waters to the south of
Maui County and Oahu. This westward movement should drag the moist
feed of deep tropical moisture located east of the center of
Darby over Maui County late tonight and over Oahu as well on
Sunday. It is impossible to predict the exact evolution of deep
convection within Darby`s circulation during the next 24 hours,
but the potential certainly is there for heavy downpours along
with isolated thunderstorms. The existing flash flood watch
remains in effect for the Big Island and Maui County through
Sunday afternoon, and for Oahu through Sunday night.

Winds will continue to be a secondary threat, but there will
continue to be localized areas of strong winds or gusts in areas
of strong downsloping and acceleration through gaps, as well as
with any deep convective bursts that develop. Not all locations
will see tropical-storm-force winds, but there will likely be
at least some pockets of wind damage associated with Darby.

Once Darby passes, expect muggy southeasterly flow with scattered
showers on Monday. Thereafter, warm but gradually less humid trade
wind weather should return beginning Tuesday as Darby moves
farther away from the state and high pressure builds far to the
northeast. Pleasant and fairly dry trade wind weather should
prevail from Wednesday through the remainder of the week.

&&

.AVIATION...
Darby has moved just west of the Big Island this evening. TC
SIGMET Whiskey series covers all of the Big Island, covering the
potential for severe turbulence and icing with deep convection.
AIRMET SIERRA for IFR conditions remains posted for the the
eastern half of the Big Island, while another AIRMET SIERRA for
mountain obscuration above 2000 feet covers the western half.
These AIRMETS will likely remain in effect through the night.

Elsewhere, AIRMET SIERRA for mountain obscuration remains in
effect for Maui, Molokai, Oahu, and Kauai tonight. Prevailing
MVFR is still expected for most areas tonight. Conditions may
deteriorate later tonight as Darby is expected to pass south of
Maui County. Expect windward Oahu to remain engulfed in MVFR
conditions tonight along with the chance for more prolonged
periods of IFR. Expect PHNL and PHJR terminals to see passing
showers through the night.

AIRMET TANGO remains posted for low level turbulence over and
immediately south through west of the mountains and for strong
surface winds associated with Tropical Storm Darby over the Big
Island, and may have to be expanded to include Maui tonight.

&&

.MARINE...
A tropical storm warning remains in effect for all Hawaiian
coastal waters. Winds and seas are going to continue to be
hazardous in the vicinity of Darby for the rest of the weekend.
The seas will be highest over windward waters where the upstream
fetch was much longer, but should gradually be declining by Sunday
over the Big Island waters. The seas will be climbing near the
smaller islands as Darby starts tracking northwest, though the
island terrain will block the highest seas from reaching shadowed
leeward waters. The high surf headlines for east facing shores
have been extended through Sunday. There will also be pockets of
intense rainfall, very low visibilities, and embedded
thunderstorms with frequent cloud-to-surface lightning associated
with Darby this weekend as it continues toward the west-northwest.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Tropical Storm Warning for all Hawaii islands.

Tropical Storm Warning for all Hawaiian waters.

Flash Flood Watch through late Sunday night for Oahu.

Flash Flood Watch through Sunday afternoon for Molokai-Lanai-
Kahoolawe-Maui-Big Island.

High Surf Warning until 6 PM HST Sunday for east facing shores
of Maui and the Big Island.

High Surf Advisory until 6 PM HST Sunday for east facing shores of
Molokai Oahu and Kauai.

&&

$$

DISCUSSION/MARINE...Jacobson
AVIATION...Powell


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