Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 240206
AFDHFO

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

.SYNOPSIS...
Darby will bring stormy weather at times this weekend as it
tracks northwest, close to the Aloha State. More settled weather
will return on Monday as Darby departs, leaving us in very warm
and humid southeast flow for a couple of days. Much more pleasant
tradewind weather is expected to return for the latter half of the
week, as high pressure strengthens far northeast of the islands.

&&

.DISCUSSION...
Per the Tropical Cyclone Update from CPHC, the second tropical
cyclone landfall on the Big Island in three years occurred at
about 2 pm this afternoon, roughly 10 miles east-northeast of
Pahala.

The moist circulation of Tropical Storm Darby interacting
with the Big Island terrain resulted in a considerable amount of
wind acceleration today in some spots, with several wind gauges
recording wind gusts in excess of 50 mph. As the core of Darby
interacts with the Big Island terrain, deep convection has been
blowing up over and near the Kau district over the past few hours.
That will continue to be the concern overnight, with additional
heavy downpours or thunderstorms possible over the Big Island and
then later for Maui county as Darby drags northwest. The
confidence is certainly lower about how much of this moisture will
make it to Oahu on Sunday and Sunday night, but it seems prudent
to leave the Flash Flood Watch in effect until we have a better
idea of how much of Darby will survive the trek across Mauna Loa.

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

Once Darby passes, expect muggy southeasterly flow on Monday.
Thereafter, warm but gradually less humid trade wind weather
should return beginning midweek as Darby moves farther away from
the state and high pressure builds far to the northeast.

&&

.AVIATION...
Darby made landfall this afternoon along the Kau Coast. TC SIGMET
Whiskey series covers all of the Big Island. Within this area, it
will not be unlikely to experience periods of severe turbulence,
icing and low level turbulence, especially in the areas where
convection is the deepest. Convection flaring up along the
southeast coast of the Big Island and the adjacent waters are
carrying CB tops upwards of 55 thousand feet. AIRMET Sierra for
IFR conditions remains posted for the eastern half of the Big
Island. This will likely remain for the next several hours as
Darby moves WNW. Winds at PHTO have veered out of the southeast.

Elsewhere, AIRMET Sierra for mountain obscurations is posted for
Maui, Molokai, Oahu, and western Big Island and will likely need
to expand to Kauai tonight. Conditions over Maui and Molokai have
improved slightly since earlier today and the IFR AIRMET was
replaced with a mountain obscuration AIRMET. Prevailing MVFR is
still expected for most areas into this evening. Conditions may
deteriorate again tonight as Darby is expected to pass south of
Maui County tonight. Expect windward Oahu to remain engulfed in
MVFR conditions tonight and the chance for more prolonged periods
of IFR to increase tonight. 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 Darby over the Big Island,
spreading to Maui tonight.

&&

.MARINE...
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 Oahu-Molokai-Lanai-Kahoolawe-Maui-Big
Island.

Flash Flood Watch from 6 PM HST this evening through late Sunday
night for Oahu.

Tropical Storm Watch for Niihau-Kauai.

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

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

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

Tropical Storm Warning for Kauai Channel-Oahu Windward Waters-
Oahu Leeward Waters-Kaiwi Channel-Maui County Windward Waters-
Maui County Leeward Waters-Maalaea Bay-Pailolo Channel-
Alenuihaha Channel-Big Island Windward Waters-Big Island Leeward
Waters-Big Island Southeast Waters.

Tropical Storm Watch for Kauai Northwest Waters-Kauai Windward
Waters-Kauai Leeward Waters.

&&

$$
Discussion/Marine...R Ballard
Aviation...Eaton



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