Flash Flood Warning 54, NWS Honolulu, HI

Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
612 AM HST Wed Sep 12 2018

.SYNOPSIS...
Tropical Storm Olivia will move through Maui County this morning,
pass south of Oahu and Kauai through this evening, then move away
to the west. A low aloft north of the islands will move southwest,
passing northwest of Kauai on Thursday. Instability from this low
combined with moisture from Olivia will keep the weather wet through
at least early Friday. A surface high will build far northeast of
the state early next week and drier air will spread west across
the islands over the weekend.

&&

.DISCUSSION...
As of 430 am HST, Olivia's low level circulation was a few miles
off Maui's windward coast. The center of Olivia is expect to move
through Maui in the next couple of hours, ushering in more rain
and winds to not only Maui but the entire county itself. The
movement is west at about 12 mph. So, neighboring Oahu, will also
be affected to an extent.

Looking back during the past 10 hours or so, the winds and rain
picked up considerably, especially Maui County. This has led to a
flood advisory for windward Maui, which is on going. Winds have
been blowing hard with a peak wind of 30 mph and peak gusts of 39
mph at Kahului Airport. The wind gage at Lanai hit 37 mph and a
peak gusts at 52 mph. The winds should start to wind down this
afternoon, trending to moderate to strong speeds tonight.

Maui has been the wettest thus far. Rainfall amounts in the past
12 hours ending at 2 am HST include 3.24 inches at Puu Kukui on
the northeast side of windward Haleakala Maui, and 3.73 inches at
West Wailuaiki. Molokai has been wet as well with Puu Alii coming
in at 1.92 inches. Oahu has been damp confined mainly to the
windward and mountain areas. Manoa Lyon Arboretum was the wettest,
reporting 48 hundredths of an inch.

Although the Big Island has been dropped from the tropical storm
threat, the island remains under a Flash Flood Watch. Daytime
heating under a moist unstable air mass will lead to locally heavy
rains including the slight chance of a thunderstorm this
afternoon.

The approaching upper level low will prolong the unsettled weather
through at least Thursday night. Heavier rains and thunderstorms
are likely to occur from tonight into Thursday as the upper low
draws closer to the islands. The upper low is currently 560 miles
NE of Kauai, and should be 450 miles NE of Kauai this afternoon.
The closest point the low is to the islands will come Thursday
afternoon, about a hundred miles NW of Kauai. With this
assessment, the heavier weather is likely to continue into
Thursday. A Flood Watch remains in effect for all islands through
Thursday night, and could be extended into Friday.

The atmosphere will gradually dry out and stabilize as the
moisture from Olivia and the low aloft move away to the west. This
is likely to occur over the upcoming weekend.

Please see the Hurricane Local Statement (HLSHFO) and Local
Watch/Warning Statement (TCVHFO) on our website for detailed
weather information about Olivia and expected impacts to your
local area. The Central Pacific Hurricane Center also posts the
latest Olivia Forecast Advisory tracks at weather.gov/cphc

&&

.AVIATION...
Tropical Storm Olivia continues to move westward around 7 MPH
just 70 miles east-northeast of Maui this morning. Rain bands
associated with Olivia continue to produce moderate to heavy
showers across much of the state. IFR conditions are forecast
across Maui, Molokai and Lanai this morning. MVFR conditions are
forecast over windward and mountain slopes of Kauai and Oahu
through the day. Expect less coverage of low cloud ceilings and
showers over the Big Island today with MVFR ceilings moving in
later this evening. Frequent showers are favoring windward and
mountain areas with scattered to numerous showers over leeward
sections. Wind speeds will continue increasing through the day
with wind gusts already reported over Lanai (PHNY) at 45 KTS this
morning. Isolated thunderstorms are possible today as Olivia
moves through the island chain.

AIRMET SIERRA for mountain obscuration was expanded this evening
to include all island mountains and north through east sections.
AIRMET Tango remains in effect for strong winds producing moderate
low level turbulence over and south through west of mountains over
all islands.

SIGMET NOVEMBER associated with Tropical Storm Olivia is
currently posted over the Hawaiian Islands.

&&

.MARINE...
As Tropical Storm Olivia begins to directly affect the islands,
winds will be on the increase. For the latest on Olivia, please
monitor the forecast and advisory packages from the Central
Pacific Hurricane Center.

Swell from Olivia has been spreading westward across the state.
Surf has been increasing and has already reached warning levels in
coastal sections of windward Big Island, and is expected to reach
warning levels along east facing shores from Maui to Oahu through
today. A High Surf Warning (HSW) remains in effect for east
facing shores of the Big Island, Maui, Molokai, and Oahu through
the day. Lower surf is expected for east facing shores of Lanai
and Kauai, so a High Surf Advisory (HSA) has been issued for those
areas through the same time period. Surf is expected to decline
fairly rapidly as Olivia exits the local waters.

A small northwest swell is expected to fill in late today and
peak Thursday. A small south swell is likely over the weekend,
with another small northwest swell expected late in the weekend
and early next week.

The morning coastal waters forecast will be delayed as we
incorporate the latest forecast information for Olivia.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Tropical Storm Warning for Oahu-Molokai-Lanai-Kahoolawe-Maui.

Flash Flood Watch through late Thursday night for all Hawaii
islands.

High Surf Warning until 6 PM HST this evening for Oahu South
Shore-Oahu Koolau-Olomana-Molokai-Maui Windward West-Maui
Central Valley-Windward Haleakala-South Big Island-Big Island
North and East.

Wind Advisory until 6 AM HST Thursday for Niihau-Kauai.

High Surf Advisory until 6 PM HST this evening for Kauai
Windward-Lanai Makai.

Tropical Storm Warning for Kauai Leeward Waters-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.

Small Craft Advisory until 6 PM HST this evening for Big Island
Leeward Waters-Big Island Southeast Waters.

Small Craft Advisory until 6 AM HST Thursday for Kauai Northwest
Waters-Kauai Windward Waters.

&&

DISCUSSION...H Lau
AVIATION...Bohlin
MARINE...Kinel