Area Forecast Discussion
Issued by NWS Honolulu, HI

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729
FXHW60 PHFO 300644
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
844 PM HST MON AUG 29 2016

.SYNOPSIS...
Moderate trade winds will continue through Tuesday as high
pressure persists north of the state. A rather dry airmass is
expected over the islands through tonight, followed by an
increase in moisture on Tuesday. While uncertainty remains with
the forecast track of Hurricane Madeline, direct impacts,
including damaging winds, flooding rain, and high surf, are likely
over portions of the state during the Wednesday through Thursday
time frame. After a brief return of stable trade wind weather,
Hurricane Lester may affect the islands over the upcoming Labor
Day weekend.

&&

.DISCUSSION...
Currently at the surface, Hurricane Madeline is located around
550 miles east of Hilo, while Hurricane Lester is around 1500
miles to the east of the Hilo. Meanwhile, the two weather systems
driving the moderate to locally breezy trade wind flow across the
island chain this evening are a 1027 mb high around 1300 miles
north of the state and Invest 92C around 475 miles south-
southwest of Honolulu. Infrared satellite imagery shows partly
cloudy skies in place in most areas, with some high cloud spilling
northward into Oahu from Invest 92C. Radar imagery shows a few
isolated showers drifting into windward locations and along the
coast of leeward Big Island, with rain free conditions elsewhere.
Main short term concern over the next few days continues to center
around the impacts Madeline will bring to the Aloha state.

Tonight,
High pressure north of the state and Invest 92C to the south will
keep a moderate to breezy trade wind flow in place through the
night. MIMIC total precipitable water (PW) imagery shows a dry
airmass upstream of the island chain, with values between 1.0 and
1.3 inches. This should keep a fairly dry trade wind flow in
place through the night with clouds and showers limited primarily
to windward and mauka locales. Across leeward sections of the Big
Island, the showers are expected to end with in the next hour or
two.

Tuesday and Tuesday night,
Rainfall will increase across the islands through the day as a
broad band of moisture on the periphery of Hurricane Madeline
moves over the islands from east to west. Mid level ridging will
maintain relatively stable conditions, with the bulk of the
moisture below 12 kft. As a result, moderate trade winds will
focus clouds and showers over windward slopes, though some
showers will be carried across leeward areas at times.

Wednesday through Sunday night,
The main concern heading into Wednesday and Thursday will be the
impacts from Hurricane Madeline. The latest track from the
Central Pacific Hurricane Center (CPHC) shows Madeline moving near
the Big Island later Wednesday through Thursday, and a Hurricane
Watch and Flash Flood Watch are in effect for that island. While
the highest chances of damaging winds, flooding rainfall, and
large dangerous surf are on the Big Island, any change in the
track could mean that additional portions of the state will
experience direct impacts and could be placed under a watch or
warning. For this reason, it is important to not focus too closely
on the exact forecast track of Madeline, especially since the
average forecast track error is about 85 to 150 miles in the 48 to
72 hour time range. It is also important to note that significant
impacts can extend well away from the center of a tropical
cyclone. Please refer to the Hurricane Madeline Local Statement
(HLSHFO) for details.

Distant Hurricane Lester may threaten the state during the
Holiday weekend. It is far too early for specifics at this time,
and all islands have roughly equal chances of experiencing direct
impacts from Lester. Residents and visitors are urged to closely
monitor the latest forecasts from the CPHC and NHC regarding these
tropical cyclones.

Next Monday,
Both the 00z GFS and 00z ECMWF are in good agreement showing deep
layered ridging building well north-northeast of the islands. This
should allow a drier and more stable trade airmass to spread from
east to west across the state, bringing a return of more typical
trade wind weather to the Aloha state.

&&

.AVIATION...
VFR conditions will mostly prevail across the terminals through
the TAF period as moderate to locally breezy trade winds will
continue through Tuesday. Windward and mountain areas will see
isolated MVFR ceilings overnight.

The trade wind pattern will continue on Tuesday, but the main
driver for weather across the terminals of the Hawaiian Islands
will begin to shift to Hurricane Madeline as it approaches from
the east. An area of moisture ahead of Madeline may clip the
terminals late in the day on Tuesday into Tuesday night. This will
increase chances of brief MVFR showers across the terminals late
in the TAF period.

&&

.MARINE...
A Small Craft Advisory (SCA) remains in effect for Maalaea Bay
and the Pailolo channel through Thursday night. While there may
be a slight downward trend in winds on Tuesday, winds should pick
up once again Wednesday and Thursday as Hurricane Madeline
approaches from the east, and additional marine zones will likely
need to be added to the SCA. A Hurricane Watch remains in effect
for all waters surrounding the Big Island, including the
Alenuihaha Channel, where SCA level winds are already present.
Additional marine zones may need to be added to the watch tonight
or Tuesday, depending on the track of Madeline.

No significant swells are expected through tonight. Winds and
seas, as well as surf along east facing shores, will increase from
east to west late Tuesday and Tuesday night with the approach of
Madeline. The east swell is expected to peak at warning levels
for east facing shores of the Big Island and east Maui Tuesday
through Thursday. While surf conditions on the Big Island are
covered in the Hurricane Madeline Local Statement (HLSHFO), a High
Surf Warning has been issued for east Maui due to building surf on
Tuesday. The rest of the state will remain partially shadowed from
the bulk of the swell energy from Madeline, and a High Surf
Advisory has been issued for their east facing shores for rising
surf later Tuesday through Thursday.

We will also start to see a long-period swell from Hurricane
Lester beginning Wednesday night or Thursday, with surf building
into the weekend, likely to warning levels along east facing
shores of all islands. In addition, small surf from distant
Typhoon Lionrock will affect the state late Wednesday through
weekend.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Hurricane Watch for Big Island.

High Surf Advisory from 6 PM Tuesday to 6 AM HST Thursday for
Kauai Windward-Oahu Koolau-Olomana-Molokai Windward-Maui
Windward West.

Flash Flood Watch from Wednesday morning through late Thursday
night for Big Island.

High Surf Warning from 6 AM Tuesday to 6 AM HST Thursday for
Windward Haleakala.

Hurricane Watch for Alenuihaha Channel-Big Island Windward
Waters-Big Island Leeward Waters-Big Island Southeast Waters.

Small Craft Advisory until 6 AM HST Friday for Maalaea Bay-
Pailolo Channel.

&&

$$

DISCUSSION/MARINE...Jelsema
AVIATION...Woodrum



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