High Surf Advisory 41, NWS Honolulu, HI

Area Forecast Discussion
National Weather Service Honolulu HI
359 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...
Stable trade wind weather will dominate through tonight, as
Hurricane Madeline, now centered less than 600 miles to the east
of Hilo, advances toward the state. A relatively strong 1028 mb
surface high will maintain moderate trade winds, while a mid level
ridge keeps the atmosphere rather stable. Moisture within the
trade wind flow will be about 10 to 20 percent below normal
through tonight, keeping modest rainfall focused along windward
slopes.

Rainfall will increase on Tuesday as a broad band of moisture on
the periphery of Hurricane Madeline moves over the islands. Mid
level ridging will maintain stable conditions that will cap the
bulk of the somewhat shallow moisture below 10000 ft. 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.

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 and 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
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.

&&

.AVIATION...
Moderate to locally breezy trade winds will continue through
Tuesday. There are relatively few low clouds within the trade
wind flow immediately in the vicinity of the state to
significantly affect the windward and mountain sections. Only
isolated MVFR ceilings are anticipated through tonight.

Expect some of the showery, broken cumulus along the west periphery
of Madeline to begin moving onto the windward wide of the Big
Island as early as Tuesday morning and onto Maui county toward
midday Tuesday.

Sounding data and cloud top temperatures indicated cloud heights
currently near the islands near 10000 feet but near 12000 feet
around the Big Island.

&&

.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 portions of the island
chain will need to be added to the SCA, if the CPHC track for
Madeline verifies. A Hurricane Watch remains in effect for all
waters surrounding the Big Island, including the Alenuihaha
Channel, where SCA level winds are already present, and additional
waters may 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 on
Tuesday into 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 and Wednesday.

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
east facing shores of Kauai-Oahu-Molokai-and west Maui.

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 East Maui.

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.

&&

Wroe