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Hawaiian Islands Synoptic Discussion and Guidance

300
FXHW60 PHFO 280643
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
843 PM HST SAT AUG 27 2016

.SYNOPSIS...
Locally breezy trade winds will continue through early next week as
high pressure persists north of the state. Passing showers will
favor windward and mauka areas, with showers more active tonight
through Sunday night. By the middle of next week, we may begin to
feel impacts from Tropical Storm Madeline, with Hurricane Lester
possibly affecting the islands over the upcoming Labor Day
weekend.

&&

.DISCUSSION...
Currently at the surface, a 1028 mb high is centered around 1650
miles northeast of the state. Meanwhile, Tropical Storm Madeline
is located around 1000 miles east-southeast of the Big Island and
Hurricane Lester is located around 2200 miles east of the Big
Island. Infrared satellite and radar imagery both show a large
area of enhanced clouds and showers upstream of the state and
moving into windward and mauka locales. Main short term concern
for the tonight revolves around rain chances.

Tonight through Sunday night,
High pressure will remain nearly stationary off to the north of
the state, keeping a moderate to locally breezy trade wind flow
in place. Meanwhile Tropical Storm Madeline will continue to
track off to the east-northeast and toward the island chain.
MIMIC total precipitable water imagery shows values between 1.3
and 1.6 inches extending well upstream from the islands, slightly
above climatological norms. Meanwhile, model soundings show
inversion heights remaining elevated through the period due to a
weak mid-level trough moving through the area. As a result, we
should see a wet trade wind pattern through the period with the
brunt of the shower activity focusing across windward and mauka
areas. Due to the elevated inversions and moderate trades,
showers will make it into leeward areas more frequently as well.

Monday through Tuesday,
Deep layered ridging will build to the north of the island chain,
keeping a moderate to locally breezy trade wind flow in place.
Additionally, this will send Tropical Storm Madeline on a more
westward track toward the Aloha state, based on the latest
forecast track from the National Hurricane Center. Both the 00z
ECMWF and 00z GFS show the weak mid-level trough and area of
enhanced moisture sliding southwestward away from the islands
Monday and Monday night, and this should help to lower inversion
heights as well as decrease the coverage of trade wind showers.
Showers will likely increase again by late in the day on Tuesday
as moisture begins to increase in advance of Tropical Storm
Madeline as it approaches the island chain from the east.

Tuesday night through next Saturday,
The medium range portion of the forecast will be highly dependent
on the eventual track and intensity of both Tropical cyclones
Madeline and Lester. The latest forecast from the National
Hurricane center shows Madeline moving over or near the eastern
portion of the island chain in the Wednesday and Wednesday night
time frame. Tropical storm conditions could impact the eastern
portion of the island chain as early as Wednesday afternoon based
on the latest forecast track. Meanwhile, Lester is forecast to
reach 145W Thursday afternoon while tracking eastward toward the
state. Given the uncertainty in the forecast at this time, we will
show wetter than normal conditions through the period and refine
the forecast as details become more clear.

&&

.AVIATION...
Tradewind moisture will affect mainly windward and mountain areas
of the islands occasionally this weekend. Some MVFR ceilings and
visibilities are expected with the clouds and showers passing
through. But overall...VFR conditions will prevail around the
state. Cloud tops are running mostly between 9000 and 11000 feet.
AIRMET SIERRA for mountain obscuration is in effect for north thru
east facing slopes of Kauai Oahu Molokai and Maui. Conditions are
expected to continue through the night.

&&

.MARINE...
A Small Craft Advisory remains in effect for the typically windier
locations around Maui county and the Big Island, due to locally
breezy trade winds accelerating around the island terrain. These
conditions are expected to continue through early next week.
Depending on the eventual track of Tropical Storm Madeline,
Tropical Storm watches may be needed for portions of the marine
area early next week.

No significant swells are expected through the middle of next week,
though surf along east facing shores will be slightly elevated
due to the stronger trades. Winds and seas, as well as surf along
east facing shores, will likely increase toward the middle and
end of next week due to effects from Tropical Cyclones Madeline
and Lester.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Sunday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

&&

$$

DISCUSSION/MARINE...Jelsema
AVIATION...BedaL

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office