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Hawaiian Islands Synoptic Discussion and Guidance

273
FXHW60 PHFO 170641
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
841 PM HST Wed Oct 16 2019

.SYNOPSIS...
Wet weather will continue into Thursday morning over Kauai and
Oahu while passing windward showers are expected over the rest of
the state. Breezy trade wind weather will take over Thursday
afternoon before another boost of moisture increases humidity and
windward showers over the weekend.

&&

.DISCUSSION...
A Flash Flood Watch continues for Kauai and Oahu until early
Thursday morning as moisture from a frontal boundary, and an
upper level low brings unstable atmospheric conditions. By
Thursday morning the moisture from the front is expected to push
west of the state, along with the upper level low, alleviating
the threat of widespread heavy rain. High pressure far north of
the state will maintain trade winds throughout the week and shower
coverage will focus over windward and mountain areas with a few
showers reaching leeward areas.

On Saturday, a weakening front over the Northwest Hawaiian Islands
may push the high pressure generating our trades far enough east
to shift the trade winds from the east-southeast. This slight
shift in wind direction may be enough to allow some tropical
moisture to flow over the eastern half of the state Saturday
afternoon and Sunday. This would increase humidity and trade wind
showers mainly for the Big Island and Maui County. Otherwise,
breezy trade wind weather is expected through early next week as
the high far to the northeast re-establishes itself as our
dominant weather factor.

&&

.AVIATION...
Upper level low moving west of the state tonight will continue to
advect enhanced moisture and instability over Oahu and Kauai.
MVFR conditions could develop due to any passing storms or +SHRA.
For the remaining islands, moderate easterly trades will push a
majority of the SHRA activity against the windward coasts and
slopes.

AIRMET SIERRA remains in effect for Kauai for areas above 2500
feet due to tempo mountain obscuration from low clouds and SHRA.

&&

.MARINE...
A strong high north of the area will maintain locally strong
easterly trade winds over the coastal waters through Friday, and
possibly longer. A Small Craft Advisory (SCA) remains in effect
for Maalaea Bay and the Pailolo and Alenuihaha Channels. We have
expanded the SCA to include the waters south of the Big Island
and extended it through Friday morning. The SCA may need to be
expanded further and extended into the weekend. Winds are forecast
to weaken starting Saturday as the high moves farther east and a
front approaches from the northwest.

A low aloft and moisture from the remnants of a front will
maintain a slight chance of thunderstorms through tonight, mainly
around Kauai and Oahu. The low is forecast to move away tomorrow,
and end the threat of thunderstorms.

Surf is expected to remain below advisory levels along all shores
through early next week. A series of northwest, north, and south
swells will produce small surf through early next week. Surf along
east facing shores will rise a bit over the next few days as the
trades strengthen.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch until 6 AM HST Thursday for Niihau-Kauai-Oahu.

Small Craft Advisory until 6 AM HST Thursday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel- and the waters south of the
Big Island.

&&

$$

DISCUSSION...Morrison
AVIATION...Thomas
MARINE...Donaldson

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