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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 151949

Area Forecast Discussion
National Weather Service Honolulu HI
949 AM HST Mon Jul 15 2019

A trade wind weather pattern can be expected through the remainder
of the week and on through the weekend, thanks to high pressure
far north of the area. Clouds and passing showers will tend to
favor windward and mauka areas. Leeward sections of the Big Island
will see clouds and showers mainly during the afternoon and
evening hours.


At the surface, a 1030 mb high is centered far north of the state.
This places the islands in a moderate to breezy trade wind
environment. Moisture embedded in the trades is providing for
passing light showers for some windward and mauka areas,
primarily over Kauai and Oahu. Expect a slight drying trend as the
day progresses with the exception of leeward Big Island where
daytime heating will likely cause clouds and some showers to form
over the slopes during the afternoon and evening hours. This
general weather pattern is expected through the day Tuesday.

Water vapor imagery along with model guidance shows a broad mid
and upper level trough centered a few hundred miles to the east
northeast of the Big Island. This trough is forecast to drift
westward over the next few days which will likely cause inversion
heights to rise a bit. A small area of enhanced moisture can be
seen on satellite imagery a few hundred miles east of the area.
Guidance indicates that this area of moisture will reach the Big
Island Tuesday afternoon or evening, then pass westward across the
remainder of the state Tuesday night into Wednesday morning. An
uptick in windward and mauka shower activity is expected with this
feature passing through especially for windward and mauka. The
trades will be sufficiently strong enough for some brief passing
showers over some leeward locations.

The surface high to the north is forecast to strengthen during the
middle and latter half of the week. The result will be for an
uptick in trade wind speeds across the area. Also by the middle of
the week, the upper trough will have weakened and moved to a
position just west of the state. Thus a typical windward and mauka
distribution of shower activity is expected and will be highly
dependent on incoming moisture availability.


High pressure north of the state will keep a breezy to locally
windy, easterly trade wind flow in place through tonight.
Relatively dry conditions will prevail with a few light showers
affecting mainly windward and mountain areas. Brief MVFR cigs/vis
are possible as showers move through, but VFR conditions are
expected to prevail statewide over the next 24 hours.

AIRMET Tango remains in effect for moderate, low-level turbulence
over and downwind of the higher terrain of all islands. These
conditions are expected to continue for the next couple of days.


A high far north of Kauai will move east slowly over the next
several days. The pressure gradient south of the high will remain
tight enough to maintain locally strong easterly trade winds over
the Hawaii coastal waters through the week. A Small Craft
Advisory is in effect for the windy areas around the Big Island
and Maui. The advisory may need to be expanded around mid-week.

The large south swell affecting the Hawaii coastal waters is now
subsiding. The High Surf Warning was downgraded and is now a High
Surf Advisory for all south facing shores through tonight. The
swell is aimed just southeast of the coastal waters so surf will
be highest on the Big Island and lowest on Kauai. This swell will
continue to slowly subside through mid-week. The locally strong
trade winds will produce choppy waves along east facing shores but
the fetch will be short for the next couple of days so wave
heights will remain relatively small. Surf along east facing
shores will increase by mid-week as the fetch becomes longer. Only
very small surf is expected along north facing shores through the


High Surf Advisory until 6 AM HST Tuesday for Niihau-Kauai
Windward-Kauai Leeward-Oahu South Shore-Waianae Coast-Molokai
Leeward-Lanai Makai-Kahoolawe-Maui Leeward West-Maui Central
Valley-Windward Haleakala-Leeward Haleakala-Kona-South Big
Island-Big Island North and East.

Small Craft Advisory until 6 AM HST Saturday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.




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

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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
Send comments to: Ryan Lyman