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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 162003

Area Forecast Discussion
National Weather Service Honolulu HI
1003 AM HST Tue Jul 16 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. Satellite imagery shows an area of enhanced moisture
embedded in the trades, which is expected to cause some increase
in shower activity across portions of the state. Some of this
moisture is forecast to move into portions of the state later
today then pass across the area tonight and early Wednesday. An
elongated upper level trough in the vicinity of the state, is seen
in water vapor imagery. This will cause the airmass to be
slightly less stable. The increase in showers will mainly occur
over windward and mauka areas, but the trade winds are
sufficiently strong enough to blow some showers over select
leeward areas at times. We can also expect daytime heating to
cause cloud buildups and a few showers to fall over the leeward
Big Island slopes this afternoon and evening.

The upper trough is forecast to weaken and lift out to the north
and west later Wednesday through Friday. This will stabilize the
airmass with showers becoming less prevalent. Meanwhile, the
surface high far to our north will strengthen a bit causing a
slight uptick in trade winds speeds.

As we head into the weekend, the high to our north will slowly
weaken with a slight downward trend in trade wind speeds. The
above mentioned trough will sag back southward, closer to the
state. This may cause for a slight uptick shower activity, mainly
for windward and mauka areas. Daytime heating will continue to
allow for clouds and showers to form over the leeward Big Island
slopes each afternoon and evening.


High pressure north of the island chain continues to bring
moderate to breezy trades to the state. An area of increased
moisture east of the state will be brought in by the trade flow,
bringing an uptick in clouds and showers primarily along windward
coasts and slopes this afternoon. This may result in occasional
MVFR conditions, but VFR conditions are expected to dominate.

AIRMET Tango remains in effect for south through west areas of
all islands below 7000 feet for tempo moderate turbulence. Will
continue to monitor conditions for possible AIRMET Sierra for
mountain obscuration, but is not expected at this time.


A weak trough of low pressure northwest of Kauai, will continue
to move west and away from the state over the next few days. High
pressure north of the area will strengthen on Wednesday and will
lead to fresh to strong trades through Friday. The trades could
ease slightly over the weekend, as high pressure to the north
weakens. A Small Craft Advisory (SCA) remains in effect for the
typically windy waters around the Big Island and Maui. The SCA
will likely need to be expanded to include additional zones around
mid week.

The current south swell will continue to slowly subside through mid-
week, with only small background south and southwest swells expected
for the end of the work week and over the upcoming weekend.
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 small. East shore surf will get a
boost Thursday into the weekend as the upstream fetch of trade
winds increases. Surf is expected to stay just below advisory
levels along east facing shores Thursday and Friday.


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

Small Craft Advisory from 6 PM this evening to 6 PM HST
Wednesday for Oahu Leeward Waters-Kaiwi Channel-Maui County
Windward 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
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