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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 161337

Area Forecast Discussion
National Weather Service Honolulu HI
337 AM HST Sun Jun 16 2019

A fairly dry trade wind weather pattern will continue through most
of next week. Clouds and isolated to scattered showers will
remain in the forecast over windward and mountain areas favoring
the overnight and early morning hours. Brief periods of isolated
showers are forecast over leeward areas.


Another extended period of fairly dry trade wind weather remains
in the forecast through next week. Subtle changes in the strength
and position of the high pressure ridge north of the islands will
result in slight adjustments to trade winds and windward shower
coverage over the next seven days. Expect moderate to breezy trade
winds to continue today with isolated to scattered shower
activity over windward and mountain areas in the morning hours.

In the big picture, the subtropical ridge north of the islands
continues to produce moderate to breezy trade winds today. A
long wave trough remains anchored over the Central Pacific basin.
Subtle changes in the intensity of this long wave trough will
impact the strength of the ridge north of the islands, modifying
the trade wind direction and speed for the upcoming work week.

For today, A strong upper level ridge will keep the best chances
for showers over windward and mountain areas this morning, with
trade wind subsidence inversion heights around 5000 to 7000 feet.
This ridge weakens later tonight as an upper level trough deepens
over the state.

On Monday and Tuesday, the long wave trough deepens over the
Central Pacific weakening the subtropical ridge north of the
islands. These changing large scale pressure patterns will place
the Hawaiian Islands along the southwestern edge of the surface
ridge axis, causing low level wind directions to veer towards the
east to southeast direction. At the same time step, an upper
trough deepens over the state. Wind speeds will weaken slightly
on Monday and Tuesday with modified land and sea breezes expanding
along sheltered leeward slopes. Dynamic lift associated with the
upper trough will decrease atmospheric stability, allowing for
more scattered windward and mauka showers and isolated leeward
showers favoring the overnight and early morning hours. Trade
wind subsidence inversion heights will rise into the 7000 to 9000
foot range by Monday night.

Wednesday through Friday, the surface ridge north of the islands
builds slightly and trade winds back towards a more easterly
direction. The subtropical jet stream will develop over the
islands spreading high cirrus clouds across the state. A building
upper level ridge will bring another round of more stable
conditions with subsidence inversion heights falling back down
into the 5000 to 7000 foot range on Wednesday and Thursday. A weak
upper trough will bring a return to more scattered windward and
mauka showers from Friday night into Saturday morning.


Surface high pressure will remain to the northeast of Hawaii,
providing moderate to locally strong trade winds to the area today.
Passing low clouds will affect windward and mountain areas of the
islands at times, bringing some showers. Mainly VFR conditions
will prevail, though windward and mountain areas may see brief
MVFR ceiling and VIS.

No AIRMETS are expected today, though the potential for AIRMET
Tango for low-level turbulence continues due to the rather robust
trade winds.


High pressure far northeast of the state will maintain fresh to
locally strong trades through the middle of the week. Winds may
veer east-southeasterly Monday into Tuesday as a weak trough
develops far west of the state. A Small Craft Advisory (SCA) is in
effect for the typically windy waters around the Big Island and
Maui through early Monday morning. This will likely need to be
extended at least into Tuesday.

Somewhat elevated surf is expected along south facing shores
through today, though the High Surf Advisory has been cancelled.
We should see several reinforcing south-southwest swells for the
first half of the week, with surf heights around the summer
average through at least midweek.

A reinforcing northwest swell will continue to produce surf in
the small to moderate range along north facing shores through
today. Additional pulses of tiny northwest swell are expected
through the week. Also, surf along east facing shores will begin
to rise early this week as trade winds become more established.


Small Craft Advisory until 6 AM HST Monday 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
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