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RH21 %
WindNE 20 mph
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Hawaiian Islands Synoptic Discussion and Guidance

233
FXHW60 PHFO 251947
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
947 AM HST Sun Aug 25 2019

.SYNOPSIS...
A trade wind weather pattern will continue through Monday, thanks
to high pressure far north of the area. Trade winds will become
lighter Tuesday through Friday as an area of low pressure develops
far north of the area. Local land and sea breezes are expected to
develop across some areas under this lighter trade wind regime. A
new high is expected to build in far north northwest of the area
next weekend with an uptick in trade winds expected. Clouds and
passing showers will tend to favor windward and mauka areas with
afternoon clouds and showers possible over the leeward Big Island
slopes through the forecast period.

&&

.DISCUSSION...
Surface high pressure is centered far north of the state. This
places the islands in a moderate to locally breezy trade wind
environment. Aloft, there is a mid level ridge in place over the
area. This is providing for a rather stable airmass to be in place
across the state. Thus any showers that do form will tend to be
on the lighter side due to inhibited cloud growth. The surface
high will continue to keep moderate to breezy trade winds in place
through Monday while the upper ridge will keep inversion heights
low with only light windward and mauka showers expected. Afternoon
and evening clouds and showers are also expected over the leeward
Big Island slopes.

During the Tuesday through Friday time frame, the high is
forecast to weaken and move off to the northeast while an area of
low pressure develops far to our north. This will cause our trade
winds to weaken to the light to locally moderate range. Localized
land and sea breezes may develop under this lighter trade wind
regime. Meanwhile, the state is forecast to lie between a mid
level ridge northwest of the state and a mid level trough just
east of the state. Thus instability will be limited under this
scenario. Shower activity will be highly dependent on incoming
moisture availability and primarily focused over windward and
mauka area. Daytime heating may allow for some afternoon shower
development over interior areas as well as over the leeward Big
Island slopes.

As we head into next weekend, a new high is forecast to begin
building in far to our north northwest while the area of low
pressure moves off to the northeast. This should allow for an
uptick in trade wind speeds across the area. Clouds and passing
showers will tend to favor windward and mauka areas under this
weather regime.

&&

.AVIATION...
High pressure north/northeast of Hawaii will continue to bring
breezy trade winds to the state. So not much change from Saturday's
weather except winds will tend to be a little stronger and there
should be a few more showers in windward/mauka areas this
afternoon and through tonight for Maui County and the Big Island.
Will issue an AIRMET accordingly if necessary. The winds may also
be strong enough on these islands to blow a few showers into
leeward sections. AIRMET Tango continues for mechanical turbulence
downwind of all the mountains below 8,000 feet. This AIRMET will
likely continue through today and into tonight with little change
in winds expected except the winds may be a little weaker Monday.

VFR conditions are expected to prevail most of today with passing
MVFR conditions in passing clouds and showers primarily over the
windward slopes. There may be a more steady MVFR conditions for
Maui County and the Big Island late today and overnight tonight as
more moisture works into the windward areas of these islands.

&&

.MARINE...
Fresh to strong easterly trade winds will continue today as high
pressure remains far north of the state. The Small Craft Advisory
(SCA) has been expanded from the typically windy waters around the
Big Island and Maui to briefly cover the Maui County windward and
Kaiwi Channel waters today. Trades will gradually decrease through
the first half of the week as the high weakens and drifts northeast.
Advisory level winds will likely scale back to the usual windy areas
Monday afternoon, and then drop completely by Tuesday.

South shore surf will remain around the summer background level for
the next few days as a southwest swell out of the Tasman Sea arrives
Tuesday, peaks Wednesday and Thursday, then declines into next weekend.
Though Hawaii is largely blocked by swells from this direction,some
slightly higher, but inconsistent, sets are possible during the peak.

Expect a slight and brief increase in east shore surf today as trades
strengthen, followed by a gradual decline through the rest of the
week. North shore surf will remain small through the week.

&&

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

Small Craft Advisory until 6 PM HST this evening for Kaiwi
Channel-Maui County Windward Waters.

&&

$$

DISCUSSION...Burke
AVIATION...Chevalier
MARINE...TS

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