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RH24 %
WindNE 24 mph
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Hawaiian Islands Synoptic Discussion and Guidance

226
FXHW60 PHFO 260143
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
343 PM 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. Long range model
guidance is beginning to indicate that we may see an increase in
moisture moving in from the east and southeast. Confidence on
details that far out are rather low. Clouds and passing showers
will tend to favor windward and mauka areas under this weather
regime though it may become a bit more active if this were to
occur.

&&

.AVIATION...
High pressure north/northeast of Hawaii will continue to bring
breezy to windy trade winds to the state. We should have an
increased chance for windward showers later tonight and into
Monday for Maui County and the Big island. There may be lower CIGs
and VIS as a result. 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 during evening hours.
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. The trend
for weaker winds should continue into Monday night and Tuesday
with a weakening pressure gradient.

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 more steady MVFR conditions for
Maui County and the Big Island late tonight into Monday as more
moisture works into the windward areas of these islands.

&&

.MARINE...
Fresh to strong easterly trade winds will continue tonight as high
pressure remains far north of the state. The Small Craft Advisory
(SCA) has been extended through tonight for the Maui County windward
and Kaiwi Channel waters and through Monday afternoon for the typically
windy waters around the Big Island and Maui. Trades will gradually
decrease through the first half of the week as the high weakens and
drifts northeast, with advisory level winds scaling back to only 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 couple of 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.

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 PM HST Monday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

Small Craft Advisory until 6 AM HST Monday 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