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Hawaiian Islands Synoptic Discussion and Guidance

921
FXHW60 PHFO 100645
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
845 PM HST Sun Aug 9 2020

.SYNOPSIS...
A high pressure ridge north of the state will keep moderate to
breezy trade winds in the forecast for one more day. Wind speeds
will gradually decrease through the first half of the week as the
ridge weakens. Expect passing trade wind showers through the week
favoring windward and mountain areas, especially in the overnight
and early morning hours.

&&

.DISCUSSION...
The satellite picture this evening shows a narrow, southwest to
northeast oriented, upper level trough north of the islands with
several weak lows lingering along the trough axis (TUTT). A few
bands of clouds are east of the islands drifting into the windward
and mountain areas later tonight. The tropical convergence zone
south of the state is showing increasing activity trends.

The high pressure system north of the island chain will slowly
weaken over the next two days, decreasing the wind speeds over the
islands each day. Our moderate to breezy trade winds will
gradually decrease into the light to moderate range by Wednesday
and remain on the lighter side into the upcoming weekend.

Expect scattered showers favoring windward and mountain areas
during the day becoming numerous from the overnight to early
morning time periods. More isolated activity remains in the
forecast over leeward areas. These brief passing showers affecting
all islands will likely continue through the upcoming weekend.

&&

.AVIATION...
Fresh to locally strong trades will support scattered showers with
periods of low ceilings particularly over windward coasts and
slopes. Mountain obscuration lingers over windward Maui and Big
Island due to the remnants of a band of showery low clouds, so
AIRMET Sierra remains in effect above 2000 for those areas.
Slightly drier trades are forecast to work into the area later
tonight.

AIRMET TANGO remains in effect below 7000 feet over and south
thru west of mountains for tempo moderate turbulence.

&&

.MARINE...
Fresh to strong trade winds will continue into Monday, then trend
down into the moderate to fresh range Tuesday through the rest of
the week as high pressure weakens to the north. Seas will remain
at or near the 10 ft advisory level into Monday across the
Alenuihaha Channel and over the waters south of the Big Island,
then subside Tuesday through midweek.

Surf along east facing shores will remain rough through Monday due
to the gusty trades. Although the surf will lower by midweek as
the winds relax locally, an upward trend is possible through the
second half of the week. Guidance depicts a decent sized area of
strong winds focused at the islands within the 040-050 degree band
off the California coast through Tuesday, which should correspond
to a medium period groundswell out of the northeast arriving
around Thursday. Surf along north facing shores exposed to this
direction will also rise through this time.

Surf along south facing shores will remain small through the
week with mainly a mix of small, short-period southeast and
background south-southwest energy moving through.

&&

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

Small Craft Advisory until 6 AM HST Monday for Oahu Leeward
Waters-Kaiwi Channel-Maui County Windward Waters.

&&

$$

DISCUSSION...Bohlin
AVIATION...Powell
MARINE...Gibbs

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

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