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Hawaiian Islands Synoptic Discussion and Guidance

660
FXHW60 PHFO 231936
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
936 AM HST Wed Oct 23 2019

.SYNOPSIS...
Trades will ease tonight through Friday as a front approaches
from the northwest, then strengthen Saturday through early next
week as high pressure rebuilds north of the island chain. Typical
trade wind weather will prevail, with showers favoring windward
and mauka areas.

&&

.DISCUSSION...
A 1032 mb high far northeast of the main Hawaiian Islands is
driving moderate to locally breezy trade winds across local waters
this morning. Satellite imagery shows mostly cloudy skies across
windward sections of Maui County and the Big Island, with partly
cloudy skies noted elsewhere. Radar shows isolated to scattered
showers moving across windward areas, with shower coverage the
greatest across windward sections of Maui County and the Big
Island.

Models show locally breezy trade winds will remain in place
today. A weakening cold front will approach from the northwest
tonight and Thursday, then stall out a few hundred miles north of
Kauai through the weekend. A second cold front will approach from
the northwest over the weekend and stall out in roughly the same
position, a few hundred miles north of Kauai, early next week.
Trades will decrease into the light to moderate range late tonight
through Friday night, with localized land and sea breezes
possible in the more sheltered locations. Trades will then
strengthen Saturday through early next week as high pressure
rebuilds to our north. Trade wind weather should prevail, even as
wind speeds fluctuate, with showers favoring windward and mauka
areas. However, leeward showers may increase Thursday and Friday
as trades ease just enough for leeward sea breeze development.
Overall however, rainfall amounts should remain light through
early next week.

&&

.AVIATION...
An approaching cold front north of the island chain will
gradually knock our moderate to locally breezy trade wind speeds
down a notch or two into Thursday. Clouds and showers will favor
windward and mauka slopes and coasts. Brief periods with MVFR
ceilings and visibilities will be possible in and around passing
showers. Elsewhere, VFR conditions will prevail.

AIRMET Tango remains in effect for areas south and west of the
mountains of all islands for low-level turbulence below 8,000ft,
but will likely be dropped later today as wind speeds decrease.

&&

.MARINE...
A ridge of high pressure several hundred miles N of Kauai continues
to support locally strong trade winds, and a Small Craft Advisory
(SCA) remains posted through today for marine zones around Maui
and the Big Island. An approaching front will force the ridge S
and weaken it over the next day or two, leading to weakening
winds that will veer slightly toward the SE. Like last weekend,
this effect will be most pronounced on the W end of the island
chain, but light E to SE winds will prevail over most areas from
late tonight into Saturday.

The front will stall and dissipate well N of the area Thursday
and Friday, but the ridge will remain suppressed southward near
the islands into Saturday as a second front approaches. High
pressure building NW of this second front will start to tighten
the local pressure gradient by late Saturday, leading to an
increase in trade wind speeds heading into next week. As this high
passes N of the area through early next week, it is expected to
support light to moderate trade winds.

A series of small to moderate northwest swells will fill in along
north and west facing shores over the next several days. A mid-period
NW swell arriving Thursday will veer to the N on Friday while
peaking below advisory levels, then diminish Saturday. A powerful
low (with hurricane-force winds) will develop in the NW Pacific
over the next 24 hours, generating a long- period NW swell that
will arrive Saturday night and persist through Tuesday. Peak surf
heights will almost certainly warrant a HSA for several days.
Elsewhere, short-period wind waves will gradually diminish along
E facing shores as trade winds ease the next couple of days. Small
to tiny background surf is expected along south facing shores over
the next several days.

&&

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

&&

$$

DISCUSSION...Powell
AVIATION...Dye
MARINE...Kino

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