Area Forecast Discussion
Issued by NWS Honolulu, HI

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308
FXHW60 PHFO 221332
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
332 AM HST Tue Oct 22 2019

.SYNOPSIS...
High pressure northeast of the state will keep moderate to locally
breezy trade winds in place through Wednesday. The trades will
ease Thursday through Saturday as a series of fronts approach from
the northwest. The trades are then expected to strengthen Sunday
through early next week. Fairly typical trade wind weather will
prevail, with showers favoring windward and mauka areas and a
stray shower reaching leeward locales from time to time.

&&

.DISCUSSION...
Currently at the surface, a 1031 mb high is centered around 1775
miles northeast of Honolulu, while a cold front is located around
1275 miles west-northwest of Kauai. The resulting gradient is
producing moderate to locally breezy trade winds across the island
chain early this morning. Infrared satellite imagery shows partly
cloudy skies in windward areas of the smaller islands, with
mostly cloudy conditions in place over windward Big Island. Clear
to partly cloudy conditions prevail in most leeward locales. Radar
imagery shows isolated to scattered showers moving into windward
areas, with shower coverage the greatest across windward Big
Island. Mainly rain free conditions are in place in leeward
locales. Main short term concerns over the next several days
revolve around trade wind trends and rainfall chances.

High pressure northeast of the state will keep moderate to
locally breezy trade winds in place through Wednesday. A
weakening cold front will approach from the northwest Wednesday
night and Thursday, then stall out a few hundred miles north of
Kauai through the weekend. A secondary 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.
These fronts should ease the trades into the light to moderate
range Thursday through Saturday, with localized land and sea
breezes possible in the more sheltered locations. Moderate trade
winds will try to make a return Sunday through early next week as
the gradient across the island chain tightens up due to high
pressure strengthening to the north of the state.

As for forecast details, fairly typical trade wind weather should
prevail during the next 7 days, with showers favoring windward
and mauka areas, particularly at night through mid morning each
day. A stray shower will also reach leeward areas from time to
time. There could be a slight increase in leeward shower activity
Thursday through Saturday as the trade winds ease, allowing for
some sea breeze driven shower development as well. Overall,
rainfall amounts are expected to remain on the light side through
early next week.

&&

.AVIATION...
Passing, isolated areas of MVFR conditions on the windward side
of the islands are expected through this forecast period. Will
monitor and issue an AIRMET for mountain obscuration if necessary.
Otherwise, the rest of the state will see VFR conditions.

AIRMET Tango is in effect now for areas south and west of the
mountains for low-level turbulence below 8,000 ft. Will probably
continue this AIRMET through today. May be able to drop this
AIRMET later tonight or Wednesday as winds are expected to
weaken.

&&

.MARINE...
High pressure centered far northeast of the islands will maintain
moderate to strong trades through Wednesday. The evening ASCAT pass
revealed small craft advisory level (SCA) winds extending beyond
its usual near-shore waters of Maui County and waters south of the
Big Island. The SCA now includes the windward waters of Maui
County and leeward waters of Oahu. These additional waters are
good until late tonight. With this weakening trend, the last of
the SCA, which include the typically windy areas of Maui County
and waters south of the Big Island, is set to expire late
Wednesday afternoon.

The weakening of the trades is being caused by a front settling
some 450 miles north of Kauai by Thursday. The front may linger
near the northern extreme of our offshore waters into the upcoming
weekend. Additionally, a weak area of surface low pressure is
expected to form some 850 miles northwest of Kauai as well, which
may help in maintaining moderate trades across the island waters
over the weekend.

Small surf will remain along all shores today. A series of
northwest swells are then expected over the coming days with each
bump being a little bit larger. A small bump first rolls in on
Wednesday followed by a moderate northwest swell on Friday. Then,
on Saturday night, a large northwest swell arrives, bringing
advisory level surf to the north and west facing shores between
Sunday and Tuesday. This swell will peak Monday before trending
down slowly.

Locally strong trade winds will maintain mainly moderate level surf
along east facing shores through Wednesday, followed by slightly
smaller surf during the second half of the week as the trades become
lighter. A small background swell will maintain small surf for the
south facing shores through the rest of the period.

&&

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

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

&&

$$

DISCUSSION...Jelsema
AVIATION...Chevalier
MARINE...H Lau



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