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Hawaiian Islands Synoptic Discussion and Guidance

132
FXHW60 PHFO 220637
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
837 PM HST Mon Oct 21 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 through the weekend, 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 1800
miles northeast of Honolulu, while a cold front is located around
1550 miles west-northwest of Kauai. The resulting gradient is
producing moderate to locally breezy trade winds across the
island chain this evening. Infrared satellite imagery shows partly
to mostly cloudy skies in windward areas, with primarily partly
cloudy conditions in leeward locales. Radar imagery shows isolated
to scattered windward showers, with mainly rain free conditions
in leeward areas, with the exception of leeward Big Island where a
few lingering daytime showers remain. 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. This 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 a bit.

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.

&&

.AVIATION...
We are only expecting to have passing, isolated areas of MVFR
conditions on the windward side of the islands. 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 Tuesday. May be able to drop this
AIRMET Tuesday night into Wednesday as winds are expected to
weaken.

&&

.MARINE...
High pressure centered far northeast of the area will maintain
moderate to locally strong trades through Wednesday before
weakening. A Small Craft Advisory (SCA) is in effect for the
commonly windy near-shore waters around Maui County and the Big
Island through early Wednesday morning. The weakening of the
trades is being caused by a front settling some 450 miles north
of Kauai by Thursday. The front will linger near the northern
extreme of our offshore waters through the second half of the
week and may touch the northern extreme of our offshore waters
before edging slightly north over the weekend. A weak area of
surface low pressure is expected to persist some 850 miles
northwest of Kauai, thus maintaining moderate trades across the
island waters over the upcoming weekend.

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

The locally strong trade winds will maintain mainly moderate level
surf along east facing shores through Wednesday, followed by
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 week.

&&

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

&&

$$

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

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