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Hawaiian Islands Synoptic Discussion and Guidance

471
FXHW60 PHFO 230140
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
340 PM HST Tue Oct 22 2019

.SYNOPSIS...
A ridge to the north will maintain locally breezy easterly trade
winds over the area through tomorrow. The trades will focus winds
over mainly windward areas. Winds will weaken from tomorrow
evening through the weekend as a couple of fronts approach from
the northwest. Moisture from a tropical disturbance may increase
rain on the Big Island Friday night.

&&

.DISCUSSION...
Satellite loops and surface observations show partly cloudy skies
over the islands. Breezy easterly trade winds are blowing across
the area. Radars show only isolated light showers moving along in
the trade-wind flow.

The 2 PM surface analysis shows a strong 1031 mb surface high far
northeast of the state near 38N 137W. A ridge extends southwest
from the high to about 300 miles northwest of Kauai. A front lies
about 825 miles northwest of the islands and a weak trough is
about 800 miles to the south. The pressure gradient between the
ridge north of the islands and the trough to the south will
maintain breezy trade winds over the islands through tomorrow.

The ridge northwest of the area is forecast to erode over the
second half of the week as a series of fronts approach from the
northwest. The fronts will stall well northwest of the islands,
but trade winds will weaken as the ridge erodes. The trade winds
will continue to carry some clouds and showers over windward
areas, but rainfall should generally be light through Friday
morning. An area of moisture associated with a tropical
disturbance southeast of the islands could spread north far enough
to bring an increase in showers to the Big Island Friday night,
but it remains uncertain how far north the moisture will spread.

&&

.AVIATION...
Moderate to locally breezy trades will continue into tomorrow
before weakening. While shower activity has been light through
most of the day, coverage is expected to increase into the
overnight hours. These showers will favor windward and mauka
locales, particularly on the Big Island as an area of increased
moisture moves in from the east. This may result in brief periods
of MVFR conditions. Elsewhere, VFR 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. May
be able to drop this AIRMET later tonight into Wednesday as winds
are expected to weaken.

&&

.MARINE...
A high pressure centered far northeast of the islands will
maintain moderate to strong trades through Wednesday over the
coastal waters. A Small Craft Advisory (SCA) is posted through
tonight for the typical windy waters around Maui County and the
Big Island plus windward Maui waters and leeward Oahu waters. The
SCA will continue through tomorrow for the typically windy waters
around the Big Island and Maui.

Trade winds will weaken Thursday and Friday as a front approaches
from the northwest. Winds will shift slightly east southeast
during this time and weaken to gentle to moderate speeds. A second
front will approach over the weekend and maintain the lighter
than normal winds into early next week.

A series of northwest swells is expected over the coming days
with each bump being a little bit larger. A small bump first rolls
in late tonight and Wednesday morning followed by a moderate
north swell on Friday. A large northwest swell will build on
Sunday, bringing advisory level surf to the north and west facing
shores between Sunday and Tuesday. This swell will peak Monday
before trending down slowly.

Moderate, choppy surf will continue along east facing shores
through Thursday, then subside as the winds weaken. Surf will
remain small along south facing shores.

&&

.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...Donaldson
AVIATION...Dye
MARINE...Foster

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



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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
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