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Hawaiian Islands Synoptic Discussion and Guidance

815
FXHW60 PHFO 171944
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
944 AM HST Thu Oct 17 2019

.SYNOPSIS...
Breezy trade winds and passing windward showers are expected
into next week. Humidity and rainfall may increase a notch over
the weekend as tropical moisture moves over the island chain.

&&

.DISCUSSION...
No changes to the forecast at this time, but anticipate fine
tuning some of the PoPs and associated fields with the afternoon
package.

The overnight surface analysis showed a surface trough to the
northwest of Kauai, which is expected to continue to move to the
west and weaken. The mid to upper level low associated with this
system is further to the west and continues to move away from the
islands, allowing a more stable airmass to move overhead. High
pressure far north of the islands is bringing trade winds back to
the area, and these should continue into next week. Good model
agreement with the high slowly moving to the east through the
weekend.

A front approaching from the northwest this weekend will help to
bring in more tropical moisture from the south. At the same time,
we could see the winds shift to a bit more of a southeasterly
direction at the end of the weekend. The front is not expected to
reach the islands.

Models agree with the high lifting northward next week, which
could be weakening our trade winds a bit. Moisture riding in on
the trades could mean a wetter trade wind pattern.

&&

.AVIATION...
As an upper-level low moves west away from the state today, some
lingering instability will continue shower activity around leeward
Kauai. Otherwise, moderate easterly trades will push much of the
shower activity against the windward coasts and slopes, though
isolated -SHRA may periodically push over onto leeward sides. Brief
MVFR conditions are possible in these areas, but overall, VFR will
prevail through tonight.

&&

.MARINE...
A strong high north of the area will maintain locally strong
easterly trade winds over the coastal waters through at least
Saturday. A Small Craft Advisory (SCA) remains in effect for
Maalaea Bay, the Pailolo and Alenuihaha Channels and waters south
of the Big Island. The SCA will likely need to be extended into
the weekend. Winds are forecast to weaken and veer to the east-
southeast starting Saturday night as the high moves farther east
and a front approaches from the northwest.

Near-shore buoys continue to show an increase in energy as the
new west-northwest swell and north swell fills in this morning.
These swells are expected to peak well below advisory levels later
today into tonight and gradually decline through the weekend. A
small reinforcing north-northwest swell is expected on Saturday.

Background swells will continue to provide small surf along south
facing shores over the next few days. Last week, a storm force low
far southeast of New Zealand, tracked east with seas growing to 30
to 40 feet near 60S 150W. Although most of the swell will pass
east of the state, we should see an increase in long-period surf along
south facing shores starting Friday night due to angular
spreading. This swell will likely peak Saturday night and
gradually subside through early next week.

&&

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

&&

$$


DISCUSSION...M Ballard
AVIATION...TS
MARINE...Kino

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