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Hawaiian Islands Synoptic Discussion and Guidance

381
FXHW60 PHFO 180228 CCA
AFDHFO

Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
428 PM HST Thu Oct 17 2019

Corrected format issue in the Marine section.

.SYNOPSIS...
Breezy trade winds and mostly 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 significant changes to the forecast this afternoon. Have
tweaked the PoPs and associated grids for the first 24 hours to
align better with the latest runs of the high resolution models.
These depict more rain on the western end of the state. The
general forecast philosophy remains the same with the afternoon
package.

The surface trough to the northwest of Kauai, 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.

&&

.MARINE...
A strong high north of the area will maintain locally strong
easterly trade winds over the coastal waters through at least
Saturday. The Small Craft Advisory (SCA) has been extended through
Saturday for Maalaea Bay, the Pailolo and Alenuihaha Channels and
waters south of the Big Island. 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.

Currently we have two swells in the water impacting north facing
shores. A small northwest swell that has most likely peaked, and a
building north swell. Buoy 51000 located about 250 miles NE of
Honolulu is currently peaking this afternoon. This should
translate to surf peaking tonight and steadily decreasing through
the day Friday along north facing shores. As these swells continue
to decline through the weekend, a small reinforcing north-
northwest swell is expected to fill in 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.

&&

.AVIATION...
As the upper-level low exits the area to the west, moderate
easterly trades will return and 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
Friday.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST Saturday 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