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Hawaiian Islands Synoptic Discussion and Guidance

559
FXHW60 PHFO 191934
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
934 AM HST Fri Apr 19 2019

.SYNOPSIS...
Moderate to locally breezy trade winds will prevail through much
of the week as surface high pressure holds north of the state.
Rather stable conditions will remain in place, leading to a
typical pattern of mainly windward and mauka showers.

&&

.DISCUSSION...
A stable, moderate to locally breezy trade wind flow persists. The
trades are being generated by strong high pressure located far
northeast of the state and its associated surface ridge sitting
about 300 miles north of Kauai. A mid level ridge building in from
the west is producing stable conditions and a fairly strong strong
inversion between 4,500 ft to nearly 8,000 ft according to
overnight soundings and recent aircraft data. Moisture in the
trade wind flow is generally near April normal, which has resulted
in modest rainfall (around 1/4 of an inch or less) across windward
terrain this morning. Leeward areas have remained mostly dry.

A typical trade wind weather pattern is expected through much the
upcoming week. We will likely see an uptick in trade winds during
the weekend as the ridge to the north briefly strengthens, with
little change in the trades through Thursday as surface high
pressure prevails to the north of the state. Stable conditions
will dominate through much of the week as the mid level ridge will
remain parked overhead, and generally, precipitable water will be
near normal, suggesting that showers will be modest and confined
to windward slopes. As random pockets of low level moisture move
through on the trade wind flow, expect brief and localized
increases in showers. Aside from afternoon showers on the Kona
slopes of the Big Island, leeward areas will be mostly dry.

&&

.AVIATION...
A high pressure ridge north of the state will keep the islands in
a moderate to breezy trade wind weather pattern through the
weekend. Near surface wind speeds are strong enough to support
moderate low level turbulence over and south through west of
mountain ranges of all islands. Scattered shower activity will
favor windward and mountain sections with brief periods of MVFR
conditions mainly during the overnight hours.

AIRMET Tango remains in effect for tempo moderate turbulence below
080. This AIRMET will likely remain in effect through the
weekend.

&&

.MARINE...
Fresh to strong trades will continue into early next week as a
ridge remains north of the islands. The Small Craft Advisory (SCA)
remains posted for the typical windier areas near Maui County and
the Big Island through Sunday afternoon. Models indicate an uptick
in the winds late tonight and tomorrow as the ridge strengthens,
which will likely warrant adding the windward Maui and Big Island
zones to the SCA this afternoon. It also remains possible that the
SCA for the typical windy zones will be extended into next week.

The current north-northwest swell is expected to peak today below
advisory levels, then slowly decline through the weekend. A small,
west-northwest swell is possible early next week, but again remain
below advisory surf levels.

Background south-southwest swells will keep surf small along south
facing shores through the weekend. An upward trend is expected
early next week though, due to recent activity southeast of New
Zealand, and should correlate to above average south shore surf
continuing into midweek.

Surf along east facing shores could see a bump over the weekend
with an uptick in the trades. See the latest Oahu Surf Discussion
(SRDHFO) for additional details on surf and swell.

&&

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

&&

$$

DISCUSSION...Wroe
AVIATION...Bedal
MARINE...TS

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



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