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RH12 %
WindNE 22 mph
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Hawaiian Islands Synoptic Discussion and Guidance

843
FXHW60 PHFO 200144
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
344 PM 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
nearly 350 miles north of Kauai. A mid level ridge overhead is
producing stable conditions and a fairly strong strong inversion
between 4,000 ft to 6,000 ft according to afternoon soundings and
recent aircraft data. Moisture in the trade wind flow is
generally near April normal, which has resulted in modest rainfall
(less than 1/4 of an inch) across windward terrain today. Leeward
areas have remained mostly dry.

A typical trade wind weather pattern is expected through much the
upcoming week. We will likely see a brief uptick in trade winds
during the weekend as the ridge to the north strengthens. Trades
will drop back into the moderate to locally breezy range on Monday
and persist through at least 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.

The GFS and ECMWF differ on the details, though both models show
an advancing front weakening the trade winds next Friday.

&&

.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 Saturday as the ridge strengthens, so windward Maui and Big
Island, as well as the Kaiwi Channel were added to the SCA for that
time period. It also remains likely 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.

Small Craft Advisory from 6 AM Saturday to 6 AM HST Sunday for
Kaiwi Channel-Maui County Windward Waters-Big Island Windward
Waters.

&&

$$

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

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