Area Forecast Discussion
Issued by NWS Honolulu, HI

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691
FXHW60 PHFO 232026 CCA
AFDHFO

Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
1026 AM HST Wed May 23 2018

.SYNOPSIS...
Trade winds will continue through the holiday weekend and into next
week, periodically delivering clouds and showers to windward
portions of the islands. Winds will be locally strong into Saturday
before easing somewhat Sunday and Monday. Showers may be especially
active on Saturday as an area of increased moisture moves through,
and then again on Tuesday.

&&

.DISCUSSION...
Relatively strong high pressure passing well N of the islands is
supporting locally strong trade winds, and will continue to do so
into the weekend as it moves steadily E. The island atmosphere is
stable, with a strong subsidence inversion near 8000 feet keeping a
lid on the low clouds arriving in the trade wind flow. This will
change little into Friday, with randomly distributed showery low
clouds bringing passing showers that primarily favor windward
areas. In the short term, low clouds are in greater concentration
upstream of the islands from Maui to Kauai, with very little in
the way of low clouds immediately upstream of the Big Island.
Despite that, lower slopes of the Big Island are covered in broken
to overcast low clouds.

A mid-level ridge will remain in place over the islands into early
next week, keeping the island atmosphere stable, and limiting shower
intensity. However, the mixed-layer is sufficiently deep to support
showers, which will primarily fall over windward slopes and coasts.
Fragmented remnants of a front N of the area today (near 27N) are
expected to become embedded in the trade wind flow, bringing an
increase in low-level moisture/windward showers Friday night and
Saturday.

The mid-level ridge is forecast to weaken on Sunday/Monday as a low
aloft develops overhead. This could bring an increase in trade
showers late Monday and Tuesday, and may induce a surface trough
near or W of the islands by the middle of next week. While too soon
to have much confidence, if this were to occur, winds near the
active lava flows and erupting volcano on the Big Island could
become problematic.

&&

.AVIATION...
VFR conditions prevail at all TAF sites and these conditions are
expected to prevail through the day. There may be some brief MVFR
conditions at windward terminals and over windward slopes in low
clouds and -shra.

AIRMET TANGO is currently posted for low level turbulence over and
immediately south and west of mountains below 8000 feet on all
islands.

Periodic explosive eruptions at Kilauea/Halemaumau crater continue
to produce periods of volcanic ash, with the plume of emissions
predominately rising to the inversion level and extending to the
southwest over Kau district on the Big Island. MVFR VIS can be
expected in this area. Volcanic ash SIGMET TANGO series remains in
place at this time.

&&

.MARINE...
High pressure passing by to the north of the state will keep a
breezy trade wind flow in place across the coastal waters through
Saturday. The trades are expected to trend down Sunday through early
next week as an approaching front shifts the high northeastward away
from the island chain. A Small Craft Advisory (SCA) is in effect for
most marine zones through tonight, then most waters east of the
Kauai Channel through Thursday night. SCA conditions will likely
continue into the weekend for the typically windy waters around Maui
and the Big Island, so expect that advisory to be extended later
this week.

No significant swells are expected, with surf remaining below
advisory levels into next week. A small, long-period south-southwest
swell will slowly build today, then continue into the weekend. A
small north-northwest swell will peak today then slowly diminish
through Thursday. Another small northwest swell may give surf a
slight bump along north facing shores over the weekend. Breezy trade
winds will deliver choppy short-period waves to east facing shores
into the weekend.

&&

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

Small Craft Advisory until 6 AM HST Friday for Oahu Windward Waters-
Oahu Leeward Waters-Kaiwi Channel-Maui County Windward Waters-Maui
County Leeward Waters.

Small Craft Advisory until 6 AM HST Thursday for Kauai Northwest
Waters-Kauai Channel.

&&

$$

Discussion...Birchard
Marine...TS
Aviation...Burke



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