Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxhw60 phfo 240200 
afdhfo

Area forecast discussion
National Weather Service Honolulu HI
400 PM HST Wed may 23 2018

Synopsis...
trade winds will continue through the Holiday weekend and into next
week, periodically delivering clouds and showers that will focus
over windward areas. 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 may increase again on Tuesday.

&&

Discussion...
relatively strong high pressure passing well north of the islands
continues to support gusty trade winds, and will continue to do so
into the weekend as it moves steadily east. The island atmosphere is
stable, with a strong subsidence inversion near 7000 feet keeping a
lid on the low clouds arriving in the trade wind flow. This will
change little through Friday, with randomly distributed showery low
clouds bringing passing showers that will primarily favor windward
areas. In the short term, low clouds are in greater concentration
upstream of the islands from Maui to Kauai, and windward rain
chances will be pretty high through the night despite the stability.
While very little in the way of low clouds is noted immediately
upstream of windward Big Island, an area of showery low clouds about
150 to the east is expected to bring an increase in showers there later
tonight.

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, as seen today, the mixed-layer is sufficiently
deep to support showers, which will primarily fall over windward
slopes and coasts. Fragmented remnants of a front north of the area,
(currently east-northeast-west-southwest oriented along ~26n) are expected to become
embedded in the trade wind flow, bringing an increase in low-level
moisture/windward showers Friday night and Saturday.

The high will distance itself from the islands as it moves into the
NE Pacific late this weekend, the associated ridge north of the area will
be weakened by a passing front, and trade wind speeds will ease. The
mid-level ridge is forecast to weaken on Sunday/Monday as a low
aloft develops overhead by Tuesday. This could bring an increase in
trade showers late Monday and Tuesday, and may induce a surface
trough near or west 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.

In the meantime, a Special Weather Statement continues to highlight
the light ashfall that is occurring in portions of the big Island's
Kau district. Several bursts of ash from Halemaumau have been noted
in web cams and radar data today (extending as high as 5000-8000
feet), and all indications are that this activity will continue, at
least overnight.

&&

Aviation...
VFR conditions prevail at all taf sites and these conditions are
expected to prevail through the overnight hours. 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. These conditions are expected to continue tonight through
Thursday.

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 visible can be
expected in this area. Volcanic ash significant meteorological information 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 scales back to most waters
east of the Kauai Channel through Thursday night. Small Craft Advisory 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.

&&

$$

National Weather Service Glossary of Abbreviations