Volcanic Ashfall in Hawaii, June 1 to 4, 2018

Area Forecast Discussion
National Weather Service Honolulu HI
816 PM HST Thu May 31 2018

.SYNOPSIS...
Moderate trade winds will persist into Saturday then become breezy
to locally windy conditions from Sunday through at least the
first half of next week as high pressure strengthens north of the
state. Showers riding in on the trades will favor the windward and
mauka areas, with a few showers briefly spreading leeward through
Friday. An upper level low northwest of the islands will bring
continued high cirrus clouds across the state with enhanced
showers over the western half of the state this weekend. A return
to more typical trade wind weather is anticipated for the first
half of next week with clouds and showers favoring windward and
mauka sections of each island.

&&

.DISCUSSION...
A 1028 MB surface high pressure system roughly 1000 miles north
of the state will keep moderate trade winds in the forecast
through Saturday. A stronger 1033 mb surface high center moves
into the region on Sunday with trade winds increasing to breezy
with locally windy conditions from Sunday through Wednesday.

An upper level low northwest of the islands with a subtropical jet
stream will continue to push high level cirrus clouds over the
state through the weekend. This upper low will drift east towards
the islands on Friday, weakening to a open trough as the weather
pattern north of the islands shifts. A shot of cold air will move
in from the north on Saturday intensifying this low center,
destabilizing the upper levels by lifting the trade wind inversion
height, and enhancing shower activity across the western half of
the state through Sunday. The upper level low center will then
drift southwest away from the islands on Monday as a mid level
ridge builds back in helping to stabilize the upper levels of the
atmosphere. Expect a return to more typical trade wind weather for
the first half of next week with clouds and showers favoring
windward and mauka areas.

A Special Weather Statement continues to highlight the potential
for volcanic emissions and ashfall from Halemaumau Crater on the
Big Island. It also highlights the potential for Pele's hair and
other volcanic emissions that are being transported downwind from
high fountaining fissures in the Puna District.

&&

.AVIATION...
Trade wind flow will persist through 24 hours and beyond. Locally
brisk winds through channeled areas will diminish overnight--
only to redevelop tomorrow afternoon.

Clouds and showers will favor windward and mountain areas.
Isolated MVFR conditions in passing showers, otherwise VFR
conditions will prevail all areas.

Due to the minimal ash emission from the Kilauea/Halemaumau,
the Volcanic SIGMET has been canceled. Due to its unpredictable
nature, a Volcanic SIGMET can be reissued at any time. The
prevailing wind direction overnight will be from the NE along the
Windward Coast and light and variable along the Leeward Coast.
Therefore, smoke and vog from Kilauea and the Leilani Estates
fissures will continue to produce reduced visibilities downwind
across the Kau District and also the lower part of the Kona coast
through at least the early morning hours.

&&

.MARINE...
High pressure north of the state will keep moderate to locally
breezy trade winds in place through Saturday. A new strong high
will build north of the islands Sunday through the middle of next
week, increasing the trades to breezy and locally windy levels
once again. A Small Craft Advisory (SCA) remains in effect for
the typically windy waters around Maui County and the Big Island
through the weekend, and this will likely need to be extended
through the middle of next week. SCA conditions will likely
expand to include most marine zones on Sunday as the trade winds
increase, with these conditions continuing into early next week.

The current SW swell will continue to gradually trend downward
through Saturday. A larger S swell is forecast to arrive on Sunday
and peak at or near High Surf Advisory levels along south facing
shores early next week. Short period trade wind swell will
continue to bring average surf to east facing shores through
Saturday. East shore surf should increase again Sunday through the
middle of next week as breezy trades return. Surf will remain
small along north facing shores through early next week.

&&

.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...Bohlin
AVIATION...Bedal
MARINE...Jelsema