Wildfire in Hawaii, July 8 to 11, 2016

Area Forecast Discussion
National Weather Service Honolulu HI
325 AM HST FRI JUL 8 2016

.SYNOPSIS...
Moderate to fresh trade winds will prevail through Saturday, with
light to moderate trade winds expected from Sunday into next week.
The trade winds will deliver clouds and showers to windward areas,
with showers most active during nights and mornings. A few showers
will spread leeward on the smaller islands, with the leeward Big
Island slopes seeing afternoon and evening clouds, and a few showers.
Hurricane Blas, now about 1700 miles east of the Big Island, is
forecast to rapidly weaken the next couple of days.

&&

.DISCUSSION...
High pressure far N of the area will continue to drive moderate to
fresh trade winds over the islands through Saturday, with lighter
trade winds expected from Sunday into next week. The lighter winds
are initially expected as a result of a weak low-level trough
(remnants of what once was tropical storm Agatha) passing from E to
W across the area, with the trough loosening the local pressure
gradient as it passes. Before winds diminish however, the approach
of the trough will cause trade winds to back to the NE, and a slight
tightening of the low-level pressure gradient, supporting locally
breezy conditions through Saturday.

The aforementioned trough is near 20N143W (about 800 miles E of the
Big Island) this morning, moving W near 10 mph. Meanwhile hurricane
Blas, currently about 1700 miles E of the Big Island, is moving WNW
toward cooler waters, and rapid weakening to a post-tropical remnant
low is anticipated by late this weekend. See the official forecast
from the National Hurricane Center for the latest on Blas.

In the short term, a fairly typical trade wind weather regime is
expected, with clouds and showers favoring windward areas, with
showers most active during nights and mornings. Latest satellite and
radar images indicate clouds and showers in greatest coverage over
near shore windward waters, with a decrease in clouds a little
further upstream. We can therefore expect a few morning showers to
give way to another warm afternoon with limited shower coverage.

Brief windward showers are anticipated tonight into Saturday, as the
atmosphere will be continue to be strongly capped between 6 and 8
kft. Increased moisture associated with the Agatha remnants may lead
to an increase in windward showers Saturday night into Sunday, with
winds veering to the E and weakening somewhat as the trough passes
Sunday night and Monday. Subtle differences continue to exist
between the GFS and ECMWF with this evolution, and while these
differences have some implications for the details of the sensible
weather forecast, we are not expecting significant weather impacts.

Early next week, the trade wind supporting high is expected to
weaken and shift E, while another low-level trough (remnants of
Blas) moves toward the islands in the prevailing trade wind flow.
Model differences are beginning to become less dramatic with this
portion of the forecast, with both the GFS and ECMWF now indicating
a light to moderate trade wind flow delivering brief windward
showers until the moisture associated with the remnants of Blas
arrives Wednesday and Thursday, likely fueling enhanced showers.
Most of this moisture is expected to affect windward areas, as some
semblance of trade wind flow is expected, although a weak low-level
trough is expected to accompany the slug of associated moisture.
After the remnants of Blas pass W of the islands around Thursday,
our attention will shift to the next tropical cyclone potentially
approaching from the E, which is currently identified as tropical
depression four-E about 3000 miles ESE of Hawaii. Much too soon to
have confidence in the details regarding that system and it's
potential affects, if any, on island weather.

&&

.AVIATION...
Clouds and showers upstream of Kauai, Oahu. and the Big Island have
thinned, so expect VFR conditions to prevail. Meanwhile, an area of
clouds and showers moving in on the trades will bring isolated areas
of MVFR to windward areas of Maui county over the next several
hours. Otherwise VFR conditions are expected to prevail through
today. An area of clouds upstream of the Big Island could bring some
MVFR conditions to the windward side of the island later today or
tonight.

&&

.MARINE...
A small craft advisory (SCA) for select marine zones around Maui and
the Big Island, where winds are most accelerated by island terrain,
has been extended through the day on Saturday. The expectation is
that trade winds will back to the NE tonight and Saturday, and
remain locally strong, as the pressure gradient is briefly tightened
by an approaching low-level trough that marks the remnants of what
once was tropical storm Agatha. Winds are expected to be below SCA
criteria statewide Sunday and Monday as the trough passes, with
winds potentially remaining below SCA speeds into the middle of next
week.

A new long-period S swell continues to build this morning, as
evidenced by observations at NOAA buoys 51004 and 51003, and a
PacIOOS buoy near Lanai, with the bulk of the swell energy currently
in the 16-18 second band. A high surf advisory for S facing shores
of all islands is now in effect through Saturday night, with surf
expected to diminish below advisory levels by Sunday. Long-period E
swells emanating from Hurricane Blas are expected to arrive later
today in Big Island waters, spreading W to the other islands through
Saturday as the swell builds. This swell is expected to be
relatively long-lived as the period gradually lowers through about
mid-week. A high surf advisory for E facing shores is likely to be
issued later today or Saturday. Toward the end of next week, another
long-period E swell is possible, if tropical depression four-E
intensifies and moves W as expected.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Sunday for south facing shores of
all islands.

Small Craft Advisory until 6 PM HST Saturday for Maalaea Bay-Pailolo
Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island
Southeast Waters.

&&

DISCUSSION/MARINE...Birchard
AVIATION...M Ballard