Flash Flood Warning 58, NWS Honolulu, HI

Area Forecast Discussion
National Weather Service Honolulu HI
400 AM HST Thu Sep 13 2018

.SYNOPSIS...
A low aloft north of the islands will pass northwest of Kauai later
today. Instability from this low combined with moisture from Olivia
will keep the weather unsettled across the state through late
tonight. A drier and a little more stable airmass will spread across
the islands over the weekend, with seasonal trade wind weather
returning.

&&

.DISCUSSION...
Rather wet weather continues to affect much of the islands early
this morning as moisture associated with Olivier is still present
over much of the islands. Meanwhile, a low aloft north of the
islands is moving southwest and will pass northwest of Kauai later
today, providing atmospheric instability to the area. Both early
morning Lihue and Hilo soundings depicted a rather moist and
unstable airmass with higher precipitable water values compared to
Wednesday afternoon. This resulted in rather active weather for much
of the islands, with a few thunderstorms developed near Molokai and
Oahu overnight. Winds have decreased much across Oahu and Kauai since
last night. Thus wind advisory for those islands have been cancelled.

Expect unsettled and wet weather to persist across the state today
and tonight, with the threat of heavy rain continuing. Have
increased the coverage of chance of thunderstorms to much of the
state in this forecast package today, since it is hard to pin point
where the thunderstorms may flare up. The heaviest rain will still
likely affect the western islands today. A Flash Flood Watch remains
in effect for all islands through late tonight.

Latest forecast solutions still indicate a drier as well as a more
stable airmass spreading to the islands beginning Friday. Meanwhile,
a surface high will prevail far north of the islands, providing
trade winds to the state. Therefore, seasonal trade wind weather is
expected to return to the islands over the weekend into early next
week.

The latest Olivia Forecast Advisory from Central Pacific Hurricane
Center is available at weather.gov/cphc

&&

.AVIATION...
Tropical Depression Olivia, roughly 220 miles southwest of Kauai,
continues to move westward away from the Hawaiian Islands this
morning. Deep tropical moisture associated with Olivia will linger
over the islands today with enhanced showers and scattered MVFR
ceilings favoring windward and mountain areas of each island.
Expect lesser shower coverage and higher cloud ceilings forecast
over leeward areas of each island. A few thunderstorms will also
develop today across the state.

AIRMET SIERRA for mountain obscuration continues for all island
mountains and north through east sections. The coverage for AIRMET
SIERRA will decrease later this morning.

AIRMET Tango remains in effect for strong winds producing
moderate low level turbulence over and south through west of
mountains over all islands.

&&

.MARINE...
For the latest on Olivia, please monitor the forecast and
advisory packages from the Central Pacific Hurricane Center.

Swell from Olivia is quickly dropping off this morning. The High
Surf Warning (HSW) for Oahu and the High Surf Advisory (HSA) for
Maui County and the Big Island have been cancelled. There is just
enough residual energy within the fading east swell to keep the HSA
up for Kauai through today.

A small northwest swell is expected to peak today. A small south
swell is likely over the weekend, with another small northwest swell
expected late in the weekend and early next week.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through late tonight for all Hawaiian islands.

High Surf Advisory until 6 AM HST early this morning for Kauai
Windward.

Small Craft Advisory until 6 PM HST this evening for all
Hawaiian waters.

&&

DISCUSSION...Hui
AVIATION...Bohlin
MARINE...Powell