Drought in Hawaii, November 1 to 14, 2017

Area Forecast Discussion
National Weather Service Honolulu HI
848 PM HST Tue Oct 31 2017

.SYNOPSIS...
A stalled front will remain to the northwest of Kauai through
Wednesday. Abundant moisture and instability will keep the
potential for thunderstorms and flooding rains over Kauai, with
humid conditions statewide, overnight and Wednesday. The front
will slowly dissipate and drift westward away from the area
Wednesday night and Thursday, with the atmosphere gradually
stabilizing over the state. Increasing trade winds will build
across the islands beginning around Thursday night and continuing
into the weekend.

&&

.DISCUSSION...
Active weather prevails across the far western and far eastern
ends of the state on this final evening of October, with much more
quiet conditions in between. Earlier heavy rains over Kauai caused
flooding on the Hanalei River at Kuhio Highway early this evening,
but these rains have diminished across the island during the last
couple of hours. Meanwhile, an area of heavy rains and even an
isolated thunderstorm has moved into the Puna district of the Big
Island during the early evening. Dry weather prevails this evening
over Oahu, Maui County and the remainder of the Big Island. To the
southwest and west of Kauai, showers have increased recently over
the waters and across Niihau.

Surface analysis depicts a stalled front about 300 miles west-
northwest of Kauai. Weak high pressure lies far northeast of the
state. The flow pattern between these two features veers from ESE
over the Big Island to southerly over Kauai. Satellite imagery
shows a vertically stacked low from the surface to aloft located
about 1100 miles northwest of Kauai. This low is nearly
stationary. Pre-frontal convergence bands are generating heavy
showers and scattered thunderstorms over the offshore waters
northwest of Kauai, but this activity is making little eastward
progress at the moment. MIMIC-TPW imagery shows a moist airmass
over the state, with estimated PW values in excess of 2 inches
across Kauai. The 00Z soundings also reflect this, with the Lihue
sounding showing no inversion and PW of 2.04 inches, while the
Hilo sounding shows only a very weak inversion near 8000 feet and
PW of 1.55 inches.

Overnight, the most active weather will likely remain across
Kauai and eastern parts of the Big Island. The flash flood watch
remains in effect for Kauai and Niihau, where locally heavy rains
and isolated thunderstorms will remain possible. The forecasts
have been updated to reflect this, and to lower rain chances for
the remainder of this evening across Oahu.

Wednesday looks like a potential repeat of today, with a humid
airmass remaining in place under light south to southeasterly
flow. The threat of flash flooding will remain over Kauai through
the day. For the rest of the state, weak ridging at the surface
and aloft will partially counteract afternoon heating and moderate
moisture/instability, with a chance of continued interior showers
and possibly even an isolated thunderstorm statewide Wednesday
afternoon.

A surface ridging building in north and northeast of the area on
Thursday will force the dissipating front further to the west of
our area. The ridge will also result in strengthening trade winds
beginning around Thursday night, which are expected to continue
through the weekend. A building ridge aloft should provide more
stable conditions, although lingering low level moisture may
provide a rather showery trade wind pattern for windward and mauka
areas into the weekend. Longer range models show a significantly
drier airmass moving into the state from the east beginning on
Sunday and remaining in place into next week. This airmass change
combined with continued ridging aloft should produce a rather dry
trade wind pattern during that time.

&&

.AVIATION...
Southerly winds will persist across the island chain through
Wednesday, bringing moist and unstable air to the area, as a surface
front remains stationary northwest of Kauai. The western end of the
state will likely see the most unsettled weather, though the
potential for locally heavy rain and a slight chance of
thunderstorms still exists for much of the islands through early
Wednesday.

AIRMET SIERRA for mountain obscuration remains in effect for Kauai,
and may extend to the other islands if conditions warrant.

&&

.MARINE...
Heavy showers and thunderstorms associated with a cold front and
broad upper low positioned west-northwest of the state will
continue to impact portions of the waters into midweek. The best
chance for thunderstorms will remain over the Kauai waters through
this time. Trade winds and drier air are expected to return
through the second half of the week and into the upcoming weekend
as high pressure builds north of the region and the stalled cold
front shifts away from the islands.

The local winds are forecast to remain out of the southeast in the
light to moderate range through midweek, then increase into the
fresh to strong category Friday through the upcoming weekend as the
trades return. Small craft advisory conditions will become a
possibility across the typically windier channels between Maui
County and the Big Island beginning Friday.

After a jump start to the winter season along north and west facing
shores last week through this past weekend, surf is expected to
remain around and below average through the upcoming weekend. The
largest surf through this forecast period is expected late tonight
through Wednesday as a medium sized west-northwest (310-330 deg)
swell continues to fill in. Breakers will likely reach advisory
levels (15 ft faces) on Kauai and remain below along exposed coasts
from Oahu to the Big Island as the swell builds down the island
chain.

Observations at the offshore buoys northwest of Kauai quickly ramped
up through the day today and have climbed a couple of feet above
WAVEWATCH III this evening, which is more in line with the ECMWF-
Wave solution that shows a peak at 11 ft. The bulk of this energy is
coming in within the 13-14 sec bands. This upward trend is expected
at the nearshore PacIOOS buoys overnight as the swell fills in.

A long-period west-northwest (310-320 deg) swell associated a
hurricane-force low that developed near the Kuril Islands this past
Monday as Typhoon Saola lifted north and became extratropical is
expected to fill in late Thursday night and hold into the weekend.
Although ASCAT passes over this fetch region showed a large area of
gale- to storm-force winds focused toward the islands, this fetch
area was limited due to the Kuril Islands. As a result, surf
should peak well below the November average Friday.

Surf along east facing shores will begin to rise Friday through the
upcoming weekend as the trades return and strengthen locally and
upstream of the islands.

South along south facing will remain small through the weekend
with mainly small background long-period energy expected. For the
outlook, guidance depicts a decent sized batch of gale- to storm-
force southerly winds focused toward the islands within 170-180
deg band tonight into Wednesday located around 1500 NM east of New
Zealand. WAVEWATCH III depicts a long-period south (170-180 deg)
swell filling in locally Tuesday night into Wednesday (2-3 ft) of
next week.

For more detailed information on the surf for Oahu, see the latest
collaborative forecast at: www.prh.noaa.gov/hnl/pages/SRF.php

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Wednesday afternoon for Niihau-Kauai.

High Surf Advisory until 6 PM HST Wednesday for north and west
facing shores of Niihau and Kauai.

&&

DISCUSSION...Jacobson
AVIATION...Hui
MARINE...Gibbs

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HONOLULU HI
701 PM HST TUE OCT 31 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0630 PM     FLOOD            HANALEI                 22.21N 159.50W
10/31/2017                   KAUAI              HI   EMERGENCY MNGR

            KAUAI EMERGENCY MANAGEMENT AGENCY REPORTS THAT KUHIO

            HIGHWAY AT THE HANALEI BRIDGE IS CLOSED TO ROAD FLOODING.

&&

JACOBSON

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HONOLULU HI
701 PM HST TUE OCT 31 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0630 PM     FLOOD            HANALEI                 22.21N 159.50W
10/31/2017                   KAUAI              HI   EMERGENCY MNGR

            KAUAI EMERGENCY MANAGEMENT AGENCY REPORTS THAT KUHIO
            HIGHWAY AT THE HANALEI BRIDGE IS CLOSED TO ROAD FLOODING.

&&

JACOBSON