Flash Flood Watch 6, NWS Honolulu, HI

Area Forecast Discussion
National Weather Service Honolulu HI
455 PM HST Wed Mar 14 2018

.UPDATE...
A Flash Flood Watch has been issued for Kauai and Niihau. Persistent
rain over and southwest of Kauai will allow for the possibility
of flash flooding through tonight. Streams are already running
high and soils are saturated.

&&

.SYNOPSIS...
Mostly cloudy skies can be expected over the next couple of days
thanks to an area of low pressure west of the area. Numerous
showers can be expected over the west end of the state through
Thursday with scattered showers possible over the remainder of the
state. Shower activity is expected to become less active Friday
through the weekend with passing showers possible over windward
and mauka areas as well as some possible showers over interior
areas during the afternoon hours. Another round of wet weather is
possible beginning around Tuesday as another area of low pressure
moves closer to the state from the west.

&&

.DISCUSSION...
An area of low pressure is centered several hundred miles west of
the area. A deep layer of tropical moisture is being drawn
northward on the east side of the low. Mostly cloudy skies are the
result. Radar shows most of the shower activity is presently over
and around Kauai with lessor amounts of showers over the remainder
of the state mainly affecting windward and mauka areas. For the
most part, showers are expected to be light to locally moderate in
intensity though a few brief heavy showers can't be ruled out
especially over Kauai. This general weather pattern is expected to
continue through Thursday as the area of low pressure gradually
moves northward west of the area.

The low level wind flow is currently from the east southeast.
However as the low moves northward over the next couple of days,
winds will turn more to a southeasterly direction especially over
the west end of the island chain. This wind pattern will continue
on into Saturday. Showers will tend to favor windward and mauka
areas as well as some interior areas during the afternoon hours.

As we start the new week, another area of low pressure is forecast
to move eastward closer to the state. Low level wind flow over the
west end of the state will swing around to a southerly direction
while remaining from the east southeast near The Big Island. The
global models are in good agreement in keeping the bulk of the low
precipitation field west of the area Monday. However daytime heating
along with low level moisture convergence may allow for some showers
to move over the islands especially the west end of the chain. Rainfall
chances look to increase Tuesday and Wednesday over the west end of
the state as the lows associated frontal boundary approaches Kauai
from the west.

&&

.AVIATION...
A SFC low about 430 miles WSW of Kauai will continue to gradually
push N. The associated warm front will pass over the island chain
this evening and overnight and continue to bring the chance for
rain to all islands. Winds will begin to veer SE tonight into
tomorrow.

AIRMET Sierra remains in effect for mountain obscuration across
Kauai and windward sections of Oahu, Molokai, Maui, and the Big
Island. These conditions will likely continue into tonight.

AIRMET Zulu remains in effect for moderate icing over Kauai. These
conditions are expected to remain in place into tonight.

&&

.MARINE...
The latest ASCAT pass failed to show any 25 kt winds in the
channels or other windy areas. Also, a surface low about 430 nm
west-southwest of Kauai is forecast to drift slowly northward far
west of Kauai over the next couple of days, causing the winds to
become southeast and weaken across the state tonight through
Friday. As a result, the Small Craft Advisory has been dropped for
all areas. Light winds are expected to continue across the area
this weekend as the low tracks north of the region.

Rough surf conditions have begun to decline along east facing
shores and have lowered enough that the High Surf Advisory has
been cancelled for those areas. The east swell will continue to
slowly subside tonight through the weekend as the winds weaken and
become southeast. The current north swell will also continue to
decline through the end of the work week.

Small north and northwest swells arriving this weekend are
expected to produce slight bumps in surf along some north and west
facing shores of the smaller islands from Saturday through early
next week, but remain below advisory level.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through late tonight for Niihau-Kauai.

Winter Weather Advisory until 6 AM HST Thursday for Big Island
Summits.

&&

Synopsis/Discussion...Burke
Aviation...Chevalier
Marine...TS