Heavy Rain in Hawaii, February 12 to 14, 2018

Area Forecast Discussion
National Weather Service Honolulu HI
353 PM HST Mon Feb 12 2018

.SYNOPSIS...
An approaching front is expected to reach Kauai Tuesday afternoon,
then slowly drift east and stall over the eastern part of the
island chain on Thursday. A couple of upper level disturbances will
aid in keeping the air mass unsettled during the rest of the week,
especially across the eastern part of the state.

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.DISCUSSION...
The low level wind flow is gradually becoming southerly over the
western half of the island chain this afternoon, with isolated
pockets of low level moisture forming and dissipating. One such
pocket has moved ashore on Kauai, while another one is threatening
the south shores of Oahu. The forecast calls for a few late
afternoon showers over the interior and leeward areas of these two
islands. The showers will dissipate early in the evening, but
there will be more showers forming under this convergent southerly
flow overnight and into Tuesday, resulting in a chance of showers
for all of the smaller islands. The Big Island may avoid all of
these clouds and showers tonight and Tuesday before turning sour.

The ECMWF and GFS models are slowing down the front, with the
front now reaching Kauai early Tuesday afternoon. The front is
slated to weakening to a trough, draped across Oahu Wednesday
afternoon. The trough eases into Maui county and the Big Island
between Wednesday night and Thursday before stalling once again.
A surface low is indicated by both models near 27N164W, roughly
400 miles NW of Kauai on Wednesday afternoon. Both models are
also pointing to an extended period of unsettled weather lingering
into the upcoming President's Day weekend mainly across the Big
Island, which is aided by another, perhaps stronger, upper level
impulse. It is uncertain where the most threatening weather will
be, but it appears to be the eastern part of the island chain at
this time. Precipitable water values are expected between 1.5 and
1.7 inches across Maui and the Big Island between Thursday night
and Friday night. Not very high values but worth watching out
for this area of weather is stationary.

The surface wind field east of the front has been adjusted up
toward small craft advisory criteria between Tuesday and
Thursday particularly the windward waters of Maui and the Big
Island and waters south of the Big Island. Confidence is low
with the existing wind field after Thursday.

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.AVIATION...
Light southeasterly in advance of an approaching cold front
continues to spread ragged clouds and isolated showers across the
state this afternoon. Clouds will thicken through the evening
hours and shower activity increase after midnight once the front
nears Kauai.

Isolated MVFR conditions expected in showers, otherwise VFR
conditions will prevail all areas. MVFR Ceilings may become more
numerous after midnight, possibly necessitating an AIRMET for
mountain obscuration on Kauai or Oahu late tonight or Tuesday
morning.

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.MARINE...
Winds will be from the south and southeast across the islands as
a front slowly approaches from the northwest. The front is
forecast to reach Kauai Tuesday afternoon, then continue slowly
eastward through the week before stalling and weakening around
midweek. Winds behind the front will shift from the west. Surface
winds have been adjusted upwards toward SCA criteria over the
windward waters of Maui and the Big Island and waters south of
the Big Island between Tuesday and Wednesday night. An area of
strong trades east of the islands could push seas to near SCA
levels later this week.

A moderate northwest swell will increase across the islands
through Tuesday, with surf approaching advisory levels along
north and west facing shores Wednesday, as well as seas possibly
reaching small craft advisory level near Kauai Tuesday night into
Wednesday.

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.HFO WATCHES/WARNINGS/ADVISORIES...
None.

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AVIATION...Bedal
MARINE...TS
REST OF DISCUSSION...Lau