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RH14 %
WindWNW 1 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

420
FXHW60 PHFO 251331
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
331 AM HST SUN SEP 25 2016

.SYNOPSIS...
Trade winds will strengthen today and Monday, and will be locally
breezy for The upcoming week. While a drier than normal trade wind
weather pattern is expected today and tonight, a short-lived
increase in trade showers is expected early Monday. Beyond that, a
typical trade wind weather pattern is expected this week, with
clouds and brief showers favoring windward slopes and coasts, mainly
during nights and mornings. While leeward areas will be mostly dry,
leeward Big Island will see afternoon and evening clouds, and a few
showers.

&&

.DISCUSSION...
A stable trade wind pattern is over the islands this morning, with
just a few showery low clouds approaching the islands from the E.
High pressure currently building to the distant NW of the islands is
supporting increasing trade winds, and will be the primary surface
feature driving island weather this week as it tracks steadily
eastward.

While a drier-than-normal trade wind weather pattern is expected
today and tonight, a short-lived increase in trade wind showers is
anticipated early Monday. This is expected as an area of low-level
moisture associated with a weak mid-level trough, still about 500
miles E of the islands, arrives on the trade wind flow. While this
will bring an increase in mainly windward showers, significant
rainfall accumulations are not expected.

The high passing well N of the area will support locally breezy
trade winds, and a typical trade wind weather pattern will prevail
from later Monday through at least Friday, with clouds and showers
over windward areas most active during nights and mornings. Heading
into next weekend, the GFS and ECMWF are somewhat consistent in
depicting an increase in moisture arriving from the E and SE,
despite some differences in their depiction of synoptic features.
Using a blend of these solutions, the long-term forecast grids
were modified to increase PoPs next weekend.

&&

.AVIATION...
Trade winds in the light to moderate range will strengthen today as
a strong surface high far northwest will move to far north of the
state in the next few days. Expect windward sections of the islands
to see some MVFR ceilings at times as the trades bring low clouds
with embedded showers to the area. Lee areas of the Big Island may
also see brief MVFR ceilings this afternoon. Otherwise, VFR
conditions will prevail for most areas.

Increasing trade winds may lead to the issuance of AIRMET TANGO for
turbulence later today.

&&

.MARINE...
A high pressure cell building to the distant NW of the islands is
bringing an increase in trade wind speeds, and an overnight ASCAT
pass indicated winds up to 25 kt in the Alenuihaha channel. With
winds expected to increase further, a Small Craft Advisory (SCA) has
been issued for the typically windy marine zones around the Big
Island and Maui. The SCA is posted through Tuesday night, although
it is expected that it will need to remain in place through much of
the week.

Surf will be small, especially by Hawaii standards, through the next
week. A series of mainly small pulses of SSW swell will continue to
bring small surf to S facing shores. A very small, relatively short-
period NW swell is already diminishing and this swell will fade
today. A new relatively short-period NNW swell is expected Monday
and Tuesday, but resulting surf along N and W facing shores will be
small. Increasing trade winds will lead to gradually increasing wind
waves that will drive moderate short-period surf along E facing
shores.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 AM HST Wednesday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

&&

$$

DISCUSSION/MARINE...Birchard
AVIATION...Hui

Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office