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fxhw60 phfo 220625 
afdhfo

Area forecast discussion
National Weather Service Honolulu HI
825 PM HST Fri Sep 21 2018

Synopsis...
high pressure to the north and aloft will maintain a stable trade
wind flow through Saturday night with clouds and showers favoring
the windward and mountain areas. A low will form northwest of Kauai
over the weekend and cause the winds to blow out of the southeast
and south starting Sunday. This flow will bring in not only some
humid weather but the potential for some unsettled weather to the
western end of the island chain that may last through the first
half of the new week.

&&

Discussion...
the trade winds are pretty much back, although there is slight
south component over Oahu and Kauai. We will remain under this
wind pattern through Saturday night. In the way of showers, radar
is pretty quiet, only a few specks around, favoring mainly the
windward and mountain areas. There are heavier showers, just to
the south and west of Niihau. It should stay off of Niihau.
The GFS solution is suggesting a somewhat drier than normal trade
shower pattern for the main islands, including the normally wet
windward Big Island through Saturday night.

Ridging aloft is helping put a lid over the islands with a low
level inversion at 5 to 7k feet area wide. This inversion is
expected to last through Sunday afternoon before breaking down due
to the deep trough nudging closer to the islands. So, expect
minimal shower activity over the weekend.

The latest GFS hint on the prolong rain to commence late Monday,
which is in line with the old European model (ecmwf) run. Periods of scattered
showers occur beforehand between Sunday and Monday mainly across
Kauai. We shall see if this outlook shifts in the ensuing model
runs. The unsettled weather can occur to other islands, not only
Kauai. It all depend on the low cloud moisture and where it is
located at. At a certain point, the forecast will likely include
a slight chance of thunderstorms.

One thing for sure, the south to southeast winds will
bring on a humid air mass to the islands that will likely last
through the first half of next week. We are expecting dew point
reaching into the mid 70s. The strength of the southeast/south
winds during this stretch is light to moderate.

Currently, an upper low is located 823 miles northwest of Kauai with the
trough extending southwestward. At the surface, is an inverted
trough, a reflecting of the trough aloft. It is a deep upper
trough with an extensive broken to overcast layer of mid and high
clouds, stretching eastward from the trough to the main Hawaiian
islands. Thunderstorms are noted some 260 miles west of Kauai. The
GFS is hinting on thinning these layered clouds on Saturday,
especially over the eastern half of the island chain.



&&

Aviation...
high pressure northeast of the state will keep a light to moderate
trade wind flow in place through Saturday. Low clouds and showers
will favor windward and Mauka areas, with some brief MVFR
cigs/vsbys possible here mainly overnight and during the early
morning hours Saturday. Predominantly VFR conditions are expected
at the taf sites through 23/06z.

No airmets are in effect and none are expected overnight.

&&

Marine...
high pressure northeast of the state will keep a moderate to
locally strong trade wind flow in place through Saturday. As a
result, a Small Craft Advisory (sca) remains in place for the
typically windy waters around Maui County and The Big Island. An
area of low pressure is expected to develop several hundred miles
northwest of Kauai over the weekend, allowing the winds to weaken
below Small Craft Advisory levels and shift around to the southeast Sunday through
early next week.

Surf will remain below advisory levels along all shores through the
middle of next week. Rough, short-period surf will remain around
the Summer average along east facing shores through tonight, then
decline over the weekend. A north-northwest is expected late next
week, which may bring moderate surf along north facing shores.
Background south swells will keep surf below average along south
facing shores through middle of next week. A small southwest
swell is possible late next week.

&&

Hfo watches/warnings/advisories...
Small Craft Advisory until 6 PM HST Saturday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island leeward waters-Big
Island southeast waters.



&&

$$

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