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Temp6.6 C
RH22 %
WindWSW 17 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

668
FXHW60 PHFO 230158
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
358 PM HST Fri Sep 22 2017

.SYNOPSIS...
Trade winds will gradually trend down over the weekend as the
ridge of high pressure to the north weakens and a weak surface
trough slowly approaches from the northeast. Mainly windward
clouds with light passing showers will prevail into early next
week, with a possible boost in shower activity around the middle
of next week.

&&

.DISCUSSION...
A weakening 1028 mb high is currently positioned far northeast of
the area this afternoon and driving moderate trade winds over the
islands. An upper low northeast of the area is also inducing a
weak surface trough, though it is having little impact on our
weather now.

Satellite-derived precipitable water imagery and upper air
soundings at Lihue and Hilo reflected values between 1.2 to 1.4
inches. Visible satellite shows a few windward and mauka clouds
with mostly sunny skies leeward. Radar shows very little
precipitation blowing in with the trade winds this afternoon.

Trade winds are expected to trend down to gentle to moderate
breezes over the weekend as the high to the far northeast weakens
and the surface trough edges closer. Mostly dry and stable trade
wind weather will continue each day with clouds and showers
favoring windward locations. Rainfall accumulations will be light,
with precipitable water values holding in the 1 to 1.3 inch range
(near to below average) through the weekend and Monday.

The GFS and ECMWF both depict the surface trough approaching the
islands from the east by midweek. The weak trough, combined with
a slight increase in moisture, may be enough to bring the rain
chances back to normal over windward locations Tuesday and
Wednesday. Meanwhile, trade winds will remain in the gentle to
moderate range until the weak surface trough reaches the state the
middle of next week.


&&

.AVIATION...
High pressure north-northeast of the State will keep a moderate
trade wind flow in place through tonight. Clouds and showers will
favor windward and mauka areas, with isolated spillover showers
trickling over into leeward areas from time to time. Brief MVFR
cigs/vsbys in showers, otherwise prevailing VFR conditions
expected all areas.

AIRMET Tango remains in effect for low level turbulence over and
downwind of the terrain of all islands. This AIRMET will likely
remain in place through at least the evening hours.



&&

.MARINE...
Fresh to locally strong trades should gradually weaken later today,
decreasing wind speeds into the light to moderate range through
the weekend. Trade winds will continue to bring rough surf along
east facing shores today, easing this weekend.

Surf along south facing shores will remain small through early next
week, with mainly background southeast and southwest swell energy
expected. The next potential long-period pulse out of the
southwest from the Tasman Sea is expected by Sunday and could
lead to a slight increase in surf. For the extended forecast,
strong to gale-force southwest winds associated with a low in the
Tasman Sea may lead to another small southwest swell Tuesday
through midweek.

A small northwest swell will continue into the weekend before
easing. Another small reinforcement from that direction is
expected to fill in around Sunday night through the middle of next
week.


&&

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

&&

$$

DISCUSSION...Foster
AVIATION...Bedal
MARINE...TS

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