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Hawaiian Islands Synoptic Discussion and Guidance

927
FXHW60 PHFO 291937
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
937 AM HST FRI JUL 29 2016

.SYNOPSIS...
A surface high to the north will keep trade winds blowing over the
islands through the coming week. The trades will carry areas of
tropical moisture over the islands while a passing low aloft will
make the atmosphere unstable. This combination will keep the
weather rainier than normal over much of the next week.

&&

.DISCUSSION...
A 1032 MB surface high 1600 miles north northeast of Honolulu at
43N149W will move slightly to the west with little change in
strength through tomorrow. The pressure gradient southwest of the
high will keep breezy trade winds blowing over the main Hawaiian
Islands through this evening. Balloon soundings at 200 AM showed
a strong temperature inversion sloping from 5200 feet at Lihue to
6600 feet at Hilo. This inversion will limit cloud growth and keep
rainfall light today.

Water vapor imagery shows a low aloft 740 miles east northeast of
Honolulu at 25N147W moving toward the west northwest around 20
mph. As this low moves by the islands tonight through early next
week, it will weaken the trade winds and raise the temperature
inversions. The higher inversions will mean that the trade wind showers
will become more active. Radar shows the shower activity has
already increased across the state this morning, and we should
continue to see the increasing trend tonight. Most of the rain
focused over the typical windward and mauka areas, but leeward
areas will also see occasional passing showers over the next few
days.

Next Tuesday, the low aloft moves north away from the islands and
the trade winds will become breezy again through the remainder of
the week. A drier airmass will carry in with the trades about that
time, so less showers are expected on Tuesday into the Wednesday
afternoon. Showers will increase again Wednesday night as another
plume of moisture moves in with the trade winds.

&&

.AVIATION...
AIRMET TANGO for low level turb over and S through W of the
mountains remains posted as breezy NE to E trade winds continue.
The 12Z soundings from PHTO and PHLI show a strong inversion
between 5 and 8 thousand feet.

Expect primarily VFR conditions with isolated MVFR conditions
along the windward slopes and over windward waters as trades
bring in low clouds and showers from the east.

&&

.MARINE...
A high to the northeast will maintain strong to near-gale force
trade winds across the area today. A Small Craft Advisory (SCA) is
in effect for all Hawaiian waters through this evening. Winds will
taper off as a weak surface trough arrives from the east tonight
into Saturday. Some or all zones may drop out of the SCA this
weekend. The trade winds will strengthen again by the middle of next
week.

The trade winds will produce choppy surf along east facing shores
during the breezy time periods as mentioned earlier, but surf is
expected to remain below advisory levels over the next week.
There will be a series of small south swells into next week but
surf will remain below the advisory level along south facing
shores as well. Only small surf is expected along north and west
facing shores.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST this evening for all
Hawaiian waters-

&&

$$

DISCUSSION/MARINE...Foster
AVIATION...Morrison

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