Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 152005
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
1005 AM HST Wed Aug 15 2018

.SYNOPSIS...
Light to moderate trade winds will prevail during the next few
days. Moisture moving in from the east will produce an increase
in humidity and windward rainfall across the eastern half of the
island chain today, with afternoon clouds and spotty showers over
leeward terrain on the Big Island and Maui. The increase in
humidity and shower activity will spread to Oahu tonight then
Kauai by Friday. A larger increase in humidity and shower activity
is due this weekend, as another area of moisture moving along the
increasing trade wind flow. Breezy and drier trade winds are
expected on Monday.

&&

.DISCUSSION...
Trade winds are down a notch, but shower activity is trending up
across portions of the state. Trades have dropped mainly into the
gentle to moderate range as the pressure gradient between the
islands and a 1026 mb surface high far northeast has weakened.
After relatively dry conditions during the past couple of days, a
pocket of low level moisture in the trade wind flow has moved onto
windward slopes of the Big Island and Maui County, leading to an
increase in windward rainfall this morning. An upper level trough
extending from an upper low centered several hundred miles to the
northeast has weakened the inversion over the state and is sending
thin bands of high clouds overhead.

The gentle to moderate trade wind flow will maintain wetter
conditions over the eastern half of the state today. Windward
slopes of the Big Island, Maui, and Molokai will continue to be
rather wet as the pocket of enhanced moisture remains in place,
and windward portions of Oahu and Kauai will experience limited
shower activity. Sea breezes will overpower the trade wind flow
across sheltered leeward areas. This will mean spotty showers
afternoon showers over leeward and interior Big Island and Maui,
and with the inversion eroded, a few showers could be briefly
heavy, especially on the Big Island. Thin high clouds will
continue to stream overhead.

For Thursday and Friday, trade winds will remain unchanged in the
gentle to moderate range as humid and slightly wet conditions
linger. Windward slopes will be see the bulk of the rainfall, but
as sea breezes take over each afternoon, leeward areas will
experience clouds and spotty showers. A few of these showers could
be heavy across leeward Big Island. Conditions will also be
somewhat humid as dew points creep up into the lower 70s.

Trades will be up a notch but so will humidity and shower
activity this weekend. A pocket of tropical moisture will be
moving along the moderate trade wind flow. This will likely drive
dew points up into the mid 70s, leading to a noticeable increase
in humidity. Showers will continue to favor windward slopes, while
afternoon sea breezes produce afternoon clouds and spotty showers.
With precipitable water values reaching as high as 2 inches, some
afternoon showers could be briefly heavy. This will continue to be
more prevalent on the Big Island, where thunderstorms will be
possible.

Drier and more stable trade wind weather is expected on Monday.

&&

.AVIATION...
Most areas will maintain relatively moderate trade wind speeds
today, and that should continue into Thursday. Should not have
strong enough winds to warrant an AIRMET for low level turbulence.
Most shower activity will be confined to the windward side of the
Big island as well as a few light showers on the windward slopes
of the other islands so expect scattered areas of MVFR conditions
for the windward slopes, especially on the Big Island and VFR
conditions elsewhere.

There are no AIRMETs currently in effect for Hawaii today and we
do not anticipate ant through the period.

&&

.MARINE...
Light to moderate trade winds are expected to continue into the
weekend, with winds expected to remain below Small Craft Advisory
levels. Shower activity is expected to increase this weekend,
particularly over the windward waters as remnant tropical
moisture moves in from the east.

No significant swells are expected over the next several days, so
expect surf to remain small on all shores. A small south-
southeast swell is expected to fill in Thursday, peak Friday and
hold through Saturday at heights below the summer average. No
significant seas are expected into early next week.

See the latest Oahu Surf Discussion (SRDHFO) for more details on
surf and swell.

&&

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

&&

$$

DISCUSSION...Wroe
AVIATION...Chevalier
MARINE...M Ballard


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