Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 191410

Area Forecast Discussion
National Weather Service Honolulu HI
400 AM HST Sat Aug 19 2017

Light to locally moderate winds will prevail across the islands
through early next week as a high ridge far north weakens. The
lighter winds will allow local sea breezes to be more prominent
across leeward areas, with an increase in clouds and showers each
afternoon and evening. Meanwhile, low clouds carried by the trades
will still continue to affect windward and mauka areas at times.
Tropical moisture from the east will bring an increase in shower
coverage and muggy conditions to the state late Saturday through
early Tuesday. Expect drier and windier conditions to return by the
second half of next week as a stronger high pressure rebuilds far


Light trade winds prevail across the islands early this morning as
high pressure ridge far north weakens. Area of low clouds that
affected windward Big Island last night has spread to Maui and
Molokai overnight, providing more showers to windward areas of those
islands. Elsewhere there are still low clouds embedded in the trade
wind flow, reaching windward areas and bringing some showers there.
Early morning Hilo sounding revealed a more moist and still slightly
unstable airmass. That`s not surprising considered the clouds in the
windward Big Island vicinity since last night. Latest satellite
imagery showed there are some breaks in the clouds upstream just
east of the islands, and those clouds may decrease a little more
under daytime heating.

Trade winds will remain in the light to locally moderate level for
the rest of the weekend into early next week. as pressure gradient
further relaxes across the region. This will allow sea breezes to
develop more fully over the lee areas, with clouds and showers
during the afternoon and evening. Meanwhile, low clouds carried by
the lighter trade winds will continue to affect windward areas at

An upper level trough just north-northeast of the islands will shift
more west and deepens in the coming days. Airmass in the island
vicinity will slowly become more unstable, allowing low clouds in
the area to be enhanced. In addition, tropical moisture is expected
to reach the islands beginning tonight into Sunday, then linger
through early part of next week. Look for increased shower coverage
across the islands, especially windward areas, with an overall muggy
feel to the air tonight through Tuesday. Believe the airmass will be
unstable enough for a slight chance of thunderstorms over the
northwest coastal waters Sunday night through early Tuesday. This
most likely will be revised as the event unfolds through the next
few days.

Forecast models still indicate possible weather improvement for the
island towards later part of next week as the upper level feature as
well as the tropical moisture exit the state west. A surface high
is expected to rebuild far north of the islands, with trade winds
possibly increasing back into the moderate to even breezy range.


A ridge of high pressure north of Hawaii will keep moderate strength
trade winds in the forecast today. Mostly VFR conditions are
forecast with periods of MVFR ceilings over mountains and northeast
slopes of all islands. Expect numerous shower coverage along
northeastern windward slopes with scattered showers elsewhere.

AIRMET Sierra for Tempo Mountain Obscuration in effect over windward
Big Island and Maui.


Winds and seas are expected to remain below Small Craft Advisory
levels through the weekend as the pressure gradient weakens. An
upper low that is expected to drift southwest over the region may
lead to better shower coverage later in the weekend over portions of
the marine area, and could even produce a few thunderstorms Sunday
night into early next week. Wind speeds will increase again later
next week.

Surf along south facing shores will steadily lower through the day
as a south-southeast swell that filled in and peaked on Friday
eases. The latest observations at 51003/51002/51004 south of the
islands reflect this downward trend and depict most of the remaining
energy within the 14-15 sec bands. Looking ahead into next weekend,
mainly small background reinforcing pulses out of the south will
keep the surf from going flat each day.

Surf along east facing shores will remain small into next week due
to weaker trades locally and upstream of the state. Although
confidence remains low this far out, a small long-period east (090
deg) swell from distant Tropical Storm Kenneth, currently centered
over the eastern Pacific, could fill in and impact exposed eastern
shores through the middle to latter half of next week.

Water levels are running around 7 to 8 inches above the predicted
levels due to a sea surface height anomaly associated with an
oceanic eddy moving through the islands from east to west. This
combined with the normal King Tide will result in coastal flooding
in the vulnerable low-lying coastal locations each day through the
weekend. Flooding will be expected through the afternoon hours each
day through the weekend around the peak daily high tide cycles. The
peak of this event is expected Saturday afternoon, when total waters
levels will likely top what was observed in Honolulu at the end of
April earlier this year. See the Special Weather Statement, SPSHFO,
for more details.





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