Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 290200

Area Forecast Discussion
National Weather Service Honolulu HI
400 PM HST Sun May 28 2017

Light winds will prevail through the holiday weekend, allowing
for a few windward showers during nights and mornings, with clouds
and showers shifting to leeward and interior areas in the
afternoons. The island atmosphere will be a little unstable today,
which will allow some showers to become briefly heavy. Light to
moderate trade winds on Tuesday and Wednesday are expected to
become breezy by the end of the week. The trade winds will bring a
few brief windward showers, with mostly dry conditions leeward,
as a more seasonable weather pattern develops.


Surface troughs NW and E of the state have interrupted island
trade winds, bringing variable winds with daytime sea breezes and
nighttime land breezes over the islands. This trend will continue
through Memorial Day. Without the cooling trades, sensible weather
will be hot and humid during the day with cooling temperatures at
night. Current afternoon conditions are partly to mostly cloudy
skies with sea breezes, and land heating creating rising motion
over interior areas. The Big Island has seen the heaviest showers
this afternoon with isolated thunderstorms forming upslope of Hilo
and along the Hamakua Coast. Any lingering thunderstorm and heavy
shower activity should diminish this evening as the sun sets and
the islands cool.

An upper level trough now over the eastern end of the state has
brought some instability to the atmosphere. The soundings from
Hilo shows a jump in atmospheric instability with ML CAPE
increasing from 311 J/kg early this morning to 1149 K/kg this
afternoon. This instability weakened our normally cloud capping
temperature inversion, and allowed for the aforementioned
thunderstorms to form in conjunction with the peak land heating.
The upper trough and instability will move steadily northeast
tonight allowing a more stable atmosphere to move over the Aloha
state tonight and tomorrow. For Memorial Day, expect clear skies
in the morning with clouds and isolated showers during the
afternoon. With the more stable atmosphere, any showers that do
occur will carry only light to moderate rainfall.

High pressure will build north of the state Monday night and
Tuesday bringing back our normal trade winds with windward and
mountain showers expected through the rest of the week.


A weak high pressure ridge north of the Hawaiian Islands will
continue to produce weak easterly trade winds through Monday
allowing onshore sea breezes to develop over each island during
the day with offshore land breezes at night. Cloud ceilings and
scattered showers will develop over island interiors by afternoon
with brief periods of MVFR conditions forecast through the early
evening hours. Land breezes overnight will tend to clear out cloud
cover over each island by the early morning hours.

An upper level low currently over the Big Island will continue to
drift eastward away from the state over the next 24 hours.
Unstable air with this low will continue to produce thunderstorm
activity over the Big Island through 03Z. Cloud tops will range
from 10-15kft across the islands with CB cloud tops up to 30kft.

AIRMET Sierra in effect for mountain obscuration on the eastern
slopes of the Big Island until 0400Z.


Surf along the south facing shores has dropped below advisory
levels, so the High Surf Advisory has been cancelled. Although the
surf is on the decline, it will remain elevated and will
contribute to coastal flooding.

Actual tides at Honolulu continue to arrive about 0.5 feet above
predicted level. High tides today and tomorrow are predicted to be
over 2 feet, and just under 2 feet on Tuesday at Honolulu. The
combination of king tides and the south swell continues to bring
the likelihood of coastal inundation, particularly during the
afternoon/evening high tide period. Despite the south swell surf
declining, and the height of the high tides diminishing, impacts
are still expected through Memorial Day, but are not expected to
be as large of an impact as the last couple of days. Please see
the Special Weather Statement (SPSHFO) product for more
information about the potential impacts from the high tides
combined with the large surf.

A similar period of tides exceeding 2 feet are expected in mid to
late June, between June 21 and June 27. It is during this period
that tide levels are expected to reach the same heights as during
this current event.

A northeast swell building today will produce moderate surf
through Memorial Day along east facing shores. North swells will
be very small though Memorial Day. A moderate north northwest
swell is forecast to arrive Monday night, peak below advisory
levels Tuesday night, then subside through Thursday.

Light winds are expected to persist through Memorial Day, with
trade winds forecast to gradually strengthen starting Tuesday.
Winds could reach Small Craft Advisory (SCA) levels in the typical
windier locations around Maui County and the Big Island





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