Current Conditions
Temp2.3 C
RH23 %
WindW 3 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 280157

Area Forecast Discussion
National Weather Service Honolulu HI
357 PM HST Sat May 27 2017

Variable winds will allow hot and humid conditions to continue
through Memorial Day. Localized land and sea breezes will prevail
with passing showers, with afternoon convection focusing showers
over interior and leeward areas. Afternoon showers may be heavy
at times as an upper level trough passes over the state today and
Sunday. Typical trade wind weather is expected to return Tuesday
as high pressure strengthens north of the islands.



An area of low pressure NE of the state has 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 has become hot and humid during the day with cooling
temperatures at night. Current afternoon conditions are partly to
mostly cloudy skies over the islands with sea breezes and land
heating creating rising motion over interior areas. Some scattered moderate
showers have formed so far today, and heavier showers are
possible into the evening. A diurnal pattern of clearing skies
overnight with clouds and passing showers during the day will
continue through Memorial Day.

An upper level trough now over the western end of the state will
move eastward over the weekend bringing some instability to the
atmosphere. The afternoon sounding from Lihue shows a respectable
increase in atmospheric instability with ML CAPE increasing from
zero overnight to 500 J/kg this afternoon. This instability has
weakened our normally cloud capping temperature inversion, and
will allow for some locally heavy showers to develop during the
peak afternoon convective times, and last into the evening. The
trough is expected to be over the Big Island by Sunday afternoon
and there will be a chance of thunderstorms over the higher
elevations of Mauna Kea and Mauna Loa along with the potential of
freezing rain at the summits.

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


A light wind regime will remain over the islands through Sunday,
with daytime sea breezes and overnight land breezes expected in
most areas. Showers are expected to focus over the interior of the
islands during the afternoon and early evening hours, and over
the coastal waters overnight. Some MVFR cigs/vsbys in SHRA will
continue to impact the interior of the islands through early this
evening, with localized IFR conditions possible in +SHRA, mainly
across Kauai and Oahu. Can't rule out some brief reductions in
cig/vsby at the terminals, but predominantly VFR conditions should
prevail through the TAF forecast period. The one exception is
PHNY, where MVFR cigs are expected to remain in place through
early this evening.

AIRMET Sierra is in effect for mountain obscuration across Kauai.
The AIRMET may need to be expanded to include some of the other
islands later this afternoon. AIRMET Tango may be needed for
moderate upper level turbulence between FL300 and FL400 late this
afternoon and tonight, as an upper level trough moves over the
island chain.


Surf heights are expected to peak tonight due to a large south-
southwest swell, then gradually diminish into early next week. As
a result, a High Surf Advisory remains in effect through Sunday
afternoon for all south facing shores. Please see the latest
Coastal Hazard Message (CFWHFO) on our website for additional
information about the hazardous surf conditions.

In addition to the elevated surf along south facing shores,
coastal flooding impacts associated with record-level King Tides
will continue through the weekend along all shores, especially in
Maui County and Oahu. Beaches and shorelines, boat ramps and
docks, and vulnerable low-lying roads and structures will be
impacted during these late afternoon and early evening high tides.
Please see the Special Weather Statement (SPSHFO) product on our
website for more information about the potential impacts from the
high tides combined with the large surf.

Elsewhere, surf along east facing shores will trend down through
the weekend due to the light winds. However, a small short-
period north-northeast swell will support small surf through
Monday along east facing beaches and reefs with exposure to swell
energy from this direction.

Small background surf is expected to persist along north facing
shores, mainly at locations exposed to the north-northeast swell
mentioned above. The latest wave model guidance continues to show
a small to moderate north-northwest (330-340 deg) swell filling in Monday
night through mid-week due to the fetch associated with the
circulation around a surface low tracking north of the state later
this weekend.

Winds will remain light into early next with no Small Craft
Advisory (SCA) anticipated during the Memorial Day weekend. The
latest forecast indicates the trades may strengthen again around
mid-week, so a SCA may be needed for the typically windy waters
adjacent to the islands of Maui County and the Big Island starting


High Surf Advisory until 6 PM HST Sunday for Niihau-Kauai
Windward-Kauai Leeward-Oahu South Shore-Waianae Coast-Molokai
Leeward-Lanai Makai-Kahoolawe-Maui Leeward West-Windward
Haleakala-Leeward Haleakala-Kona-South Big Island-Big Island
North and East.




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