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Temp-1.9 C
RH57 %
WindSW 19 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 270711 CCA

Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
830 PM HST Fri May 26 2017

Light winds with localized land and sea breezes will prevail across
the island chain as pressure gradient slackens across the region
through the Memorial Day weekend. Passing showers will favor
windward areas, while convection developing in the afternoons and
evenings over the islands will bring showers to the interior and
leeward sections. Typical trade wind weather is expected to return
early part of next week as high pressure is expected to strengthen
just north to northeast of the islands.


Mainly fair weather prevails over much of the islands this evening,
as not much low clouds are present in the island vicinity. The
exceptions are Kauai, where persistent low clouds continue to bring
some showers to that island and vicinity, and Maui and the Big
Island, where lingering clouds from afternoon convection will
continue through early part of the evening, providing some showers.
Rather light winds present across the island chain this evening,
with land breezes developing, as pressure gradient slackens across
the region.

A weak pressure pattern will prevail in the island vicinity through
the Memorial weekend as high pressure far northwest continues to
weaken far northwest. Therefore, synoptic winds will stay light
across the island chain through the Holiday weekend, with a general
background easterly flow. Widespread daytime sea breezes and
overnight land breezes are expected. Clouds will build over the
interior and leeward areas of the islands during the day under the
converging sea breezes, with showers developing, while there will be
some clearing at night as diverging land breezes develop. The
background light easterly wind flow may also bring some clouds and
showers to the windward areas at times. An upper level trough
currently northwest of the islands will pass over the area in the
next couple of days. It will bring cold temperatures aloft,
allowing the airmass in the island vicinity to become more unstable.
Showers will be enhanced, with locally heavy downpour possible. As
the upper level trough sweeps in from the northwest, Kauai and Oahu
may see more active weather on Saturday. And as the trough travels
east, the focus will turn to the eastern islands late Saturday into
Sunday. Atmospheric conditions may become unstable enough for even a
thunderstorms to develop over the Big Island. Shall consult with the
latest model runs before adding the mention of thunderstorm chance
to the forecast package at this point.

High pressure far northeast of the state is expected to extend
westward early part of next week, and may stay north to
north-northeast of the islands through later part of the next week.
This will bring stronger trade winds back to the island chain by
late Tuesday, with speeds reaching moderate levels later part of
next week. Airmass in the island vicinity is expected to become more
stable as an upper level ridge builds in the region. Thus, typical
trade wind weather is expected for the islands for much of next week
at this point.


Light winds will allow island-scale land and sea breezes to drive
weather conditions over the islands and adjacent waters through
Saturday. The expectation is for general clearing and prevailing VFR
over most land areas through early Saturday as land breezes clear
skies. ISOL MVFR in SHRA are possible, mainly over Kauai and
adjacent waters, due to the presence of increased moisture
associated with a nearby stalled frontal boundary. Sea breezes
converging over the islands Saturday afternoon will lead to the
development of clouds and showers over island interiors. A
developing trough aloft will destabilize the island atmosphere,
allowing for the development of +SHRA that are expected to bring
TEMPO MVFR and ISOL IFR CIG/VIS, mainly between 22Z and 04Z.

No AIRMETs are in effect, but localized mountain obscuration may
prompt the issuance of AIRMET SIERRA Saturday afternoon. VFR
conditions are expected to prevail at the TAF sites, except for MVFR
CIG at PHNY from 20Z-04Z, and the chance of brief MVFR conditions at


Trade winds will continue to weaken during the Memorial Day Holiday
weekend as the pressure gradient across the region continues to
relax in response to a surface low far north-northeast of the state.
These weaker background winds will also allow the locally generated
wind waves to trend down. Therefore, we do not anticipate a need for
a Small Craft Advisory (SCA) into early next week. 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 next

Surf along south facing shores is steadily rising this evening as
the south-southwest swell continues to build. The surf is expected
to peak on Saturday, then slowly subside 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 building surf along south facing shores, coastal
flooding impacts associated with record-level King Tides will
continue each day this 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 and the
south swell.

A small, long-period south swell (170-190 deg) is expected to arrive
late next week. Otherwise, no significant sources of south swell
energy are expected from mid-week through next weekend. Surf along
east facing shores will trend down through the weekend as the trades
relax. However, a small short-period north-northeast swell will
support small surf along east facing beaches and reefs with exposure
to swell energy from this direction through Monday.

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


High Surf Advisory until 6 AM 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