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fxhw60 phfo 252009 
afdhfo

Area forecast discussion
National Weather Service Honolulu HI
1009 am HST Thu may 25 2017

Synopsis...
lingering clouds and showers will primarily impact Kauai today,
and to a lesser extent Oahu. Trade winds are gradually weakening,
but will still bring a few clouds and showers to the windward
areas of the remaining islands. Winds are expected to be light and
variable over the Holiday weekend, resulting in muggy conditions,
and allow for local afternoon sea breezes, and nighttime land
breezes. An upper level feature could help enhance afternoon
showers over the islands.

&&

Discussion...
a linger area of clouds and showers mostly passed over Kauai over
the last several hours, but there are lingering clouds and showers
over Kauai and a few over Oahu. Elsewhere the clouds and showers
are focused over the windward sides of the mountains in the trade
wind flow. The high pressure system to the far northwest of the
islands is expect to sink southward and weaken through the
weekend. This will continue the downward trend in the winds, with
light and variable winds expected over the weekend.

Dewpoints are expected to edge into the upper 60s this weekend,
and close to 70 Monday and Tuesday. Combined with the light winds,
this will bring muggy conditions to the region.

A weak mid to upper level trough over the area is helping to bring
some unstable conditions to the islands. A deeper upper level
trough is expected to move in from the northwest Saturday and
Sunday. The models agree with colder upper level temperature
moving in, and generally agree with the coldest temperatures
staying to the northeast of the islands. There will be sufficient
moisture, but no organized bands of moisture are expected. The
light winds will allow for clouds and showers to form over the
interior of the islands during the afternoon hours, and the
increase in instability could lead to some enhanced showers.

The background flow will likely be out of the southeast, which
will bring vog up over some of the smaller islands during the
first half of the new week.

&&

Aviation...
high pressure far northwest of the Hawaiian islands will persist.
A moist trade wind flow will continue across the islands through
twentyfour hours and beyond. Clouds and scattered showers will
favor windward slopes and coasts. Isolated spillover showers
possible along leeward sections of the smaller islands, especially
overnight. Some convective development expected across leeward Big
Island in the afternoon and evening hours but the strong inversion
at 9000 ft will limit shower intensity.

Airmet Sierra has been cancelled for all islands except Kauai.
Ceilings may lift briefly this afternoon but will likely lower
again after sunset.

Airmet Tango for mechanical turbulence vicinity of Kauai has been
cancelled as conditions are no longer likely.

&&

Marine...
the latest surface analysis showed a large area of high pressure
(1038 mb) encompassing much of the northern Pacific that
continues to support fresh trade winds across the local waters. An
ascat pass overnight reflected moderate to fresh trades over the
area. Trades are forecast to weaken into the upcoming Holiday
weekend as a weakness within the ridge develops in response to a low
pressure system well northeast of the state, which will allow the
local wind waves to taper off. A small north-northeast swell,
however, will support small surf continuing at the exposed spots
each day into the weekend.

Surf along north facing shores will steadily trend down into the
weekend with mainly surf continuing at spots exposed to north-
northeast energy. For the long range, models are hinting at another
small to moderate north-northwest (330 deg) swell filling in early
next week due to a low tracking east of the date line over the
weekend and deepening as it passes well north of the state on
Monday.

The largest south swell this season is forecast to fill in tonight
and Friday, peak Friday night through Saturday with surf above
advisory levels, then slowly ease into early next week. A few of
the highest energy forerunners may reach the south facing shores
as early as this afternoon. This swell peaked at the Samoa buoy
early Tuesday, which should correspond to a peak locally along
south facing shores Friday night into Saturday. A high surf
advisory for south facing shores will likely be issued this
afternoon, which will continue through the Memorial Day weekend.

In addition to the expected advisory-level surf through the Memorial
Day weekend along south facing shores, impacts from coastal flooding
that have already begun each afternoon with the high tide cycles
will likely become enhanced Friday and Saturday evenings due to a
combination of record level Spring (king) tides (especially for
Maui County and oahu) and large surf expected. These waters levels
could break the late April record that occurred last month at
Honolulu on Friday and Saturday. Flooded beaches, vulnerable low-
lying roads, boat ramps and docks will be impacted during these
hours surrounding the high tides each day. Water levels are
forecast to trend back down toward normal through the upcoming
week.

The following are the daily high tide times for Honolulu that
will correspond to coastal flooding impacts each day through the
weekend:

5/25 today 4:20 PM HST

5/26 Friday 5:07 PM HST (peak water levels/surf expected)

5/27 Saturday 5:55 PM HST (peak water levels/surf expected)

5/28 Sunday 6:46 PM HST

5/29 Monday 7:40 PM HST

For more detailed information on surf for Oahu, see the latest
collaborative nearshore swell and wind forecast that was issued
Wednesday afternoon
(www.Prh.NOAA.Gov/hnl/pages/srf.Php#discussion).

&&

Hfo watches/warnings/advisories...
none.

&&

$$

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