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RH14 %
WindNE 12 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 240642

Area Forecast Discussion
National Weather Service Honolulu HI
842 PM HST Tue May 23 2017

Strong trades will persist through Wednesday, pushing clouds and
showers across windward areas. Winds will gradually weaken through
the second half of the week, becoming light and variable through
the Memorial Day weekend. Daytime sea breezes and nighttime land
breezes will take over this weekend and bring warm and humid
weather with possible vog. A weak upper trough will pass over the
state this weekend and may provide some enhancement to afternoon


Strong high pressure persists to our north, keeping trade winds
locally strong across the area this evening. Satellite loop shows
showery low clouds embedded within this trade flow moving across
Oahu and the islands of Maui county, keeping windward and mauka
areas of these islands wet and most areas of these islands
cloudy. Overcast low clouds persist across most of the Big Island,
but with less shower activity noted there on radar. Kauai is
clearer and drier this evening than her neighbors. The southern
edge of a 60 mile wide frontal cloud band is about 80 miles north
of Kauai and has not moved much over the past 12 hours or so. The
area of clouds and showers across Oahu and Maui county may spread
to Kauai overnight before moving west of the state.

Models show the trades will begin to weaken Wednesday night
through the end of the work week, then become quite light during
the holiday weekend. Background easterly flow will continue to
tap into lingering moisture over the state and fuel mainly
windward showers during the second half of the work week. Leeward
areas will see fewer showers during the night, but a hybrid sea
breeze pattern may produce afternoon cloud build ups and showers
by Friday. This weekend, background flow will likely veer to
southeasterlies, bringing voggy conditions to the smaller islands
through Memorial Day. Aloft, a weak upper level trough will swing
west to east over the islands and may enhance the afternoon sea
breeze driven showers.


A strong surface high centered far north-northeast of Hawaii will
maintain the breezy low-level trade wind flow across the islands
through Wednesday. A patch of broken to overcast low clouds with
embedded scattered to numerous showers will continue to move
slowly westward over the central islands this evening. This patch
of low clouds and showers is expected to reach Kauai later
tonight. Expect additional low clouds and scattered trade showers
to persist into Wednesday, with periods of MVFR ceilings and
visibilities mainly over the higher terrain and along windward
facing slopes of most islands.

AIRMET Sierra remains in effect for mountain obscuration across
Maui, Molokai, Lanai and Oahu. This AIRMET may need to be expanded
to include Kauai later tonight.

The trade wind speeds are strong enough to generate turbulence
leeward of the mountains on all islands. Therefore, AIRMET Tango
remains in effect for low level turbulence over and below 8
thousand feet downwind of the higher terrain.


The latest surface analysis showed a large area of high pressure
(1041 mb) encompassing much of the northern Pacific that was
centered around 1500 nm north of the waters. Remnants of a lingering
frontal boundary were analyzed from east to west just north of the
Kauai and Oahu waters. The pressure gradient between this boundary
and strong high pressure to its north continues to support a large
area of fresh to strong east-northeast winds. Although the highest
seas associated with these winds are aiming at an area northwest of
the local waters (offshore NDBC buoys 51000 and 51101 peaked in the
9-12 ft range today), seas across the windward waters have been
coming in at the exposed nearshore PacIOOS/CDIP buoys within 7 to 9
ft range (highest Kauai/Oahu waters). The current marine forecast is
lining up well with these observations and no updates are
anticipated in the evening package.

The latest model guidance has initialized well with the current
synoptic pattern discussed and depicts the strong winds locally and
north of the area holding through Wednesday, then trending down
through the second half of the week as high pressure shifts
northeast over the Gulf of Alaska and weakens. Land/sea breeze
conditions will become a possibility over the upcoming weekend,
which will allow the seas to trend down locally.

Surf along east facing shores will remain rough into Wednesday due
to strong onshore winds locally, then trend down through the second
half of the week as the trades relax.

Surf along north facing shores will steadily trend down through
midweek as the northwest swell that peaked on Monday eases and
shifts more out of the north. For the long range, models are hinting
at another moderate north-northwest (340 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

Surf along south facing shores is expected to trend down into
midweek as the small south swell eases. The largest south swell this
season is forecast to fill in late Thursday into Friday, peak Friday
night through Saturday, then slowly ease into early next week. This
swell is currently impacting the Samoa buoy, where wave heights are
coming in slightly higher than predicted by guidance earlier today
(around one ft). A high surf advisory for south facing shores will
be likely through this time, which will continue into the Memorial
Day weekend.

In addition to the expected advisory-level surf through the Memorial
Day weekend along south facing shores, minor coastal flooding is
anticipated due to a combination of record level spring (king) tides
(especially for Maui County and Oahu) and large surf. Similar to the
April 28th through May 1st weekend, when the highest tides on record
were reported for Honolulu, impacts will include beach flooding and
potentially standing water on roadways and low-lying areas near the
coast around the times of high tides each day through the weekend
(see listing of high tide times for Honolulu below).

High Tide times for Honolulu:

5/24 Wednesday 3:36 PM HST
5/25 Thursday 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
Monday afternoon (


Small Craft Advisory until 6 AM HST Thursday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

Small Craft Advisory until 6 AM HST Wednesday for Kauai
Northwest Waters-Kauai Leeward Waters-Kauai Channel-Oahu
Windward Waters-Oahu Leeward Waters-Kaiwi Channel.




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