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Temp2.5 C
RH7 %
WindNE 17 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

192
FXHW60 PHFO 240201
AFDHFO

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

.SYNOPSIS...
Strong trades will bring a wet windward and mauka shower weather pattern
through Wednesday. 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 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 the afternoon showers.

&&

.DISCUSSION...
Breezy trade winds across Hawaii are driven by a strong high
pressure system far north of the area. The trades are carrying in
scattered showers focused over the windward slopes of Maui County
and the Big Island this afternoon, and occasionally passing to
leeward sides due to the momentum from the trades. A stalled and
weakened front is located about 50 miles north of Kauai indicated
on visible satellite as a 75 mile wide band of broken cumulus clouds.

Showers will fill back in over the western part of the state
tonight and Wednesday as the clouds and showers over Maui County
and the Big Island track westward. Clouds and showers will
continue to filter in with the trades, so some showers continue
across windward Maui and Big Island through Wednesday.

The trades will begin to weaken around Wednesday night through the
end of the work week. The background flow will remain easterly and
will likely tap into the lingering moisture over the state and
bring continued windward showers during the second half of the
week. Leeward areas will see overall less showers during the
nighttime, but we may see a hybrid sea breeze pattern that may
produce some afternoon cloud build ups and showers by Friday.

Winds will continue to weaken to a pure nighttime land breeze and
daytime sea breeze pattern through the weekend due to a weak
trough setting up west of the state. The trough will induce
southeast background flow that will bring warm humid and voggy
conditions through the Memorial Day weekend. Aloft, a weak upper
level trough will swing west to east over the islands and may
enhance the afternoon sea breeze driven showers.


&&

.AVIATION...
A strong high pressure center north of Hawaii will keep the
islands in a moderate strength northeasterly trade wind
regime through Wednesday. The wind speeds are strong enough to
generate mountain wave turbulence in the low levels below 8000
feet over and immediately south through west of all islands.
A trough moving through the islands will bring scattered to
numerous showers over Maui Molokai and Oahu after 23Z. Overall
instability in the trade wind flow will continue to produce
scattered shower activity with periods of MVFR ceilings and
showers for the next few days.

AIRMET Sierra in effect for mountain obscuration across Maui
Molokai and Lanai.

AIRMET Tango remains in effect for low level turbulence over and
downwind of the terrain of all islands due to moderate
northeasterly trade winds.


&&

.MARINE...
Breezy and locally strong trade winds will continue tonight due to
high pressure to the north of the islands. Winds are expected to
begin to trend down late tonight and tomorrow. The Small Craft
Advisory (SCA) remains in the effect for most waters through
tonight, but as the winds decrease, expect the SCA to be scaled
back first the typical windier areas near Maui and the Big Island
tomorrow, before being dropped.

The current northwest swell will veer to the north northwest
tonight and Wednesday and it continues to decline. A series of
small, short period north northeast swell are expected later this
week and into the weekend. Surf along north and west facing
shores is expected to remain below advisory levels. The short
period swell generated by the trade winds will continue to bring
choppy surf to east facing shores, but should be on the decline as
the winds decrease.

The current small south swell will linger through Wednesday. A
larger south swell is expected to arrive Friday and continue
through most of the Memorial Day weekend. This swell is expected
to produce advisory level surf along south facing shores. This
south swell will coincide with high astronomical tides associated
with the new moon. This combination will likely result in minor
coastal flooding due to wave run-up along south facing shores,
especially near the high tide times from Wednesday afternoon
through Sunday night.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
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.


&&

$$

DISCUSSION...Foster
AVIATION...Bohlin
MARINE...M Ballard

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