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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 232003

Area Forecast Discussion
National Weather Service Honolulu HI
1003 AM HST Tue May 23 2017

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.


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 this morning,
and occasionally passing to leeward sides of the smaller islands
due to the momentum from the trades.

A stalled and weakening front is located about 60 miles north of
Kauai indicated on visible satellite as a 75 mile wide band of
broken cumulus clouds.

This afternoon looks like Kauai and Oahu will brief respite from
the rain this afternoon, while another batch of clouds and showers
will carry in with the trades over Maui and the windward coast of
the Big Island. By tonight into Wednesday, showers will fill back
in over the western and central part of the state as the frontal
moisture lingers in and combined with the upstream trade wind
showers. In all, we anticipate a wet trade wind pattern likely
over the next 48 hours.

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.


A strong high pressure center north of Hawaii will keep the
islands in a moderate strength northeasterly trade wind
regime through the week. 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 tropical disturbance just east of the islands will bring another
round of scattered to numerous showers over Maui Molokai and Oahu
after 23Z. Overall instability in the trade wind flow will
continue to produce isolated to scattered shower activity with
periods of MVFR ceilings and showers for the next few days.

AIRMET Sierra in effect for mountain obscuration across Kauai.
Expansion of AIRMET Sierra will likely be needed after 23Z for
Maui Molokai and Oahu.

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


High pressure to the north of the islands will maintain breezy and
locally strong trade winds today. Expecting the winds to begin to
trend down tomorrow, and then continue to decrease through the end
of the week. A 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, before being dropped.

The current northwest swell should gradually decline today, and
will veer to the north northwest tonight and Wednesday. A series
of small and short-period NNE swells are expected later this week
into the weekend. East facing shores will see short-period swell
and choppy surf during the next couple of days due to the breezy
trade winds.

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 may produce
advisory level surf of 8 feet or greater 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.


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.



MARINE...M Ballard

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It was last modified on: Wed, Dec 17 2014 - 1841 UTC
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