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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 222004

Area Forecast Discussion
National Weather Service Honolulu HI
1004 AM HST Sat Jan 22 2022

Breezy trades will bring an increase in windward and mauka showers
tonight. Much drier weather is then expected by Sunday afternoon
as trades become locally strong. Trades will then gradually weaken
from Monday onward. During this time, light showers will mainly
focus over windward and mauka zones.



Visible imagery shows mostly clear skies from the Big Island through
Molokai this morning with mostly cloudy skies and scattered showers
over windward Kauai extending eastward into the Kauai Channel. These
showers are associated with a dissipating SW-NE oriented frontal
boundary that extends well northeast of the state. During the next
24 hours, the upstream portion of the remnant frontal zone will
become increasingly entrained in the locally breezy trades causing a
brief increase in windward shower coverage tonight into early Sunday
before shifting west of the area. By Sunday afternoon, a building
mid-level ridge and healthy dry advection will support a quick
transition to a dry trades type of pattern. Forecast soundings
indicate a rapid increase in stability as inversion heights fall to
around 4kft by Sunday evening. As such, clouds should be at a
minimum by Sunday afternoon with very little in the way of showers
despite building trades. Through at least early Tuesday, trades will
largely be modulated by a shallow low pressure passing southeast of
the Big Island. Thus, despite the large scale pattern being more
supportive of moderate trades, the next 60 hours or so will be
better characterized as breezy with a period of locally strong
trades possible Sunday into Sunday night as inversion heights come
down. An upper trough will deepen east of the area on Sunday
bringing no detectable change in sensible weather at or near sea
level locations. However, as the mid-level jet anchored along its
western periphery strengthens, winds could approach wind advisory
criteria for the the Big Island Summits late Sunday into early
Monday. Light or moderate trades then dominate mid to late week.



A band of clouds and showers which formed along the edge of a
decaying frontal boundary, drifted over the western portions of
the state overnight. Expect that this band of moisture will remain
mainly centered across portions Kauai into this evening as
easterly trades strengthen across the region. Otherwise, the
latest radar trends show isolated to scattered showers developing
along and between islands in low level convergent flow.

A surface ridge remains anchored over the islands which will
reinforce more dominate easterly trades this weekend. Overall
expect limited chances for showers through the TAF period, with
persistent trades focusing the best chance for showers and cloud
cover along favored windward slopes. Mainly VFR conditions
continue, however a brief period of MVFR cigs is possible in
developing trade wind showers.

AIRMET Sierra remains in effect for Tempo Mountain Obscuration
above 020. Low cloud ceilings will remain possible across Kauai
with lessening influences over Oahu.

Additionally, monitoring a potential need for AIRMET Tango
for a period of moderate turbulence as trades strengthen and
blow across mountain terrain.



Trades have filled in statewide and will reach the fresh to strong
category for exposed waters by Sunday. These winds combined with
large seas associated with an incoming very large west-northwest
swell have led to Small Craft Advisory conditions for all Hawaiian
waters. Trades may shift to a more northeast direction early next
week as the islands become positioned between low pressure
passing to the southeast and the ridge to the north.

Surf along exposed north and west facing shores is on the rise as
the new swell builds down the island chain. Exposed nearshore
PacIOOS buoys have ramped up quickly to several feet above
predicted levels early this morning, which supports surf heights
climbing well above warning levels (largest Kauai). Expect this to
hold through most of the day with the offshore buoys still
registering a swell height around 20 ft. A gradual downward trend
is then expected tonight through the second half of the weekend as
the swell begins to ease. Surf heights should dip below warning
levels Sunday.

Although a downward trend is expected through the second half of
the weekend, another long-period, west-northwest pulse arriving
early Monday morning will support advisory-level surf persisting
through the day Monday. Heights should then dip below advisory
levels for north and west facing shores Tuesday through the second
half of next week.

Surf along east facing shores may trend up late tonight and early
Sunday morning in response to a tight gradient that has setup
between low pressure centered near 750 miles east of Hilo and
high pressure to its north. Recent ASCAT data showed a packet of
strong to gale-force winds focused at the state north of the low
within the 060 to 080 degree directional bands relative to the


High Surf Warning until 6 AM HST Sunday for Niihau-Kauai Leeward-
Waianae Coast-Oahu North Shore-Maui Windward West-Kona-Kohala-
Kauai North-Molokai Windward-Molokai North-Molokai West-Maui
Central Valley North-Windward Haleakala.

Small Craft Advisory until 6 AM HST Sunday for all Hawaiian




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

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