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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 270134

Area Forecast Discussion
National Weather Service Honolulu HI
334 PM HST Tue Jan 26 2021

A weakening disturbance west of the state may produce a few heavy
showers tonight, while breezy trade winds focus rainfall over
windward slopes. Increasingly stable trade wind weather will
spread over the region on Wednesday. A stable and breezy trade
wind flow will prevail Thursday through the weekend, with a period
of more active showers due on Friday. Trade winds are expected to
weaken and shift out of the southeast as a front approaches early
next week.


The atmosphere is gradually drying out, though a few heavy
showers cannot be ruled out in the breezy trades tonight.
Afternoon soundings show a slight decrease in moisture, and aside
from a lone thunderstorm flaring on the leeward slope of Mauna
Loa, nearly all heavy showers have been located southwest and
west of the islands in an area of convergence associated with a
surface trough. The combination of strong high pressure centered
far north of state and the nearby surface trough is maintaining
breezy and gusty easterly trade winds. A broad upper-level trough
is lingering over the region, but instability created by this
feature is being countered by drier mid-level air moving in from
the east pushing deeper moisture westward. While a few briefly
heavy showers can be expected in the trade wind flow tonight, the
flood risk has diminished, and the Flash Flood Watch has been
cancelled along with the Winter Storm Warning for the high Big
Island Summits.

Increasingly stable trade wind weather will spread over the state
on Wednesday. The surface trough to the west of the state will
continue to weaken. As a result, the GFS and ECMWF models show
the the area of deep moisture convergence near the trough moving
farther west as drier mid-level air fills in from the east. High
clouds may linger, but typical shower activity is expected over
mainly windward areas.

Breezy trade wind weather will prevail Thursday through the
weekend. A mid-level ridge will lead to more stable conditions,
and showers will be focused over typical windward slopes.
The GFS and ECMWF are showing a band of enhanced trade wind
showers moving through Friday.

Trade winds will decrease and possibly shift southeasterly on
Monday as a front approaches. The front may may over the islands
Tuesday or Wednesday.


Breezy trades and prevailing VFR will continue into tonight for
most locations. The exception in the near term is Oahu where cig
improvement since this morning has been modest. While there is
some potential for MVFR to persist into tonight, the expectation
is still that increasingly dry air moving over the area will
eventually favor VFR. Increasing moisture late tonight will bring
increasing windward showers and a greater probability of MVFR,
especially to Windward Big Island and Kauai.

AIRMET Sierra for tempo mountain obscuration is in effect for
Windward Oahu.

AIRMET Tango remains in effect for low-level mechanical turb and
strong surface winds.


A series of highs will help maintain breezy easterly winds through
the rest of the week, then taper back to a more typical, locally
breezy distribution late in the weekend. The strong winds generated
locally and upwind of the islands have resulted in very rough and
elevated seas and high surf along east facing shores. A Small
Craft Advisory (SCA) is in place for all coastal waters through 6
pm HST Wednesday. The High Surf Advisory (HSA) for east facing
shores has been extended through Wednesday night. Trade wind swell
heights will lower somewhat, later in the week, though surf will
remain at or around advisory level.

The current NW swell will continue to trend down through Wednesday.
A set of WNW to NW swells arrives Thursday night with surf peaking
Friday night and Saturday near advisory levels for north and west
facing shores. In the longer range, models indicate a lack of the
strong storms in the North Pacific that recently brought very
large surf to Hawaii. This will support smaller swells ranging
from the NW to NNE directions.

A surface low is forecast to drop south along the Pacific Northwest
then dissipate off the northern California coast Wednesday and
Wednesday night. This low generated a N to NNE swell pulse toward
the islands, which will give a boost to the surf along exposed
north and some east facing shores beginning Thursday. Swell and
surf are expected to peak Friday/Friday night, then gradually
subside through the weekend.

Surf along south facing shores will trend up through midweek, as
an out-of-season swell from the Tasman Sea arrives. Surf should
lower back to winter averages through the second half of the week.


High Surf Advisory until 6 AM HST Thursday for Kauai Windward-
Oahu Koolau-Olomana-Molokai Windward-Maui Windward West-Windward
Haleakala-Big Island North and East.

Small Craft Advisory until 6 PM HST Wednesday 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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