Current Conditions
Temp6.0 C
RH29 %
WindS 0 mph
RoadOpen (4x4)
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Hawaiian Islands Synoptic Discussion and Guidance

235
FXHW60 PHFO 241937
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
937 AM HST Sun Mar 24 2019

.SYNOPSIS...
Moderate to locally breezy trade winds will continue through
Monday as a surface high passes north of the islands. Modest
windward rainfall will prevail today, followed by an increase in
showers for most windward areas on Monday. Trade winds will
steadily drop Tuesday, then become variable on Wednesday ahead of
a front. The front will advance through much of the state on
Thursday, bringing northerly winds behind and an increase in
showers.

&&

.DISCUSSION...
A stable, locally breezy trade wind flow remains in place across
the state, while the southern edge of a band of low level moisture
continues to enhance clouds and showers on windward Kauai. The
trades are being driven by a 1031 mb surface high currently
located nearly 900 miles north of Kauai. Little change in winds is
expected over the next 24 hours as the high drifts toward the
southeast. The moisture band will affect windward Kauai through
early afternoon, then lift northward. Otherwise, expect typical
windward rainfall and rather dry leeward conditions through
tonight. The atmosphere will remain stable with a firm low level
inversion. An approaching upper level trough will continue to
produce thin high clouds today, followed by a decrease in high
clouds tonight.

An increase in shower activity is expected Monday. As the surface
high shifts to the northeast of the state, the band of low level
moisture currently impacting Kauai will be pushed over much of
the state. Rainfall will be focused over windward slopes. However,
the upper level trough passing overhead will weaken and lift the
inversion, allowing some showers to periodically spread to leeward
areas on the easterly trade winds.

Easterly trade winds will steadily decline on Tuesday and will be
disrupted on Wednesday as a front approaches. Surface high
pressure will weaken far northeast of the state on Tuesday,
causing trades to fall to gentle to moderate strength. As the
front advances, it will push the surface ridge over the region on
Wednesday, causing winds to weaken significantly. Expect a land
and sea breeze regime to prevail, with afternoon clouds and
showers developing over interior sections. Although low level
moisture will be around seasonal average, an approaching mid to
upper level trough will create some instability. As a result, an
isolated, briefly heavy shower could be possible on Wednesday.

A late season frontal passage is becoming increasingly likely on
Thursday. The front is expected to reach Kauai late Wednesday
night, move down to Maui Thursday afternoon, then possibly reach
the Big Island Thursday night before stalling. The GFS and ECMWF
are still not in agreement on the details, but expect a period of
increased rainfall, especially along windward and north facing
slopes, as the front moves through. Northerly winds should fill in
behind the front, ushering in a rather cool, winter-like air mass
with dew points in the mid 50s for the north half of the island
chain. There is a good chance that the front will stall near the
Big Island, where showers could linger along windward slopes.

&&

.AVIATION...
High pressure centered far north of the Hawaiian Islands will
drive moderate to fresh trade winds through Monday. Scattered high
clouds will pass over the islands today and tonight. Low clouds moving
along the trade wind flow will bring periods of showers with
brief MVFR cloud ceilings over the windward mountain slopes of
each island. AIRMET Sierra is posted for more extensive mountain
obscurations in showers on Kauai this morning as the southern edge
of a moisture band north of the state tracks by. Look for
improving visibility and ceilings on Kauai this afternoon.
Elsewhere, VFR conditions will prevail.

&&

.MARINE...
A slight uptick of trades is expected this afternoon and tonight
as high pressure strengthens north of the state. Fresh to strong
trades are expected to be in place through Monday night. The
trades will ease Tuesday and Tuesday night as a front approaches
from the northwest, with winds becoming light and variable by
Wednesday. The front is expected to make its way down the island
chain from west to east starting Wednesday night and moderate to
fresh north winds will fill in behind the frontal passage. Winds
are expected to return to a more typical trade wind flow by next
weekend as high pressure builds north of the state.

A Small Craft Advisory (SCA) remains in effect for most waters
through 6 PM this evening due to winds, elevated seas or a
combination of the two. As seas decrease tonight, the SCA has been
scaled back to the typically windy waters around Maui and the Big
Island tonight through Monday night.

A small reinforcing north-northwest swell will continue to produce
moderate surf along north facing shores today. This swell will
gradually lower over the next few days. A small reinforcement out
of the north is expected late Monday into Tuesday followed by
another small west-northwest swell Tuesday night. A moderate
long-period west-northwest swell is expected to fill in on
Wednesday and peak Thursday. This swell may approach advisory
levels Thursday through Friday along north and west facing
shores. Another long period northwest swell could arrive next
weekend.

Surf along east facing shores will rise today through Monday due
to a slight increase in trade wind speeds. A downward trend is
expected Monday night through Wednesday as the trades ease.

Surf along south facing shores will remain small most days with
mainly background long period southerly pulses and short-period
southeast energy expected. There could be a bit of a bump
Wednesday through Friday as a small long period south swell
arrives from the southern hemisphere.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 AM HST Tuesday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

Small Craft Advisory until 6 PM HST this evening for Kauai
Northwest Waters-Kauai Windward Waters-Kauai Channel-Oahu
Windward Waters-Kaiwi Channel-Maui County Windward Waters-Big
Island Windward Waters.

&&

$$

DISCUSSION...Wroe
AVIATION...Foster
MARINE...Kino

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