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Hawaiian Islands Synoptic Discussion and Guidance

FXHW60 PHFO 151950

Area Forecast Discussion
National Weather Service Honolulu HI
950 AM HST Mon Apr 15 2024

The wet pattern will continue over the eastern end of the state
today as a cold front continues eastward. Meanwhile, light to
moderate west-northwest winds with drier air will continue to
fill in from west to east in the wake of the front. Building high
pressure builds north of the state will bring a return to a more
typical trade wind pattern, with scattered windward and mauka-
focused showers Wednesday through the second half of the week.


The short-term guidance remains in good agreement with the wet
pattern persisting today over the eastern end of the state, due
to an upper trough to the north and a front slowly advancing down
the island chain. The latest analysis has the front over Maui this
morning moving southeastward. Radar imagery shows the associated
shower band has all but dissipated over the last few hours, with
mainly scattered showers coming up from the southeast ahead of the
front. Behind the front, scattered showers are being carried in
on the west-northwest winds. The latest rainfall summary depicted
24-Hr rainfall totals (through 6 AM HST) ranging from 3 to 5 inches
on Kauai to 1 to 2 inches over Oahu and Maui County. In addition
to the wet conditions, expect a wintry mix over the Big Island
summits through the remainder of the morning. Strong westerly flow
aloft is causing warning-level winds on the Big Island Summits
and advisory-level winds for Haleakala summit. These conditions
are expected to continue through tonight.

Elsewhere, light to moderate west-northwest winds and drier conditions
have begun to fill in from west to east. Dewpoints are forecasted
to dip into the low 60s by this afternoon, which will limit rainfall
chances. On Tuesday, drier conditions will spread to the eastern end
of the state as the front moves east of the area. Winds will shift
out of the north through Tuesday, becoming northeast trades by Wednesday
as high pressure builds to the north of the state. A return to a more
typical trade wind pattern is anticipated for Wednesday through the
second half of the week, with moderate wind speeds and clouds/showers
favoring windward areas.


A weakening front moving over Maui will move east of the islands
over the next 24 hours of so. Skies have cleared over Kauai and
Oahu behind the front, and clearing is expected over Molokai
shortly. Clearing over the remainder of Maui County is expected
later today. Some lingering clouds and showers will trail over the
Big Island.

AIRMET Sierra for mountain obscuration is currently in effect for
Maui and Lanai. Conditions are expected to improve this afternoon.

AIRMET Tango is in effect for mechanical turbulence N through NE
of the mountains on the Big Island.

Occasional light rime icing is expected in layered clouds above 15
kft from Molokai eastward. Conditions will continue today, but
some improvement is expected from west to east as the front moves
away from the islands.


A front over Maui County will continue to move SE through Tuesday,
with the front expected to dissipate SE of the Big Island by
Wednesday. Clouds and showers associated with the weakening frontal
boundary are gradually easing in both coverage and intensity. Light
to moderate W to NW winds will follow the front today, with locally
strong S to SW winds ahead of the front over Big Island waters.
High pressure building NW of the islands will support light to
moderate NW to N winds that will veer to the NE and strengthen
somewhat after midweek.

A Small Craft Advisory (SCA) for the Alenuihaha Channel and
leeward Big Island waters will likely be allowed to expire later
today as S to SW winds diminish, while increased seas in Kauai
waters has led to an extension of the SCA through Tuesday.

Surf along N and W facing shores will build today as a mixed-
period NW swell builds, with resultant surf approaching High Surf
Advisory levels along exposed shores of Kauai and Oahu as the
swell peaks overnight. This swell will gradually diminish as it
becomes increasingly N the next couple of days. Otherwise, small
swells from the SSE and SW will support small surf along S facing
shores the next couple of days. Surf along E facing shores will
remain very small, then gradually trend up as NE trade winds
increase later in the week.


Wind Advisory until 6 AM HST Tuesday for Haleakala Summit.

High Wind Warning until 6 AM HST Tuesday for Big Island Summits.

Winter Weather Advisory until 11 AM HST this morning for Big
Island Summits.

Small Craft Advisory until 6 PM HST Tuesday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters.

Small Craft Advisory until 6 PM HST this evening for Alenuihaha
Channel-Big Island Leeward Waters.



AVIATION...M Ballard

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