Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 171919
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
919 AM HST Sun Mar 17 2024

.SYNOPSIS...
Moderate northeast trades will shift out of the east later today
through Monday, then continue through the first half of the week.
Despite a few windward and mauka clouds and showers, a gradual
trend towards mostly dry and stable conditions is anticipated
through the first half of the week. A return of breezy easterly
trades and increasing rainfall chances is possible through the
second half of the week as an upper disturbance moves into the
area.

&&

.DISCUSSION...
Latest satellite imagery this morning shows that clouds and a few
light showers embedded within northeasterly trade wind flow are
favoring typical windward and mauka sections of the islands. At
the surface, the remnants of an old front (now a trough) are
located east of the state and will continue moving east away from
the islands. Meanwhile, a ridge axis stretches north of the state.
CIMSS MIMIC layer precipitable water shows that what was left of
any lingering moisture across the eastern end of the island chain
associated with the old boundary is now diminishing. Therefore,
expect some lingering clouds and showers over windward and mauka
sections of the islands today, but they should become less common
this afternoon into Monday as drier air with precipitable water
values less than 1 inch overspreads the islands from the north.

Guidance remains in good agreement that dry and stable conditions
will settle over the state during the first half of the week as
ridging aloft moves over the region. High pressure building north
of the state will result in trade winds shifting to become more
easterly and maintain moderate levels. The best chances for a few
showers will be over typical windward and mauka locations
overnight through the early mornings. Any leeward showers are more
likely to occur in the afternoons, where localized sea breezes
form.

A gradual strengthening and destabilization of the trade wind
flow is possible Wednesday into Friday. Trade wind speeds will
increase as a deeper surface high sets up far north of the state,
reaching breezy levels by Friday. Meanwhile, an upper-level
trough will slowly pass over the region, bringing 500 mb
temperatures as low as -16C on Wednesday night and Thursday.
While there could be some increase in shower coverage in response
to the added instability, mid-level ridging may limit the overall
rainfall potential.

&&

.AVIATION...
Moderate east-northeast trades will persist through early this
week, bringing shallow isolated to scattered showers to windward
coasts and slopes. Some low level moisture is lingering across the
eastern end of the state this morning, bringing periodic MVFR
ceilings and visibility in low clouds and showers. See AIRMET
Sierra below. These conditions will gradually improve today, and
VFR will prevail across the state through the forecast period.

AIRMET Sierra remains in effect for mountain obscuration along
northeast facing slopes of the Big Island this morning. These
conditions are expected to gradually improve by this afternoon.

&&

.MARINE...
Moderate to locally fresh northeast to east trade winds will
persist through Wednesday as weak high pressure drifting about
200 to 300 nm north of the state is eventually replaced by
another high farther to the north. As the new high builds on
Thursday and Friday, trades will increase to fresh to locally
strong levels, and a Small Craft Advisory will be needed for at
least the typically windy waters around the Big Island and Maui.

Several overlapping northwest swells are due this week. As a
small north-northwest swell fades today, a moderate northwest
(310-320 degree) swell is building in. The PacIOOS Waimea Bay buoy
has been showing an increase in long period energy for the past
few hours, and the swell will peak tonight near High Surf Advisory
(HSA) levels for most north and west shores from Kauai to Maui.
We will closely monitor NOAA buoys 51001 and 51101 to determine if
a short-lived advisory will be needed for tonight and early
Monday. This swell will decline late Monday and Tuesday, followed
by a larger northwest (310-320 degree) swell building Tuesday
night. Overnight altimeter data showed the seas within the fetch
aimed at Hawaii are slightly larger than model guidance. As a
result, this swell will lead to surf well in excess of HSA levels
for most north and west facing shores Wednesday into early
Thursday. This swell will decline later Thursday and Friday, with
a moderate northwest swell due next weekend.

A pulse of early season, south-southwest swell is building today.
Expect the swell to peak slightly above March average tonight and
Monday, then gradually decline through Wednesday. Short period
trade wind swell will be below seasonal average through Thursday
and will likely pick up Friday and next weekend as trade winds
increase.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Vaughan
AVIATION...Farris
MARINE...Wroe


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