Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 180154
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
354 PM HST Sun Mar 17 2024

.SYNOPSIS...
Other than a brief increase tonight, moderate trade winds will
continue through the first half of the week. Mostly dry and stable
conditions are anticipated as well, though the best chance for
light showers will be over windward and mauka areas. A return of
breezy easterly trades and increasing rainfall chances is possible
during the second half of the week as an upper disturbance moves
into the area.

&&

.DISCUSSION...
Afternoon 00z soundings from Lihue and Hilo show that drier and
more stable conditions are settling over the region. Precipitable
water values are now below 1 inch at both locations, and there are
strong inversions near 5,000 feet. Satellite imagery shows that
clouds are favoring typical windward and mauka areas, though
onshore flow across sheltered leeward areas this afternoon has
contributed to increased cloud cover there as well. Showers,
however, are very limited with rain gauge networks showing that
the state has remained largely dry this afternoon.

Mostly dry and stable conditions will remain 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
moderate easterly trade winds for the next several days, though
the latest guidance does suggest a brief increase in winds
tonight. Minor adjustments have been made to the forecast with
this afternoon`s updates to trend towards the latest guidance, but
the overall forecast philosophy remains unchanged. The best
chances for a few showers through mid-week will be over typical
windward and mauka locations, especially during the overnight
through the early morning hours each day. 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 -15C 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. As such, clouds and showers will favor windward and mauka
areas, especially overnight into the morning hours. Brief periods
of MVFR conditions will be possible in any heavier showers that
manage to develop, but with atmospheric stability in place under a
ridge and a only a shallow layer of low level moisture available,
shower coverage and intensity should be limited. VFR conditions
are expected to prevail across the state through the forecast
period.

No AIRMETs are in effect and none are anticipated to be needed
through Monday.

&&

.MARINE...
A brief increase in northeast to east trade winds is expected
tonight as a building surface high passes about 350 nm north of
the state and a trough deepens far east of Hawaii. A Small Craft
Advisory (SCA) has been issued for the expected increase in
winds. Trades will ease back to moderate to locally fresh levels
on Monday as high`s trailing ridge settles about 200 to 300 nm
north of the state. Little change is expected through Wednesday,
when another high will develop farther to the north of the
islands. As the new high builds on Thursday and Friday, trades
will increase to fresh to locally strong levels, and a SCA will
be needed for at least the typically windy waters around the Big
Island and Maui. The stronger trades look to hold into next
weekend.

Several overlapping northwest swells are due this week, and the
latest moderate northwest (310-320 degree) swell has been on a
slow rise today. At NOAA buoys 51001 and 51101 the swell has been
hovering mainly in the 7 to 8 foot range at 16 to 17 seconds
since sunrise. Given the travel time to the islands, expect a
continued rise through the evening and a peak in surf along most
north and west facing shores from Kauai to Maui near the High
Surf Advisory (HSA) level overnight. We will continue to monitor
the buoys but have decided to hold off on the issuance of an
advisory for now. This swell will decline late Monday and Tuesday,
followed by a larger northwest (310-320 degree) swell building
Tuesday night. Altimeter data from last night 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.

An inconsistent pulse of early season, south-southwest swell has
been 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...
Small Craft Advisory until 6 AM HST Monday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.


&&

$$

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


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