Area Forecast Discussion
Issued by NWS Honolulu, HI

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FXHW60 PHFO 260215
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
415 PM HST Mon Mar 25 2024

.SYNOPSIS...
Breezy east-southeast trade winds will gradually ease into Tuesday.
Modest rainfall will favor typical windward slopes, though leeward
areas may experience an isolated shower. A wetter and breezy trade
wind pattern will return Wednesday into the weekend, before another
brief easing of wind speeds heading into early next week.

&&

.DISCUSSION...
Trade winds have eased and shifted more out of the east-southeast
through the day today, as the weakening high far northeast of the
state continues to move off to the east. This hybrid trade/SE flow
pattern and decreased wind speeds have allowed localized sea breezes
to develop over some wind-sheltered leeward areas this afternoon,
resulting in some clouds over leeward terrain, but little, if any,
rainfall. The scant rainfall is due to a mid- to low-level ridge
producing stable conditions over the state. The afternoon soundings
from Hilo and Lihue still show relatively strong temperature inversions
between 5-6 kft. The soundings also show increasing PW values, mostly
due to increasing moisture in the mid to upper levels from a low
aloft several hundred miles southeast of the state. The increased
moisture is manifesting as stable stratocumulus and upper level
cirrus clouds streaming over the islands from the south. Despite
additional PW, mid-level stability has kept the majority of the
state dry today, with only a few hundredths of an inch along select
windward areas. This mostly dry and stable trend looks to continue
through Tuesday, with some leeward clouds and a spotty light shower
possible again with tomorrow afternoon`s sea breezes before the
trades return later in the evening.

A return to breezy and gusty trade winds is forecast for Wednesday
into at least Friday, as another strong surface high moves north of
the state from the west. The forecast shows upper-level temps cooling
again due to a passing shortwave trough enhancing instability over
the state. This, along with lingering moisture in the mid to low
levels could provide a wetter pattern tradewind pattern through Friday.
In addition, the GFS and ECMWF show a band of moisture from a remnant
boundary embedded in the tradewinds. This would further boost windward
rainfall Friday or Saturday but the models continue to vary on the
timing of this feature. Another brief respite from the breezy trades
is possible heading into early next week as the surface high to the
north once again weakens and moves off to the east.

&&

.AVIATION...
High pressure to the northeast of the state is expected to move to
the east over the next day or two, weakening the moderate trade
winds in place this morning. Clouds and showers will continue to
be carried in on the trade wind flow, and could at times produce
MVFR conditions. High clouds are streaming from south to north
over the islands east of Kauai, but have been thinning since the
morning hours. Expect more thinning overnight as the area of
high clouds continues to drift to the east as an upper level low
south of the islands moves east and opens into an upper level
trough.

AIRMET TANGO was cancelled around midday as low level winds had
weakened. Winds are expected to increase again Tuesday afternoon,
which will likely require another AIRMET TANGO for moderate low-
level mechanical turbulence over and downslope of the mountains.

&&

.MARINE...
Easterly trade winds will continue a brief decline through
tonight, as a 1032 mb surface high centered about 900 nm
northeast of the islands weakens and drifts eastward. Based on
this trend, the Small Craft Advisory (SCA) has been cancelled for
all waters, though winds and seas will be at borderline advisory
levels over windward waters and the typical areas around the Big
Island and Maui through the evening. Trade winds will restrengthen
to SCA speeds over some waters late Tuesday as another high
builds far north of the state, and trades will increase to strong
to near gale strength Wednesday and Thursday, when the SCA will
likely be expanded to all waters. Trade winds will gradually
decline Friday into the weekend, but SCA conditions over the
typically windy waters around the Big Island and Maui are likely.

A west-northwest (300-315 degrees) swell peaked earlier today and
will gradually decline over the next couple of days. Combined
seas at the NOAA buoys northwest of the islands remain rather
high, about 8 to 9 ft, but these observations reflect a mix of
the declining swell and east-southeast wind waves generated from
the recent strong winds over and north of Hawaii. For a better
look locally, the PacIOOS buoy off Waimea Bay is down to 5 to 6
feet at 14 to 15 seconds, which translates to surf just below
advisory levels. Thus, the High Surf Advisory (HSA) for north and
west shores from Kauai to Maui has been cancelled. However, given
the added travel time of the swell to west shores the Big Island,
the HSA will remain in effect there through tonight. Additonal
pulses of small northwest swell are expected Thursday and
Saturday.

Rough east shore surf has fallen to around seasonal average
this afternoon, based on PacIOOS Mokapu buoy readings of about 6
to 7 ft at 9 seconds. East shore surf will lower tonight through
Wednesday as the belt of trade winds east of the islands declines.
A fetch of stronger trade winds will expand east of Hawaii late
Wednesday and Thursday, boosting east shore surf back to around
March average. A small pulse of south-southwest swell is possible
on Tuesday, but otherwise, mainly background level surf will
prevail for south shores.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 AM HST Tuesday for west facing shores
of the Big Island.

&&

$$

DISCUSSION...TS
AVIATION...M Ballard
MARINE...Wroe


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