Area Forecast Discussion Issued by NWS Honolulu, HI
000
FXHW60 PHFO 170639
AFDHFO
Area Forecast Discussion
National Weather Service Honolulu HI
839 PM HST Sat Mar 16 2024
.SYNOPSIS...
Moderate northeast trades will shift out of the east overnight
into Sunday, then linger through the first half of the week.
Despite the drying trend from west to east, moisture lingering
over the eastern end of the state from a recent front will support
mostly cloudy skies along with a few showers holding into Sunday
over windward areas before scattering out by the end of the
weekend. Otherwise, mostly dry and stable conditions are
anticipated through the first half of the week, with the best
rainfall chances favoring windward and mauka areas overnight. A
return of breezy easterly trades and increasing rainfall chances
are possible through the second half of the week as an upper
disturbance moves into the area.
&&
.DISCUSSION...
Satellite imagery showed a band of low-level moisture and clouds
lingering across the eastern end of the state due to a frontal
boundary that recently moved through. Despite the cloud coverage
in these windward areas, just a few showers are shown moving
through this evening, with just a few hundredths recorded at the
rain gauges in the past few hours. Expect this trend to persist
into Sunday before the drier air spreads into the area and the
clouds begin to scatter our. Elsewhere, dry air and stable
conditions are anticipated overnight.
Guidance remains in good agreement and shows dry and stable
conditions continuing through the first half of the week as upper
heights rise over the region and the aforementioned moisture near
the Big Island moves out. This will support a more suppressed
environment with PWs remaining around an inch or less. Trades will
shift out of the east beginning Sunday and hold at moderate
levels. The best chances for a few showers will be over the
typical windward and mauka locations overnight through the early
mornings. The best chance for any leeward showers will come
through the afternoons where localized sea breezes manage to form.
A gradual strengthening and destabilization of the trade wind
flow is possible Wednesday into Friday. Confidence is higher that
trades will likely increase as a deeper surface high sets up far
north of the state, with breezy conditions possible by Friday. An
upper-level trough will slowly pass over the region during this
time, bringing 500 mb temperatures as low as -16C on Wednesday
night and Thursday. While there could be some increase in shower
activity in response to the added instability, a mid-level ridge
may be able to maintain stability and lower the chances of heavy
rainfall.
&&
.AVIATION...
High pressure continues to build over the western end of the
state, but deep moisture persists across Maui and the Big Island.
Occasional MVFR conditions in showers are expected to persist
across Windward Big Island through tomorrow morning and possibly
beyond. AIRMET Sierra for mountain obscuration remains in effect
for northeast facing slopes of the Big Island, and may need to be
extended to included East Maui later tonight. VFR conditions will
prevail across the remainder of the state.
Meanwhile, moderate to locally breezy trade winds will return to
the islands by tomorrow afternoon. This will usher in drier air
that will help improve conditions across Maui and the Big Island.
It may also generate occasional moderate mechanical turbulence
downstream of higher terrain if winds at summit level are
sufficiently strong enough.
&&
.MARINE...
Moderate northeast trades will shift out of the east overnight
through Sunday, then linger through the first half of the week.
Stronger trades may return toward the end of next week as high
pressure builds north of the islands.
The current near 5 to 7 foot, medium period northwest (330
degree) swell will continue to slowly fall through Tuesday. A
reinforcing moderate size, longer period northwest (310 degree)
swell should begin arriving later tonight into early Sunday
morning. This swell should be enough to push already slightly
elevated surf up a notch to High Surf Advisory (HSA) levels along
north and west-facing shores late Sunday through a good part of
Monday. The arrival of a significant moderate size, long period
northwest (310-330 degree) swell late Tuesday and Wednesday will
likely maintain solid mid week advisory level surf with a late
week decline to below HSA heights by early Thursday. A slight
boost to south surf is expected Sunday through Tuesday as a small,
long period south (200 degree) swell moves around the islands
through Tuesday. East shore surf will remain small through early
next week with a slight pick up in chop anticipated later in the
week with strengthened trades.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION...Gibbs
AVIATION...Bedal
MARINE...Blood