Area Forecast Discussion Issued by NWS Honolulu, HI
000
FXHW60 PHFO 160200
AFDHFO
Area Forecast Discussion
National Weather Service Honolulu HI
400 PM HST Fri Mar 15 2024
.SYNOPSIS...
Moisture associated with an old front near the Big Island will
continue to bring showery weather to Maui County and the Big
Island, especially windward and mauka. Oahu will be on the
northern fringes of this moisture. A gradual trend toward fewer
showers and more sunshine is expected over the weekend as the
moisture slowly breaks up and moves south of the state. Trade wind
showers may increase again toward the middle of next week as a
strong trough aloft develops over the islands, but the lack of
deep moisture should limit shower coverage somewhat.
&&
.DISCUSSION...
A lingering stationary front over the Big Island is keeping
cloudy, gloomy, and showery weather over Maui County and the Big
Island today. A few spots on windward facing slopes of Maui and
the Big Island have received more than an inch of rain in the
last 12 hours. Surface observations, satellite animation, and the
00z soundings show there is a shallow layer of gentle-to-locally
breezy N to NE winds, with westerlies above about 5-7 kft. This
is helping to carry the tops of the incoming showers back over the
same areas, with broken to overcast cloud coverage. Oahu
continues to be near the northern fringes of this cloud shield.
The high resolution guidance is in good agreement that the slow
trend will continue to be toward decreasing showers for Maui
County and the Big Island overnight into Saturday, as moisture
associated with the frontal band gradually breaks up and perhaps
sags a little farther south. However, a weak mid-level shortwave
passing by just NE of the islands overnight tonight may help to
maintain enhanced showers for windward Big Island and the far
eastern coastal waters a little longer.
The aforementioned mid-level shortwave and tight height gradient
aloft is keeping the summits of Mauna Kea and Mauna Loa quite
windy, and recently CFHT gusted to 63 mph. Guidance shows winds
at the summits should peak this evening before dropping off on
Saturday as the shortwave moves away. Continuing to keep an eye
on trends in case an upgrade to High Wind Warning becomes
necessary this evening.
Drier and more stable air should move over the islands this
weekend, along with weak mid-level ridging. This should eventually
lead to quite a bit more sunshine and fewer showers, even for
windward and mauka sections. A weak surface high centered roughly
700 mi NW of Kauai this morning will move E and weaken further,
allowing for gentle to locally breezy trades this weekend.
Trades continue into early next week but a stronger mid-level
shortwave digs over over the islands as well. The global models
are showing a sharp trough aloft and another shot of unseasonably
cold air in mid-levels of the atmosphere by the middle of the
week. Interestingly, at the same time, the global model consensus
is that the airmass will also be relatively dry, with PWs from
about 0.8 north to 1.1 south across the state. So the trough
should be enough to keep some trade wind showers going as it puts
whatever moisture is available to work, but not as showery as
might typically be expected with a trough of that strength. Still,
this is far out in time so the details are definitely subject to
change.
Global models agree on a new surface high passing N of the
islands late next week. The high is expected to strengthen and
expand, dominating a large portion of the northeastern and north
central Pacific late next week. Looks like this will be our next
episode of windy trades.
&&
.AVIATION...
High pressure continues to build in from the west as a stationary
front near the Big Island weakens. Low level winds will gradually
veer from northwest to north-northeast over the next twenty-four
to thirty-six hours. Afternoon satellite and radar imagery
reveals a broad swath of low clouds extending from Oahu to
Windward Big Island. Occasional MVFR and isolated IFR conditions
are being reported along north facing slopes and coasts,
especially those of Maui and the Big Island.
AIRMET Sierra will remain in effect for occasional mountain
obscuration across Molokai, Maui, and Windward Big Island.
Continued improvement from the west is expected over the next
twenty-four hours, and Sierra will likely be canceled for Molokai
and West Maui by tomorrow morning. Mountain obscuration could
persist across portions of the Big Island through tomorrow night.
No other AIRMETs are in effect or anticipated at this time.
&&
.MARINE...
The weakening front is now stationary over the Big Island this
afternoon, continuing to enhance showers over the eastern half of
the state. High pressure to the northwest of the islands will
gradually drift eastward, resulting in moderate to locally strong
north- northeast winds through Saturday. Winds are expected to
remain mostly below Small Craft Advisory (SCA) thresholds through
early next week. Trade winds will veer out of the east and ease
into the light to moderate range this weekend, then hold through
the middle of next week as a new high builds northwest of the
islands.
A long-period, large to extra large northwest swell has been slowly
lowering at the nearshore PacIOOS buoys today. Surf heights have
dropped enough that the High Surf Warning (HSW) has been downgraded
to a High Surf Advisory (HSA) for the north and west facing shores
of the smaller islands, and north facing shores of Maui and extended
through Saturday afternoon. Due to the size and westerly angle, west
facing shores of the Big Island remain under a High Surf Advisory
(HSA) through Saturday as well. An SCA is also in effect for most
coastal waters zones due to the large swell. The declining swell
has allowed a few zones (mainly leeward waters) to drop out of the
SCA, due to seas dropping below 10 feet, however, the SCA has been
extended through tonight for the remaining waters. A reinforcing
northwest swell should arrive late Saturday night, keeping moderate-
sized surf along north and west facing shores through early next
week. Another long-period northwest swell reinforcement may push
surf up to HSA levels around Wednesday of next week.
South shore surf will remain tiny through Saturday. A south swell
arriving Sunday should produce a slight increase in the surf that is
expected to persist through Monday. East shore surf will also remain
small through early next week.
&&
.HFO WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory until 6 PM HST Saturday for N and W facing
shores of Niihau Kauai Oahu Molokai, for N facing shores of Maui,
and W facing shores of the Big Island.
Wind Advisory until 6 AM HST Saturday for the summits of Mauna Loa
and Mauna Kea.
Small Craft Advisory until 6 AM HST Saturday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters-Kaiwi Channel-Maui County Windward Waters-
Alenuihaha Channel-Big Island Windward Waters-Big Island Leeward
Waters.
&&
$$
DISCUSSION...R Ballard
AVIATION...Bedal
MARINE...TS