Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 121322
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
322 AM HST Tue Mar 12 2024

.SYNOPSIS...
A stubborn upper level low will gradually weaken and shift east
today, allowing for a slow decrease in cloud cover, while winds
also weaken across the state. Showers will favor windward areas
this morning, then interior and leeward areas this afternoon.
Another disturbance aloft could bring some showers into leeward
areas late tonight and Wednesday, with light winds also bringing
a few afternoon showers to leeward areas Wednesday afternoon. A
cold front will usher in some cooler air and bring an increase in
showers to north and northeast facing slopes and coasts Wednesday
night through Friday as it moves through. Light to moderate trades
appear in store for the weekend, with rain chances remaining
highest over windward sections of the eastern islands.

&&

.DISCUSSION...
Currently at the surface, a 1028 mb high is centered around 1100
miles northeast of Honolulu, while a cold front is located around
900 miles west-northwest of Kauai. Moderate trade winds prevail
across the island chain early this morning, strongest over the
eastern end of the state. Infrared satellite imagery shows mostly
cloudy conditions across much of the state, with pockets of lesser
cloud coverage over the smaller islands. Radar imagery shows
scattered showers moving into windward slopes and coasts, with
mainly dry conditions in leeward locales. Main short term focus
revolves around trade wind trends and rain chances during the next
couple days.

The high northeast of the state will lift northeastward and
further away from the islands during the next couple days, as a
cold front approaches from the northwest. In response, the trades
will ease across the state today, with the winds likely being
light enough over the western islands and the more sheltered
sections of the eastern islands to allow for sea breeze
development this afternoon. Winds will ease further tonight with
land breezes common statewide by daybreak Wednesday, followed by
sea breeze development during the day. A cold front will then
gradually push southeast down the island chain Wednesday night
through Friday, ushering in moderate northerly winds which will
slowly shift northeasterly by daybreak Friday. The front will
stall out and dissipate in the vicinity of the Big Island on late
Friday through Saturday, while a weak high slides by to the north
of the state. Moderate northeast trades will hold on Friday,
before easing into the light to moderate range over the weekend.
High pressure north of the state could bring a slight increase in
the trade wind speeds early next week.

As for the remaining weather details, showers will favor windward
slopes and coasts this morning, with sea breezes allowing some
interior and leeward shower development this afternoon. Showers
should diminish fairly quickly this evening, with a few showers
still moving into windward and southeast facing slopes of Maui and
the Big Island. A shortwave trough approaching from the west may
draw some deeper moisture northward later tonight and early
Wednesday, increasing shower chances over leeward sections of the
smaller islands as southwesterly boundary layer flow gets a boost
from an approaching cold front. The shortwave trough is expected
to exit east of the state Wednesday afternoon, with sea breezes
bringing a few interior and leeward showers once again.

A cold front moving southeastward through the state will then
usher in some cooler air and bring increasing showers to north
and northeast facing slopes and coasts as it moves through
Wednesday night through Friday. Model solutions are showing some
differences in the progressiveness of the front Friday through the
weekend, lowering forecast confidence. Overall, it appears that
rain chances will remain highest over the eastern end of the state
Friday through the weekend as the front stalls out and dissipates
in this area, while the western islands may see very little rain
as the drier post-frontal airmass settles in.

&&

.AVIATION...
Light to moderate easterly trades will gradually weaken today as
high pressure north of the state moves east. Thus, afternoon
sea breezes will likely develop along coastal regions.

Trade flow in the lower levels will keep shower activity mainly
limited to windward areas this morning then transition to focus on
interior regions by afternoon. Expect patches of mid level clouds
today as an upper trough remains south of Hawaii.

Brief periods of MVFR ceilings and visibility will be possible in
any of the heavier showers.

AIRMET Tango remains in effect below 8000 feet over and south
through west of mountains for tempo moderate turbulence. These
conditions will likely improve later this morning. AIRMET Tango
also remains in effect for tempo moderate turbulence aloft between
120-FL280 for tempo moderate turbulence. See SIGMET PAPA series
over the islands for areas of severe turbulence between
Fl280-Fl350.

&&

.MARINE...
The high pressure system northeast of the islands will continue to
move farther east today as a weakening cold front approaches the
Hawaii region from the northwest. Wind speeds will blow from the
east-southeast direction today and diminish over the next few
days. Light to gentle westerly winds will filter into the region
from tonight through Wednesday ahead of the approaching front.
Land and sea breeze wind coverage will spread into near shore
coastal waters from this afternoon through Wednesday. Moderate to
locally fresh northerly winds will fill in as the front advances
down the island chain Wednesday night through Thursday night,
then winds will blow out of the northeast on Friday as the ridge
builds in behind the front. Gentle to moderate east to northeast
trade winds are forecast through the weekend.

Surf along exposed north and west facing shores will peak today
just below High Surf Advisory levels as a long period northwest
swell fills in. This swell will keep moderate surf heights along
north and west facing shores today and tonight, then trend
downward by Wednesday.

A more significant northwest to north-northwest swell is expected
to move into the islands late Wednesday night through the second
half of the week. Guidance shows a good sized area of gale- to
storm-force winds focused towards Hawaii within the 310-340 degree
directional bands lasting through Wednesday as the system moves
eastward. Surf heights will likely exceed warning levels during
the peak of this event from late Thursday through Friday, with
swell heights decreasing through the upcoming weekend. Another
overlapping moderate long period northwest swell will build in
this weekend, possibly peaking at low end HSA thresholds by
Sunday.

Surf along east facing shores will begin to ease through Wednesday
as the trade winds diminish. Surf along south facing shores
should gradually decline and return to background levels by
Wednesday as the current small south swell dissipates.


&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory until 6 PM HST this evening for Maui County
Windward Waters-Pailolo Channel-Alenuihaha Channel-Big Island
Windward Waters-Big Island Leeward Waters-Big Island Southeast
Waters.

&&

$$

DISCUSSION...Jelsema
AVIATION...Thomas
MARINE...Bohlin


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