310
FXHW60 PHFO 220630
AFDHFO

Area Forecast Discussion
National Weather Service Honolulu HI
830 PM HST Sat Sep 21 2024

.SYNOPSIS...
Trade winds will decrease Sunday and Monday as the surface ridge
to our north weakens. Rainfall will favor windward and mauka
locations but a few showers, some heavy, may develop across
leeward areas as an upper disturbance moves by. Breezy trades and
more stable conditions are expected to return on Tuesday.

&&

.DISCUSSION...
A surface ridge far north of the main Hawaiian Islands is driving
locally breezy trades across local waters this evening. Models
show winds should begin to gradually decrease tonight as the
ridge weakens and drifts southward. An upper low north of Kauai
has had minimal effect on local weather so far, but as it digs
southward tonight the inversion will lift and weaken. As a result,
mainly windward showers may become a bit heavier than the past
few days. A narrow and diffuse band of moisture in the trades will
likely bring higher shower coverage from Maui to Oahu overnight.
Expect slightly weaker trades and heavier showers Sunday and
Monday.

Expect stronger and more stable trade wind flow by midweek.
Locally breezy trades will be driven by a tighter pressure
gradient between the strengthening surface ridge to the north and
a pair of tropical disturbances passing several hundred miles
south of the islands. The upper low will fill and drift away to
the west, and a ridge aloft building in from the east will bring
stability. Models differ on timing but show a pocket of moisture
in the building trades passing over the islands late Monday and
Tuesday. This will likely be too late for enhanced rainfall and is
expected to produce typical windward showers. Through the rest of
the work week, tropical moisture that could clip the Big Island,
but expect typical windward rainfall for most islands.

&&

.AVIATION...
Moderate to locally breezy trades will weaken slightly heading
into Sunday with scattered showers will favoring windward and
mountain areas. With temperature inversion heights expected to
remain elevated and weaken heading into Sunday as an upper level
low approaches from the north, expect brief moderate to heavy
downpours in showers with some spillover into leeward areas. MVFR
conditions possible heavier showers. AIRMET Sierra may be needed
for mountain obscuration for windward locations during the
overnight hours.

AIRMET Tango is in effect for tempo moderate turbulence between
FL200 and FL400 over the islands tonight. This AIRMET will likely
be needed through Sunday morning.

&&

.MARINE...
Fresh trade winds will ease slightly as a cold front passing
through the far northern Central Pacific basin weakens the ridge
north of the island chain. passing ridge to the north of the
islands weakens. Winds will remain below Small Craft Advisory
levels through Monday. The trade will strengthen back to moderate
and locally strong levels from Monday night onward through the
remainder of the upcoming work week.

Surf along north and west facing shores will remain tiny through
Monday. A moderate, long-period northwest swell will arrive on
Tuesday and push surf along north and west facing shores well
above seasonal average, though below High Surf Advisory levels,
Tuesday night and Wednesday. This swell will decline as it shifts
out of the north-northwest on Thursday, then fade on Friday.

Surf along south facing shores will remain just below seasonal
average over the next couple of days as an inconsistent southwest
swell moves through. A reinforcing southwest swell is expected late
Monday into Wednesday. With trade winds on a decline, east shore
surf will be well below seasonal average during the next few days
with increasing trends by Tuesday night or Wednesday.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Powell
AVIATION...Foster
MARINE...Bohlin