035
FXZS60 NSTU 230035
AFDPPG

Area Forecast Discussion
National Weather Service Pago Pago AS
135 PM SST Sat Aug 22 2026

.Short term [tonight through Monday night]...
A ridge of high pressure centered just north of New Zealand
should maintain steady southeasterly trade winds across the
American Samoa islands throughout the short term forecast period.
These winds are forecast to be breezy at up to 25 mph, but remain
just below Wind Advisory threshold (30 mph). Higher gusts may
also occur at times.

American Samoa is now experiencing Moderate Drought (D1)
according to the latest US Drought Monitor, with weekly rainfall
totals of less than one inch in four out of the past five weeks
and daily rainfall below the climatological average (0.21 inches)
each day since August 4. The 00Z RAOB upper-air observation
showed a trade wind inversion based near 850 mb, limiting
convective cloud growth to a shallow moist layer near the
surface. Latest satellite imagery confirms shallow cloud tops,
with light and short lived passing showers embedded within the
trades. Given the persistent inversion and limited moisture depth
that continue to limit rainfall, drier-than-normal conditions are
likely to persist throughout the short term forecast period.

.Long term [Tuesday through Saturday]...
The ridge of high pressure generating the southeasterly trades
will shift eastward by mid through late week. This will lead to
winds turning more easterly as the high moves to the southeast of
the territory. ECMWF and GFS guidance indicate wind speeds
decreasing by late Tuesday as this transition occurs.

Following the transition into an easterly flow regime,
Considerable uncertainty is present regarding the wind speeds and
rainfall pattern for the latter half of the week. The exact
positioning of the high pressure system and associated pressure
gradients will be critical over this period. Model and ensemble
guidance generally indicates stronger trade winds east of the
territory and weaker winds to the west, but with significant
differences in exact positioning. GDPS, UKMET, operational GFS,
and GFS ensemble all indicate wind speeds again increasing to
near Advisory levels over the latter half of the week. Meanwhile,
the ICON, operational ECMWF, and ECMWF ensemble keep winds much
more modest in the 10 to 15 mph range, with the stronger winds
displaced further east.

These differences in the wind pattern will also have a
significant impact on rainfall potential. Easterly winds
decreasing in speed from east to west creates "speed
convergence." Convergence forces air upward which creates more
favorable conditions for increased rainfall. UKMET, operational
GFS, and GFS ensemble are the most bullish for rainfall
potential, depicting the speed convergence creating a surface
trough axis near the territory. Meanwhile, other guidance keeps
the most significant rainfall activity north and west of the
islands. Regardless, increasing atmospheric moisture associated
with the transition to easterly winds should at the very least
bring more favorable conditions for passing showers.

Therefore, expect winds to shift from southeasterly to easterly
by midweek, with at least a slight increase in rainfall likely.
However, significant uncertainty remains regarding the strength
of the easterly winds and the magnitude of the increased
rainfall.

&&

.Marine...
Observations from the PacIOOS Aunu`u buoy have indicated wave
heights ranging from 8 to just over 10 feet since Wednesday night
as trade winds developed across the area. Large seas, Advisory
level surf, and increased rip current potential should persist
and potentially slightly increase through early Tuesday as trade
winds remain at a fresh breeze.

Marine and surf conditions are expected to at least briefly
improve on Tuesday night as wind speeds temporarily decrease into
a gentle to moderate breeze during the aforementioned transition
to easterly flow. However, seas will still be choppy at around 7
to 9 feet. Wave and surf heights beyond Tuesday night will be
heavily dependent on the aforementioned uncertainty in wind
speeds, but are likely to increase at least slightly.

&&

.PPG WATCHES/WARNINGS/ADVISORIES...
High Surf Advisory
Small Craft Advisory

&&

$$

Barton