923
FXZS60 NSTU 200050
AFDPPG

Area Forecast Discussion
National Weather Service Pago Pago AS
150 PM SST Sun Jul 19 2026

.Short term [tonight through Tuesday night]...
High pressure to the south continues to generate breezy east-
southeasterly surface trade winds across American Samoa. However,
this area of high pressure and the trade winds associated with it
have begun to slowly weaken, leading to cancellation of the Wind
Advisory this morning. We will see a continued gradual weakening
of the trade wind pattern throughout the short term forecast
period, and by the end of the period wind speeds are forecast to
be decreased to a modest 5 to 15 mph.

This afternoon`s 00Z RAOB upper-air sounding revealed a shallow
moist layer with a strongly dry and stable trade wind temperature
inversion above it. Scattered passing trade wind showers can
still be seen in the area on satellite, but with cloud growth
being limited to below the stable layer, these showers should
continue to be shallow, light, and brief in nature. GFS forecast
proximity soundings for American Samoa indicate that the trade
wind inversion will hold throughout the short term forecast
period, making the likelihood of heavy or persistent rainfall
very low for this period.

.Long term [Wednesday through Sunday]...
A trough in the upper-level subtropical jet stream will move
across the region by midweek. This will lead to development of a
surface low pressure system passing south of American Samoa. This
surface low will disconnect American Samoa from the trade wind
generating ridge, and is forecast to fully end the trade wind
pattern, bringing light and variable winds on Wednesday.

The surface cold front associated with this weather pattern is
forecast to approach American Samoa by late Wednesday, with
American Samoa forecast to be on the cold side of the boundary by
Thursday morning. This is likely to bring well below average
temperatures late Wednesday night into Thursday as southerly
winds transport cooler air from near New Zealand into the
tropics.

As the pattern shifts, the aforementioned stable trade wind
inversion will erode, bringing a more moist and unstable profile
over American Samoa by midweek. A trough to the north will also
be allowed to drift closer to the area with the weakening of the
high pressure system, but is forecast to weaken significantly
before nearing the islands. The combination of a more favorable
atmospheric profile, upper-level forcing from the trough, surface
forcing along and near the cold front, and an additional trough
moving closer to the area from the north will culminate in an
increase in rain chances late Wednesday into Thursday. However,
at this time models are not very bullish on the potential for
heavy rainfall or flash flooding, with most models depicting more
of a light - misty type precip behind the cold front. This is a
trend that will be closely monitored going forward as heavy
uncertainty remains regarding the evolution of precipitation over
this timeframe.

As the trough and associated surface low move out of the area,
high pressure to the southwest will once again take over. This
high pressure system however, is forecast to be much weaker than
the current one. Winds are still forecast to turn out of the east
to southeast by late week into the weekend, but should be more
modest (around 5 to 15 mph).

&&

.Marine...
Wave and surf heights have slightly subsided today, with waves
observed around 9 to 11 feet at Aunu`u buoy and period times of
around 14 seconds. However, another south swell is expected to
again build surf to warning levels tonight into Monday due to
peak period times forecast to increase to near 20 seconds at
around midnight tonight. Therefore, the High Surf Warning has
been extended through Monday. The influence of this swell
combining with the breezy winds should continue to hold wave
heights in the 9 to 12 foot range through Monday, making marine
navigation difficult to dangerous. As both the swell and wind
speeds weaken throughout the remainder of the week, wave heights
will gradually subside, with both marine and surf conditions
expected to finally be below advisory levels by the end of the
week.

&&

.PPG WATCHES/WARNINGS/ADVISORIES...
Wind Advisory is cancelled.
High Surf Warning remains in effect.
Small Craft Advisory remains in effect.

&&

$$

Barton