639
FXZS60 NSTU 010055
AFDPPG

Area Forecast Discussion
National Weather Service Pago Pago AS
155 PM SST Fri Jul 31 2026

.Short term [tonight through Sunday night]...
A ridge of high pressure has continued to hold breezy east-
southeasterly trade winds and a stable trade wind inversion (a
warm and dry layer of air about 6000 feet agl observed via RAOB)
over the American Samoa islands throughout the day. Other
observations also highlight this stable pattern, with decreasing
cloud cover this afternoon and no rainfall observed today at the
WFO American Samoa office or any other rain gauges across Tutuila
island. This should keep rain chances low for tonight (~20%
chance). If any rainfall does occur it will be light and brief
passing trade wind showers.

The high pressure center of the ridge generating the trade wind
pattern is currently positioned to the southeast of the territory
and will continue to move eastward, and out of the area. This
will lead to a gradual weakening of trade winds and erosion of
the trade wind inversion over the weekend. A trough positioned to
the north of the territory may be allowed to drift slightly
closer to the islands due to the weakening of the ridge. However,
the trough is forecast to drift more westward than southward, and
therefore should be centered well to the west of the territory
this weekend. Still, by Sunday the trade wind inversion should be
completely removed over the territory as a light wind flow
briefly takes over. The trough, while not directly over the
islands, may still be close enough to bring some increase in
atmospheric moisture content. Overall, these factors will combine
to result in an increase in rain chances by the latter half of
the weekend. Flash flooding appears unlikely with no well-defined
trough directly over the territory. However, localized heavy
rainfall resulting in minor roadway and small stream flooding is
possible.

.Long term [Monday through Friday]...
A new high pressure system, currently off the east coast of
Australia, will be the next major weather system for the region
as it moves eastward into the Pacific Basin. This ridge will
begin building southeasterly trade winds across the territory
once again to start the new week. These trade winds should
initially be modest (around 15 mph) during early portions of the
week, with only slow and gradual strengthening anticipated
throughout the first half of the week. Any convergence in the
wind flow could bring increased rainfall, and potentially
localized flooding, given that a new trade wind inversion has not
yet developed and the environment remains moisture rich over the
Monday through Wednesday time frame (according to GFS proximity
soundings).

By mid to late week, more rapid strengthening of the trade winds
is expected. The high pressure center is forecast to move over
New Zealand, where the ridge will then rapidly strengthen. This
is forecast to bring southeasterly flow that could exceed Wind
Advisory criteria by the second half of the week. A trade wind
inversion is also likely to develop due to the increased ridging,
reducing the potential for heavy rainfall over the Thursday
through Friday time frame.

&&

.Marine...
Breezy trade winds have kept seas and surf elevated above
advisory levels today. Wave heights at the Aunu`u buoy were
observed in the 7 to 9 foot range throughout the day. However,
as trade winds weaken, seas and surf should gradually subside
below advisory levels over the weekend. Ideal ocean conditions
for small crafts, beachgoers, and other marine activities, should
then remain through at least Monday.

As southeasterly trades return next week, seas should begin
gradually building by Monday night through midweek. The
combination of gusty trade winds and south swells is forecast to
build wave heights to near 10 feet by Wednesday. Therefore,
expect advisory level seas and surf once again by midweek.

&&

.PPG WATCHES/WARNINGS/ADVISORIES...
A High Surf Advisory remains in effect through Saturday.
A Small Craft Advisory remains in effect.

&&

$$

Barton