National Weather Service United States Department of Commerce



FXZS60 NSTU 250113 CCA

Area Forecast Discussion...CORRECTED
National Weather Service Pago Pago AS
213 PM SST Sun Jan 24 2021

The monsoon trough to the south has slightly shifted northward
and edging closer to the territory. Satellite imageries show
deeper convections to the far northwest and southeast of the
islands, associated with the monsoon trough. However, the latest
model solutions (24/18Z) show the trough lingering just south of
the AOR for the duration of the forecast period. Models also show
a ridge building from the north holding the trough away from the
territory. With the trough and ridge juxtaposed, the instability
(converging winds and convective environment is likely to increase
the chances of precipitation and gusty northerly winds over the
islands. Flash flooding conditions to take place in the short
term forecast period is highly favorable. Expect numerous to
frequent showers, heavy at times with isolated thunderstorms and
moderate to fresh northerlies tonight through Monday turning
northeasterly Monday night through the rest of the forecast

Additionally, the model shows a couple of low pressure systems
embedded within the trough. The potential for one of these low
pressure systems to deepen by midweek is high. However, model
data shows this low pressure system to develop and move across the
Fiji Islands and continue moving south. Although model data gives
this scenario for the week, it is likely that weather patterns may
shift (i.e. the aforementioned ridge may be too weak to hold the
trough south of the area) and change the course of any systems.
Therefore, will continue to monitor conditions as more data
becomes available.


The Wave Watch III latest data show combined seas of 4 to 6 feet
lingering tonight. A northerly swell of 5 to 7 feet will reach
American Samoa coastal waters Monday and will further build to 7
to 9 feet with long periods (15+ seconds) Monday night through
the midweek. These seas and surfs will likely be enhanced by
moderate to fresh northerlies tonight. Therefore, advisory for
small crafts is now in effect and the advisory for high surfs will
be issued as prompted when criterias are met, especially for the
north and west facing shores.


A Small Craft Advisory is in effect.
A Flash Flood Watch is in effect.