459
FXZS60 NSTU 210120
AFDPPG

Area Forecast Discussion
National Weather Service Pago Pago AS
220 PM SST Tue May 20 2025

.DISCUSSION...
A line of convections associated with a trough just north of the
area was observed earlier in the day, and was anticipated to bring
showers, heavy at times with possible thunderstorms and gusty
winds over the islands. However, as the day progressed, satellite
imageries showed convections dissipating as they moved closer to
the islands. This was also reflected on the model data from last
night (20/12Z) and this morning (20/18Z). Upper air data (RAOB)
from this afternoon (21/00Z) shows a stable atmospheric profile
with minimal moisture content over the area. Also shown on the
latest satellite imageries is the main trough axis remaining to
the north of the area. Model data shows this trough migrating over
the area with heavy showers and thunderstorms by Wednesday
afternoon through the end of the week with breaks in between from
time to time. This may lead to flash flooding conditions over the
area.

Also shown on the latest model data is a broad high pressure
system centered over New Zealand, producing the moderate to fresh
trades, also holding the aforementioned trough over the area for
this time frame. Gentle to moderate trade winds will remain for
tonight through at least Wednesday night increasing to a fresh
breeze by Thursday through Friday.

The long term model data shows the aforementioned high pressure
migrating east as a weak low pressure system moves west-southwest
of the area, pulling in moisture from the east-northeast over the
islands on Saturday night through at least Sunday. This will
likely continue the flash flooding conditions for this time
frame. After the low pressure exits the region to the southeast, a
more favorable and calm weather pattern is expected for the new
week. Light and variable winds with isolated showers is expected
as another high pressure system moves south of the area.

&&

.Marine...
Latest observations from the PacIOOS buoy on the west (King-
Poloa) show seas around 5 to 7 feet with peak periods 16 to 18
seconds long. These conditions are evident in the manual
observations earlier in the day, and are translated to near high
surf advisory thresholds (10 ft). Winds also observed throughout
the day were around 10 to 15 knots with higher gusts at times.
However, model data shows a downward trend in seas and winds
for tonight through at least Wednesday night. By Thursday into the
weekend, trade winds will pick up to a fresh breeze turning east
on Friday afternoon. By this time frame also, a large south swell
is expected to reach coastal waters and linger through at least
Saturday. Long term model data show seas around 5 to 7 feet
remaining for the rest of the forecast period (5 days) as winds
also decrease to a more gentle north flow on Sunday. Will
continue to monitor conditions and issue alerts as more data
becomes available.

&&

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

&&

$$

JTAllen