FXZS60 NSTU 200247 CCA
Area Forecast Discussion...CORRECTED
National Weather Service Pago Pago AS
347 PM SST Mon Feb 19 2018
.TONIGHT THROUGH WEDNESDAY NIGHT...Satellite shows heavy showers
and scattered thunderstorms just outside of Swains AOR. A surface
trough axis just north of Swains extends across Tokelau to SE
over north Cook Islands. GFS brings this trough closer to Manu'a
by Wednesday night, which will provide scattered showers and
possible thunderstorms near or above American Samoa starting
Wednesday evening. Interestingly, GFS materializes an upper-level
circulation well SE by tonight, then move toward the forecast
zones through Tuesday. As upper-level winds to the south
strengthens tonight...thunderstorms are possible during Tuesday
and Tuesday night. Hence, topographic effects will lead to diurnal
variation which will induce scattered showers before Wednesday
evening. Thus, anticipate light and variable winds to turn NE on
Wednesday night...and overnight temperatures will vary around the
mid to upper 70s.
.THURSDAY THROUGH MONDAY...Two main concerns are winds and showers
during the first two periods. An expected surface to mid-level
trough will bring numerous to occasional showers and possible
thunderstorms starting Thursday through Friday afternoon. GFS
shows this trough moving from NE to SW through Friday morning.
Perhaps, NNE winds will increase to 15 to 20 kt with higher gusts
on Thursday, then decline to 10 to 15 kt by Thursday night as
this expected trough moves farther SW of Tutuila. For now, will
keep an eye on this situation before making new updates as there
are many uncertainty after Saturday. Thus, will keep the previous
forecast the same.
.Marine...FNMOC Wave Watch III shows moderate seas of 5 to 7 ft
through the midweek. A long period SW swell up to 18 seconds will
arrive tonight, followed by a strong NW swell on Wednesday. Perhaps
these expected swells combined with fresh to strong winds associated
with the expected trough this Wednesday night will elevate seas
and surfs to near advisory levels through the rest of the week.
Thus, will monitor sea height data at PACIOOS Buoy near Aunuu for
a trend before updating seas and surfs.
.A Small Craft Advisory for Swains.