Dangerous Heat in the Central and Southern U.S.; Thunderstorms and Heavy Rain in the Northern Plains

Dangerous, prolonged heat is expected across portions of the Central and Southeast U.S. through July. Scattered severe thunderstorms are expected over parts of the northern Plains into the upper Mississippi Valley Tuesday, with damaging winds and large hail as the primary threats. Heavy rainfall could lead to areas of flooding across the northern Plains, Upper Midwest, Southeast and Southwest. Read More >

179
FXZS60 NSTU 220107
AFDPPG

Area Forecast Discussion
National Weather Service Pago Pago AS
206 PM SST Mon Jul 21 2025

.Discussion...
A weak trough to the north-northeast currently over the Manu`a Islands and
moving closer to Tutuila and Aunu`u are shown on the lateset satellite
imageries. This trough is expected to bring scattered to numerous showers,
heavy at times for tonight through at least Tuesday night. Upper air
observations (RAOB) from this afternoon (22/00Z) shows a more stable
atmosphere with an inversion at the 850 to 750 mb levels. These conditions
reflects the satellite observations and latest model solutions, keeping
moisture content concentrated close to the surface. The RAOB observations
also show that showers embedded within the trough will likely be short-lived.
This trough is expected to dissipate by Tuesday night. However, another round
of showers associated with another trough is expected to move over the area
by late Thursday night through the weekend. This second trough may produce
flash flooding conditions over the islands as it moves further south.
Furthermore, a high pressure system to the southwest will move south of
the islands as it pushes the latter trough back, over the islands, sustaining
showers for the rest of the forecast period.

Therefore, expect scattered to numerous showers increasing to widespread with
light and variable winds for tonight through Friday, increasing to moderate to
fresh east breeze by Friday night through the new week.

&&

.Marine...
Ideal ocean conditions are observed across the coastal waters as
seas continue to remain below advisory thresholds. Observations from
the PacIOOS buoys near Aunu`u and Poloa show seas around 4 to 6 feet
with intemittent periods of more than 10 seconds peaking at 15 seconds
long. With these heights and periods, the enhancement of surfs in some
areas is possible. The latest model data show seas subsiding further
to around 3 to 5 feet with periods less than 10 seconds on Tuesday
through at least Thursday. By Thursday night into Friday, seas will
slightly build to 5 to 7 feet, with periods increasing to more than
10 seconds. Observations of long period show an increasing trend
of surfs as waves get closer to shore, and increasing the risk of
strong rip currents. Model data also shows a large south swell reaching
American Samoa coastal waters by the end of the week. This south swell
also aligns with winds increasing at this time frame. Light and variable
winds will prevail for tonight through at least Friday, increasing
to a moderate to fresh east breeze by Saturday night.

&&

.PPG WATCHES/WARNINGS/ADVISORIES...
NONE

&&

$$

JTAllen