Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
858 PM EDT Tue Jun 16 2026
Day 1
Valid 01Z Wed Jun 17 2026 - 12Z Wed Jun 17 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE TEXAS GULF COAST THROUGH THE LOWER MISSISSIPPI VALLEY...

01Z Update...
Focus for excessive rainfall overnight continues to be along the
Gulf coast states from Texas eastward into parts of Florida and
Georgia. Main concern continues to over parts of Louisiana which
lie along the the path of of Potential Tropical Cyclone One and
where cyclonic flow around PTC 1 can enhance rainfall amounts by
tapping and transporting Gulf moisture on-shore. Main changes in
this outlook were to trim the northern portion of the higher
categories. The latest deterministic and ensemble runs as well as
the HREF and HRRR were struggling to develop QPF north of a quasi-
stationary front extending from the southern Appalachians to
northwest Arkansas and southwestward to the international border.

Bann

...16z Update...
Ongoing convection with rain rates of around 1-2"/hr, increasing
trends on 24 hour rainfall totals as well as a consolidation in
areal placement of max QPF support an elevated moderate risk area
(at least 55% chance) of excessive rainfall over portions of
central/southern Louisiana stretching into southwestern
Mississippi. Otherwise, the western section of the outlook area
remains mostly untouched. The presence of the tropical surface wave
along the south Texas coast throughout the day maintains the
possibility of scattered convection capable of high rain rates
occurring.

The latest CAMs continue to signal potential for diurnal convection
capable of high QPF output over southeast Florida late this
afternoon/evening. Therefore, the marginal risk area will be
maintained.

Kebede

...Previous Discussion...
An impressive and dynamic setup with multiple mesoscale features
is expected to develop through the day today from the Texas Gulf
Coast through the lower Mississippi Valley. The most rainfall for
the day will occur through this morning. A tropical disturbance
over Deep South Texas will support the strengthening of the typical
diurnal low level jet out over the Gulf, driving a plume of
impressively deep tropical moisture northward into the Texas and
Louisiana Gulf Coasts. Meanwhile, a stationary front currently
over southern Arkansas and northern Mississippi will advance
southward as a cold front due to a disturbance and push of cooler
drier air south behind the front. This clash of air masses will
result in continued upscale development of storms that have broken
out over northern Louisiana through the overnight and into Tuesday
morning. FFGs are already lower in many spots west from the western
tip of Mississippi. This nearly stationary line of training storms
is likely to persist well into the afternoon, which could make for
a narrow but nevertheless severe area of very high totals of storm
total rainfall, especially into western Mississippi. Guidance has
suggested this narrow corridor, highlighted in much of the guidance
since yesterday along the I-20 corridor has now shifted a few
counties south, extending from Alexandria, LA east almost to
Hattiesburg, MS. The inherited Moderate Risk for this area was
trimmed on the north side both with the current start of convection
in this corridor and the southward trend in the guidance.
Meanwhile, a number of other pieces of CAMs guidance suggest that
the showers and storms developing along the immediate coast roughly
from Galveston/Trinity Bays east to Lafayette, LA will be the
primary and dominant line of showers and storms impacting the
northwestern Gulf Coast today. This line would from largely from
sea breeze/frictional convergence of the strong onshore southerly
flow into the coast. The front to the north may play a role in
maintaining the storms where they are, but would likely play a
secondary role. Should this line develop robustly, it will force
the aforementioned line of storms over northern LA/southwest MS
eastward, resulting in less rain over northern/central LA. Most
likely there will be a combination of the two, with the east-
northeastward moving storms along the southwest Louisiana coast
continuing with the line to the northeast over western Mississippi.
Once again the Moderate Risk here remains in place with few
changes.

Finally, further south along the Texas Gulf Coast, the larger
synoptic level disturbance, responsible for the heavy rains and
flash flooding over Deep South Texas yesterday will likely eject
east into the Gulf today. As it does so, it will create localized
bands of heavy rain along the Middle Texas Coast, which will then
advect northeast to join the line east of Houston. This area from
Corpus Christi to Houston remains the most uncertain portion of the
Moderate Risk area, as a small south/east shift in the track of the
disturbance will take the lion's share of the associated rainfall
ahead of the low track out over the open Gulf, and greatly limit
any rainfall today along the coast. The inherited Moderate Risk was
trimmed completely south of Corpus Christi, with just a Slight
along the immediate lower Texas Gulf Coast to account for ongoing
rains in the area. The threat will shift off the coast by late this
afternoon.
With all three areas of heavy rain above, they will all diminish
and dissipate as a significant heavy rain threat by this evening.
Occasional showers and a storm or two may impact the immediate Gulf
Coast through the overnight, but for the most part the heavy rain
threat through tonight should be minimal.

Wegman


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt