FOUS30 KWBC 050757
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
357 AM EDT Mon Oct 5 2026

Day 1
Valid 12Z Mon Oct 05 2026 - 12Z Tue Oct 06 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE SOUTHERN
LOWER TEXAS COAST...

...Lower Texas Coast...

A Slight Risk of excessive rainfall was maintained for coastal
Willacy and Cameron Counties, including Brownsville, with this
update. A stalled out front remains draped across almost the entire
Gulf Coast. The portion of the front near the Lower Texas Coast
remains stationary. Flow on both sides of the front remains out of
the northeast. An abundance of tropical moisture remains across the
entire Gulf. Thus, along the front, PWATs are above 2.25 inches.
This abundance of moisture and instability from the hot surface
water across the Gulf with SSTs in the upper 80s are fueling slow-
moving and training showers and thunderstorms that are moving
southwestward along the front and into the Lower Texas Coast.
Rainfall amounts yesterday alone ranged between 3-6 inches, and an
additional 2-4 inches are expected today. However, outside of some
urban areas on S. Padre Is. and Brownsville, most areas are flat
and with sandy soils, making them very difficult to flood, even
with the abundance of rainfall seen and expected. Thus, a Slight
Risk was maintained for this region, particularly for those
aforementioned urban areas.

...Southeast...

The same front impacting the Lower Texas Coast extends across far
southern Alabama, Georgia, and north Florida. Unlike back in Texas,
this front has been moving south, albeit slowly. The same features
as in Texas are in place in the Southeast. An unseasonably moist
air mass is south of the front over much of Florida, and a
seasonably dry one is north of the front. This clash of air masses
is allowing for shear which is supporting slow-moving and training
thunderstorms. The heaviest rains will be towards the Florida
Panhandle near Apalachicola and the Big Bend Region. Fortunately,
this area is relatively sparsely populated, flat, and has numerous
swampy areas, all of which work against flash flooding. Thus,
despite some forecast totals for the day in the 3-6 inch range for
those regions, the area remains in a Marginal Risk as flash
flooding in this area should remain isolated. Urban flash flooding concerns
will remain along I-10 from Pensacola through Tallahassee and into
Jacksonville. Since the storms are unlikely to move very far, the
overall flash flood threat will remain isolated.

Wegman
 

Day 2
Valid 12Z Tue Oct 06 2026 - 12Z Wed Oct 07 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE LOWER
TEXAS COAST, FAR SOUTHERN GEORGIA, AND MUCH OF FLORIDA...

...Lower Texas Coast...

The stalled out front over the northern Gulf will continue to
funnel moisture into coastal Willacy and Cameron Counties on
Tuesday. Guidance suggests that unlike previous days, much of the
rainfall on Tuesday will remain off the coast, with only a small
fraction of the total rainfall making it into the coast as far west
as Brownsville. For this reason, and the difficulty even with
abundant moisture to get flooding in this region, the prior day's
Slight Risk was dropped to a Marginal risk for Tuesday, which is no
change from the inherited forecast.

...Florida and Georgia...

A very slow-moving front will continue sagging south on Tuesday,
largely aimed at the northern Florida Peninsula, though some early
morning rain may still impact extreme southern Georgia. As on prior
days, any flash flooding will likely be constricted to urban and
poor-drainage areas, representing an isolated threat. It remains
possible that should a slow-moving or training storm move over a
more urban area, such as Jacksonville, that a localized more
significant flash flooding threat could emerge. Other than some
minor tweaks, mostly on the southern end of the Marginal over south
Florida, the forecast for Tuesday remains unchanged.

Wegman
 

Day 3
Valid 12Z Wed Oct 07 2026 - 12Z Thu Oct 08 2026

...THERE ARE MARGINAL RISKS OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE FLORIDA PENINSULA, THE LOWER TEXAS COAST, AND SOUTHWEST TEXAS...

...Florida...

The front over the middle of the Florida Peninsula will end it's
slow southward movement on Wednesday and stall out over the area.
Fortunately, with the front no longer providing forcing for storms,
any rainfall will be driven by cold pools, proximity to other
storms, and localized pockets of higher instability. The point is
that there will be no organization to the convection, so the flash
flooding threat will remain Marginal, contingent on heavy rain
impacting an urban or poor-drainage area.

...Lower Texas Coast...

A rinse-and-repeat pattern continues on the Lower Texas Coast.
Easterly flow off the Gulf will continue to advect plentiful
tropical moisture westward across lower south Texas. Marginal
instability and a lack of forcing will remain factors working
against a higher flood threat, despite saturated soils. No changes
were made to the ongoing Marginal Risk for this area.

...Southwest Texas...

Upper level vort maxes tracking along the TX/Mexican border in
southwest Texas associated with a positively tilted trough may
allow afternoon convection to develop in a very flash flood prone
area of Texas around the Big Bend, perhaps as far northwest as the
El Paso metro area. Instability will be lacking so any showers and
storms will have to impact the right place to cause flash flooding.
The inherited Marginal Risk introduced yesterday afternoon remains
with no changes.

Wegman
 

Day 4 and Day 5
Valid 12Z Thu Oct 08 2026 - 12Z Sat Oct 10 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE GULF COAST & TEXAS BIG BEND...

A stationary front will remain draped across the Gulf through late
week as a general weakness in the mid-level flow persists. To the
west, an amplifying closed low will move across parts of West
Texas, helping to maintain downstream jet streak development to
place favorable RRQ diffluence atop the Gulf. These two features
combined with instability over the Gulf will result in deep layer
ascent to support rounds of convection, with rainfall rates of
2-3"/hr possible thanks to anomalous PWs of around 2.25", or above
the 90th percentile according to NAEFS. There is the typical
uncertainty at this time range as to how sharp the instability/PW
gradient will be along the Gulf Coast, but most of the global
models and the accompanying ECENS/GEFS ensembles suggest
significant rainfall potential along the immediate coast, some of
which will occur atop sensitive soils from recent heavy rainfall
leading to at least isolated instances of flash flooding. It is
important to note that the AI models are both a bit farther south
and slower bringing QPF onshore Thursday, but for now the inherited
MRGL risks were mostly unchanged on the Gulf Coast.

Late Thursday night and on Friday, as the upper trough deepens over
West Texas, the resulting downstream ridging will help push a wave
of low pressure northward across the Gulf, for which NHC currently
has a 50% chance of development. Regardless of development of this
feature, a rapid increase in moisture will surge northward leading
to a greater probability for heavy rainfall along portions of the
central Gulf Coast, supported by strengthening 850mb winds
converging onto the coast. There is still considerable latitudinal
uncertainty, but the GEFS/ECENS/NBM probabilities all indicate a
10-20% chance of at least 3" of rain Friday, driving the new MRGL
risk across the Gulf Coast.

Farther west, a mid-level vorticity max/trough will deepen into a
closed low across Texas. This will manifest within a region of
increasing column moisture as flow advects westward from the Gulf,
which is reflected by GFS PW anomalies reaching +1 sigma and deep
moist-adiabatic lapse rates noted in regional forecast soundings.
Weak forcing beneath this amplifying trough/low will force slow
storm motions in a region of 20-30 kts of bulk shear to promote
scattered convective clusters with rainfall rates 1-2"/hr. While
there is considerable uncertainty as to the spatial coverage of
thunderstorms both Thursday and Friday, this setup will support at
least an isolated risk for flash flooding from the Texas Big Bend
into the Edwards Plateau.

Weiss
$$
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