Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
314 PM EDT Sun Oct 4 2026
Day 1
Valid 16Z Sun Oct 04 2026 - 12Z Mon Oct 05 2026
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE LOWER TEXAS COAST...
...Lower Texas Coast...
16Z Update: Radar and satellite composite continue to point to an
active morning and afternoon for areas of the lower Texas coastal
plain to areas inland, down towards the lower RGV and the
population centers. Recent trends have noted an uptick along the
immediate TX coast in Kennedy county down towards northern Willacy
leading to rainfall rates between 1.5-2"/hr at peak intensity. This
continues to overlap areas that were hit flush overnight into the
early morning hours leading to likely some flooded areas across the
King Ranch domain. Radar estimates from the MRMS gauge corrected
data source indicate an area of 3-6" has already fallen across the
eastern portions of Kennedy county with a swath of 1-3" located
south of the area. This trend will continue allowing for an
elevated flood risk over the entire stretch from Kennedy county
down into Brownsville with a western inflection towards McAllen and
all areas in-between. Highest risk for flash flooding will continue
to be those urban zones littered across Deep South TX, including
the metro area between Brownsville-McAllen, as well as potential
for places like Harlingen and Raymondville. HREF neighborhood
probabilities for >5" of rainfall for the event continue to be
elevated across Kennedy county down towards Port Mansfield, but
there remains a sharp western edge to the threat with more modest
probs for >2" and >3" available further back into those population
centers.
Maintained the MDT risk given the ongoing heavy rain signal across
the region, but anticipating a slow degradation of the threat
later this evening into the overnight hours with a bit more of a
scattered heavy rain forecast for the region after 00z. For more on
the current setup across the area with the ongoing heavy rain into
the lower Texas coastal plains, please refer to MPD #1441.
...Southeast U.S...
16Z Update: Quasi-stationary front extending from the coast of TX
into the southeastern U.S. will continue to slow press south as
more stable air wedges down east of the Appalachian front creating
a textbook damming signature across the Carolina Piedmont into
northeastern GA. 12z surface analysis and regional observations
indicate the frontal alignment through the SC Midlands extending
into the vicinity of Augusta, GA and off to the northeast,
extending just beyond North Myrtle Beach within the past few hours.
This trend will continue leading to a sharp cutoff on the northern
periphery of the better convective environment with the best threat
for heavy rainfall located along and south of the front during its
progression. Assessment of regional theta_E's tells a big story on
the frontal positioning, along with the available instability for
the deep layer moisture to tap into during traditional diurnal heat
flux late-morning through the afternoon and evening hours. Current
progs are for scattered convection with likely heavy rain cores
stemming from the PWATs sufficiently above 2" across much of the
Southeast U.S, mainly south of the front. Prevailing southerly flow
around a ridge positioned over the FL Peninsula will serve as a
mechanism for continued to moisture advection and sending some of
these waves of mid-level energy out of the adjacent Gulf into the
coastal plain LA over into the FL Panhandle.
PWATs from the 12z sounding out of KLIX indicated climatologically
anomalous moisture pooling over the immediate central Gulf Coast
with values up around 2.5", a solid 95-99th percentile for the
date and month, respectively. Coupled with the energy slowly
advancing out of the Gulf and elevated instability located along
and just over the nearby Gulf waters, cases of heavy rainfall have
continued to plague areas from southeastern LA over into the
western FL Panhandle. Multiple flash flood warnings were issued
this morning over near Destin/Fort Walton Beach with a surge of
heavy rainfall stemming from the advection regime off the Gulf.
Current radar indicates a band of heavier rain impacting southeast
LA into southern MS, a signal that has been prevalent from much of
the CAMs this morning. Expectation is for this threat of locally
heavy rainfall to continue through the afternoon and evening hours
with scattered instances of flash flooding noteworthy for those
urban areas along I-10 to the coast. Rainfall rates between 1-3"/hr
are likely in any of these stronger convective cores thanks to the
anomalous deep layer moisture with the 12z RAOB sounding indicating
tropopause levels up towards 150mb, a signature normally seen with
tropical airmass types. So long as we maintain persistence in this
setup, there remains an elevated threat for flash flooding in this
region of the CONUS, extending inland into southeast AL and
southern GA over towards the SC/GA coastal plain. HREF EAS
probabilities for >2" remains solidly above 20% from the bayous of
southeast LA over into the corridor from Hilton Head, SC to near
Jacksonville, FL. A general max prob is situated over the western
FL Panhandle with a "bullseye" of 40-60% located between Pensacola
to Panama City Beach. This is the area where the opportunity for
more appreciable totals >4" for the event could spell multiple
chances for flash flooding given the urban density factor.
A broad SLGT extends from the coast of LA to FL/GA and points north
into central AL/GA as the environment in this area remains
favorable for heavy rain prospects as the front slowly makes its
progression into the area over the course of the period and the
eventual D2. A high-end SLGT remains forecast from Biloxi to
Tallahassee with a northern bound centered over southeastern AL
into southern GA to the GA coast. This is the area where heavy
rainfall potential of 2+ inches per hour are most likely given the
latest HREF hourly probabilities, enough to enhance flash flooding
in any urban corridor in this region, as well as the clay hills of
southern GA.
Kleebauer
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
314 PM EDT Sun Oct 4 2026
Day 2
Valid 12Z Mon Oct 05 2026 - 12Z Tue Oct 06 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE LOWER TEXAS
COAST...
...Texas Coast...
20Z Update: Current trends in guidance have increased confidence in
a locally enhanced area of flash flooding potential with a
positioning over more of the urban corridor in the lower Rio Grande
Valley (RGV) compared to the current D1. Models have picked up the
signal with a relative maxima positioned over Willacy and Cameron
counties, including the city of Brownsville and surrounding urban
corridor located between McAllen to Brownsville proper. HREF and
REFS blended mean QPF is right around 5-8" over the region, albeit
falling over an entire period, meaning scattered flash flood
prospects likely with potential for more significant flash flood
scenarios pending training of heavier cells located in the region.
The flow will remain persistent out of the east-northeast allowing
for pivoting bands to rotate back over the same areas for hours
before they subside. PWAT percentiles remain closer to the 99th
percentile according to the latest ECENS and NAEFS probabilistic
outputs for all of Deep South TX. This points to a maintenance of
the SLGT risk with a non-zero chance at a future upgrade if
guidance/radar trends warrant.
Kleebauer
..Previous Discussion..
A surface front will track southward into the Gulf Sunday and
linger along the Lower Texas Coast Monday. While the accompanying
ribbon of instability may be quite compressed by Monday, PWs as
high as 2.5" and deep warm cloud depths will maintain a favorable
thermodynamic environment for heavy rainfall. Additionally, an axis
of 700-500mb deformation just offshore will arc back towards the
region, resulting in a narrow corridor of enhanced ascent to drive
streaks of convection with heavy rain. The HREF (when available)
and REFS both indicate a 20-30% chance of rainfall rates exceeding
2"/hr, which through training thanks to continued anti-parallel
Corfidi vectors may produce an additional 3-5" with locally higher
amounts (REFS/HREF 5"/24hr probabilities above 60%). For this
reason a SLGT risk has been added for a narrow corridor of the BRO
CWA.
Weiss
...Southeast...
20Z Update: Ther overall forecast remains consistent with the
latest guidance outside some small adjustments on the northern
fringe of the inherited MRGL risk. Models and latest observations
in the current D1 relay a theme of the frontal progression being a
little faster and the wedging east of the Appalachians digging a
bit further south into GA during the D2 time frame. HREF and REFS
probabilities for >3" are highest within bounds of the front,
especially in the coastal areas of FL where 50-80% probabilities
for the threshold are present along the northeastern FL coast,
including the Jacksonville to St. Augustine area. Main threat will
continue to be the urban centers and areas with a history of poor
drainage. PWATs will continue to reside above 2" for much of FL
into southeastern GA, however with the frontal progression, the
best threat for heavy rain >2" will reside over north FL as noted
via the hourly rate probabilities from both hi-res ensembles
(HREF/REFS) between 20-50% on an areal average during the forecast
cycle.
Kleebauer
..Previous Discussion..
A similar environment persists farther east along the Gulf Coast
from the Florida Panhandle and extending northeast into coastal
South Carolina. A cold front will be drifting slowly southeast
across this area as height falls south of an expansive mid-level
trough inexorably work their way south towards the Gulf Coast. Weak
impulses moving through the flow aloft will help generate waves of
low pressure along this front, and where these waves move northeast
they will enhance the rainfall through locally accelerated flow and
stronger ascent. Regardless, efficient rainfall rates of 2-3"/hr
are likely within a plume of exceptional tropical moisture (PWs
above 2.25") and deep warm cloud depths. Considered a SLGT risk
where the guidance supports areas of heavier rainfall, but there
continues to be some uncertainty as to how much instability will
persist north of the front (depending on how far south it
progresses), and anafrontal rainfall may not be heavy enough for a
SLGT risk upgrade. While training is likely along the CAPE
gradient which through these rain rates could lead to 2-4" of rain
atop saturated soils from D1, opted to maintain the MRGL risk at
this time due to this uncertainty. However, a SLGT risk upgrade may
be needed if signals continue to support another day of heavy rain
on Monday.
Weiss
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
314 PM EDT Sun Oct 4 2026
Day 3
Valid 12Z Tue Oct 06 2026 - 12Z Wed Oct 07 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF
FLORIDA AND SOUTHEAST GEORGIA...
20Z Update: Minimal changes necessary for the D3 time frame. Models
continue to signal isolated instances for flash flooding across
north-central FL, as well as the coastal areas between St.
Augustine down towards Port St. Lucie. Main concerns will be within
those urban centers where flash flooding over the impervious
surfaces creates the most issues historically. Ensembles across the
region north of I-4 are between 1.5-2.5" in the means with the
environment more than capable convective development due to the
convergence axis near the front and the general buoyancy thanks to
the lingering tropical airmass over the region.
Kleebauer
..Previous Discussion..
The cold front from Monday will stall across the northern Florida
Peninsula Tuesday as a stationary front. This front will meander
subtly north/south through D3, remaining entrenched within weak
mid-level flow and a plume of anomalous PWs progged to be over
2.25", or above the 97th climatological percentile according to
NAEFS. Weak mid-level shortwaves traversing slowly atop the
boundary will enhance ascent, and despite modest instability, the
overlap of sufficient ascent within the deep tropical moisture will
result in yet another day of heavy rain as convection trains WSW to
ENE on 0-6km mean winds parallel to the boundary. With rain rates
expected to reach 1-2"/hr, at least isolated flash flood impacts
are expected, especially where rain moves across areas that also
experience heavy rain on D2 /Monday./ Effective bulk shear of 20-30
kts may support some modest organization which could enhance the
risk to drive a targeted upgrade to a SLGT risk, but at this time
maintained the MRGL risk due to uncertainty in the intensity and
footprint.
Weiss
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
314 PM EDT Sun Oct 4 2026
Day 4 and Day 5
Valid 12Z Wed Oct 07 2026 - 12Z Fri Oct 09 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE GULF COAST & TEXAS BIG BEND...
A stationary surface front will remain draped roughly halfway
across the FL Peninsula Tuesday through Thursday and will continue
to be a focus for potentially heavy rainfall through at least
Wednesday night. The axis of highest PWs (2.25-2.5") and mid-
level shortwave energy will be be in the front's vicinity, as well
as instability from the nearby Gulf. Deep west/west- southwesterly
flow will enhanced the risk for training cells coming off the
eastern Gulf across central FL, while anti- parallel flow to the
front's north across northern FL bringing in instability from the
subtropical Atlantic and could lead to very high precipitation
efficiency. Effective bulk shear values over 20kts would allow for
some degree of organization on Wednesday. Hourly rainfall amounts
to 3" should be possible given the available ingredients. In the TX
Big Bend, enough moisture and instability could be present for an
isolated flash flood possibility, which led to a new Marginal Risk
area. Hourly rain amounts to 2" are possible given the available
ingredients there.
On Thursday/Thursday night, the guidance shows the front across FL
becoming broader as the subtropical ridge begins to build across
the FL Peninsula. Meanwhile, enough Gulf moisture/instability
flirts with portions of southeast LA, Padre Island TX, and the TX
Big Bend Thursday into Thursday night to lead to occasional heavy
rainfall signals in these areas. Changes were minimal to the
Wednesday/Wednesday night Marginal Risk area, mostly confined with
expansion near the eastern border of FL/GA. For Thursday/Thursday
night, Marginal Risks were added for southeast Louisiana, Padre
Island TX, and portions of the TX Big Bend. Much like the previous
day, hourly rain amounts to 3" are possible near sections of the
Gulf Coast given the available ingredients and 2" for portions of
the TX Big Bend.
Roth
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
314 PM EDT Sun Oct 4 2026
Day 4 and Day 5
Valid 12Z Wed Oct 07 2026 - 12Z Fri Oct 09 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE GULF COAST & TEXAS BIG BEND...
A stationary surface front will remain draped roughly halfway
across the FL Peninsula Tuesday through Thursday and will continue
to be a focus for potentially heavy rainfall through at least
Wednesday night. The axis of highest PWs (2.25-2.5") and mid-
level shortwave energy will be be in the front's vicinity, as well
as instability from the nearby Gulf. Deep west/west- southwesterly
flow will enhanced the risk for training cells coming off the
eastern Gulf across central FL, while anti- parallel flow to the
front's north across northern FL bringing in instability from the
subtropical Atlantic and could lead to very high precipitation
efficiency. Effective bulk shear values over 20kts would allow for
some degree of organization on Wednesday. Hourly rainfall amounts
to 3" should be possible given the available ingredients. In the TX
Big Bend, enough moisture and instability could be present for an
isolated flash flood possibility, which led to a new Marginal Risk
area. Hourly rain amounts to 2" are possible given the available
ingredients there.
On Thursday/Thursday night, the guidance shows the front across FL
becoming broader as the subtropical ridge begins to build across
the FL Peninsula. Meanwhile, enough Gulf moisture/instability
flirts with portions of southeast LA, Padre Island TX, and the TX
Big Bend Thursday into Thursday night to lead to occasional heavy
rainfall signals in these areas. Changes were minimal to the
Wednesday/Wednesday night Marginal Risk area, mostly confined with
expansion near the eastern border of FL/GA. For Thursday/Thursday
night, Marginal Risks were added for southeast Louisiana, Padre
Island TX, and portions of the TX Big Bend. Much like the previous
day, hourly rain amounts to 3" are possible near sections of the
Gulf Coast given the available ingredients and 2" for portions of
the TX Big Bend.
Roth
