Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
829 PM EDT Sun Oct 4 2026
Day 1
Valid 01Z Mon Oct 05 2026 - 12Z Mon Oct 05 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE LOWER TEXAS COAST & SOUTHEAST...
...Lower Texas Coast...
While a small area of thunderstorms moving down the intracoastal
between is fading, other activity in the Gulf appears to be heading
into the region. Both the 12z REFS/18z HREF indicate heavy rain
potential overnight within a very moist air mass in an environment
where 500-2000 J/kg of ML CAPE remains present. There's not enough
of a signal for a Moderate Risk any longer, so downgraded the risk
to a Slight as a course of least regret. Hourly rain amounts to 3"
are possible overnight.
...Southeast U.S...
Due on ongoing convection across portions of southeast LA, AL, MS,
southern SC/adjacent GA, as well as an overnight/early Monday
morning uptick in convection expected near the Central Gulf Coast
within a regime of onshore flow, a Slight Risk remains across
portions of the Southeast. Coverage of all risk areas has been
pared back to account for recent radar reflectivity trends and
trends in the 12z REFS/HREF guidance. Hourly rain amounts to 3" are
possible within the moist and unstable air mass present, and
recent days of rain have partially saturated area soils, so still
believe a high-end Slight Risk is reasonable for far southeast LA
and portions of the FL Panhandle.
Roth
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
829 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: The 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
829 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
829 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
829 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
