FOUS30 KWBC 040037 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 837 PM EDT Sat Oct 3 2026 Day 1 Valid 01Z Sun Oct 04 2026 - 12Z Sun Oct 04 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE CENTRAL GULF COAST, THE LOWER TEXAS COAST, AND EASTERN NORTH CAROLINA... ...Gulf Coast... A inverted surface trough with an embedded cyclone moving across the western Gulf towards South TX will continue to funnel high moisture into much of the Gulf Coast into early Sunday morning. RAP guidance has tried to advertise another low-level circulation forming offshore southeast Louisiana that approaches at area at 06z or so, which should be watched. PWATs will be at or above 2.5 inches for many areas. Overnight, onshore flow should continue a stream of instability off the Gulf while disturbances aloft move by to the north. Only cosmetic changes were made to the inherited Slight Risk, mostly bridging the two separate areas together. A higher-end Slight Risk remains from southeast LA into the western Florida Panhandle. They were primarily included due to urban impacts and the sheer volume of water expected, as the coast has the potential for 3-6" of rain, with as much as 3" in an hour. Despite very high FFGs and dry soils in this area, this amount of rainfall may overcome that, especially in urban areas to result in at least widely scattered instances of flash flooding. ...In and near northern SC... The combination of an approaching front, 500-1500 J/kg of ML CAPE, and significant deep layer moisture has generated pockets of heavy rainfall, as of late across northern SC. Hourly rain amounts up to 3" have been indicated by 88D estimates. Recent trends within the 18z HREF/12z REFS indicate enough of a signal to move the Slight Risk westward to this area. Storms have not been quick to move thus far, and are expected to persist beyond 06z. Roth Day 2 Valid 12Z Sun Oct 04 2026 - 12Z Mon Oct 05 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHEAST AND LOWER TEXAS COAST... ...Southeast... 20Z Update: Changes for the D2 SLGT were minimal across Gulf coast and portions of the Southeast with an area of very heavy rainfall likely occurring along the immediate Central Gulf coast into the FL Panhandle. The SLGT risk further north was scaled back, however, as the trends on the latest guidance were for a more progressive push of the cold front and wedging stable airmass into the Piedmont of the Carolinas and Virginia. This has led to the heaviest precipitation threat located further south with the eastern periphery of the better forcing and moisture pushing offshore for eastern NC which would end a more appreciable threat. The general synoptic pattern remains favorable for continued onshore flow and frictional convergence along the coastal plain with ample buoyancy and well- above normal PWATs integrated across the Southeast. Cold front to the north will slowly press southward leading to enhanced convergence away from the immediate coast with a mid-level steering pattern influencing the moisture advection scheme with the deep moisture layer moving inland and then pivoting to the northeast through southern AL, central and southern GA, into the northern half of FL. Models are in agreement on a widespread 1-3" inland of the immediate coast, with locally higher totals embedded within the mean QPF distribution, positioned across southern and eastern GA into the FL Panhandle. The area situated between Mobile to Tallahassee continues to be the most prominent area of heavy rainfall with convective threats abound for much of the D2 thanks to a lingering surface wave progged to move into the general vicinity of the above area and maintain a prolonged axis of heavy rain within the eastern confines of the circulation. HREFpmm output of 5-8" remains consistent from the previous runs of the ensemble, leaving a good agreement on the prospects of at least scattered flash flooding within that area of the I-10 corridor to just inland. The high-end SLGT risk was maintained as a result of the continuity in the expected evolution of the synoptic forecast and coupled results in the precip distribution. A non-zero threat for an upgrade in the area of the Central Gulf coast remains, but an upgrade may be contingent on what transpires in the D1. We will be monitoring closely on the threat as it evolves the next 24hrs. Kleebauer ..Previous Discussion.. The combination of the continued funneling of record to near- record atmospheric moisture across the Southeast from a tropical wave over the Gulf, and an approaching cold front will allow for a swath of heavy rainfall to expand from the Central Gulf Coast northeast to portions of the Carolina coast. PWATs will range from 2.25 to 2.5 inches, which with good instability would be ample moisture to produce areas of significant flash flooding. However, the October sun and extensive cloud cover will instead limit instability significantly, with most areas struggling to reach even 1,000 J/kg of MUCAPE. Thus, this is likely to end up being a long- duration highly-efficient rainfall across the Slight Risk area. The Slight was also expanded north a bit to include the Birmingham, AL and Atlanta metros. Both of those cities will be on the northern edge of the rainfall plume, so there's considerable uncertainty given recent southward trends in the guidance as to the extent of any flash flooding. The urban nature of the area will be countered by weak instability. Once again the heaviest rains on Sunday will be in many of the same areas hit hard on Saturday, with perhaps a slight eastward shift from Saturday. Areas from Mobile, AL east across most of the Florida Panhandle are likely to see the most rain. Since there is significant overlap from Saturday, another higher-end Slight was introduced for this region. There is a non-zero chance, depending on how extensive any flash flooding from the rains today are, that a Moderate Risk upgrade may be needed for Sunday. ...Lower Texas Coast... 20Z Update: SLGT risk was maintained across the immediate South TX coastal plain with the best threat likely over the King Ranch area down towards South Padre Island and areas just inland of the coast. HREF neighborhood probability for >5" remains elevated (50-80%) centered over Kennedy and Willacy counties, sneaking into the northeastern portion of Cameron. This area can take a lot of rainfall overall thanks to the sandier soil composition, however, the threat for 5+ inches of rainfall does leave the door open for scattered flash flood prospects as we monitor any potential the heavier rain can sneak into the more urbanized areas centered along the lower RGV. A high-end SLGT or further upgrade may be necessary pending the impacts from the previous period of rainfall. Kleebauer Day 3 Valid 12Z Mon Oct 05 2026 - 12Z Tue Oct 06 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHEAST AND LOWER TEXAS COAST... ...Southeast... 20Z Update: The cold front will continue to moving to the south with eyes on the Gulf coast into FL by the D3 period. Pending the positioning of the boundary, a SLGT risk may be necessary across portions of the FL Panhandle as noted via some of the ensemble members and bias corrected QPF outputs. There's discrepancy in the latitudinal push of the cold front and that will be play a big role in the alignment and placement of the heaviest rainfall. Global deterministic outputs were all over the place with some maintaining a less than enthusiastic signature on the prospects, to others putting a significant amount of rainfall in areas of southern GA and northern FL, overlapping some of the expected areas of impact from periods prior. This time frame is subject to adjustments of the MRGL risk in place, as well as potential upgrades pending the trends in guidance. The overall environment is more than capable of producing locally significant rainfall, but where it falls in this area of the CONUS is important, so it will be a period to monitor for any enhancements to the threat. Kleebauer ..Previous Discussion.. Very few changes were needed with this update across the Southeast. While the trends in the guidance continue to suggest a southward trend, given the heavier rains from Sunday, the ERO remains generous on the northern side of the rainfall footprint, to account for potential ongoing flooding continuing into Monday. The heaviest rains on Monday will focus in far southeastern Georgia and from Jacksonville north and west in Florida. As on previous days, instability will be at a premium due to extensive cloud cover from the extremely high moisture amounts in the atmosphere. Much of the Florida Peninsula will have PWATs at or above 2.25 inches, supporting highly efficient warm rain processes. This will be countered by the lack of instability, which will limit the lift any storms will have to work with. By Monday, a somewhat faster southward movement of the cold front lifting all this moisture should significantly limit overlap in the forecast rainfall footprints from Sunday to Monday. Given how difficult most of southeast Georgia can be to flood due to flat, sandy terrain and numerous swamps, a high-end Marginal remains in place. A continued southward trend in the front could allow for trimming on the northern end of the Marginal with future updates. ...Lower Texas Coast... 20Z Update: No changes necessary to the previous forecast as the expected synoptic evolution remains consistent in-of the western Gulf into South TX. The threat for heavy rainfall will subside into Monday with the threat weakening as we step forward in the D3. Great chance for flash flooding will occur the first half of the D3 time frame (Monday AM through the afternoon), weakening as we head into Monday evening into Tuesday morning. Additional rainfall of 1-3" is forecast over the immediate South TX coastal plain extending inland towards areas like McAllen and Brownsville. The MRGL risk was maintained as a result. Kleebauer Day 4 and Day 5 Valid 12Z Tue Oct 06 2026 - 12Z Thu Oct 08 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL TOWARDS MIDWEEK IN AND NEAR FLORIDA... A stationary surface front is expected to be the focus for heavy rainfall Tuesday into late Wednesday in and near Florida. 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 could allow for some degree of organization. Hourly rain amounts to 3" with local totals to 6" are possible, given the expected ingredients available. Despite greater dispersion in the guidance Wednesday when compared to Tuesday, opted to include a Marginal Risk due to the possible impact. Roth Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt $$