FOUS30 KWBC 030740 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 340 AM EDT Sat Oct 3 2026 Day 1 Valid 12Z Sat Oct 03 2026 - 12Z Sun Oct 04 2026 ...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE CENTRAL GULF COAST AND THE LOWER TEXAS COAST... ...Central Gulf Coast... A tropical wave moving across the Gulf will funnel record to near record amounts of atmospheric moisture into much of the Gulf Coast on Saturday. A 15-25 kt southerly flow into the coast at 850 mb will support numerous showers and thunderstorms associated with the wave moving into the central Gulf Coast both today and tonight. PWATs will be at or above 2.5 inches for many areas. Extensive cloud cover and the October sun should limit instability considerably with any reasonable distance from the coast. Thus, any convection that impacts the coast is unlikely to be able to travel too far inland without significant weakening. Thus, the Slight highlighting much of the coast remains unchanged. A higher-end Slight Risk was added with this update from New Orleans through much of the western Florida Panhandle. They were primarily included due to urban impacts and the sheer volume of water expected, as the coast can expect 3-6 inches of rain today, with locally higher amounts. Despite very high FFGs and dry soils in this area, this amount of rainfall may overcome that, especially in urban areas to result in widely scattered instances of flash flooding. ...Lower Texas Coast... The Slight risk remains in place along the coast of Deep South Texas as well. Onshore northeasterly flow of the same deep tropical moisture impacting areas further north and east may impact some urban areas such as Brownsville. As this portion of the Lower Texas Coast is roughly perpendicular to the mean flow, expect the onshore push to allow convection to try to move a few miles inland before dissipating. No changes were made to the area included in the Slight Risk with this update. Wegman 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... 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. Only minor changes were needed, which included adding a bit more of the southern Outer Banks to the Slight, in coordination with MHX/Morehead City, NC forecast office. 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. Meanwhile across the Carolinas, the second consecutive day of rain, and for most areas, far more than on Saturday, should allow for more widely scattered instances of flash flooding, so the Slight Risk is largely unchanged and still looks on track. Portions of the South Carolina Low Country and Georgia coast were trimmed since sandy soils and swampy terrain should preclude any flash flooding, since the heaviest rains are likely to be north and west of this area. ...Lower Texas Coast... No changes were needed along the Lower Texas Coast, as continued onshore flow will continue the same pattern from Saturday. Some convection that develops over the Gulf will attempt to move ashore, then quickly die off due to a lack of instability further inland. Wegman 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... 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... An overall weakening of both the tropical wave over the Gulf and the subsequent easterly/onshore flow should limit additional rainfall along the immediate coast on Monday. Thus, despite several days of prior rains, the inherited Marginal was left in place with few changes. Wegman Day 4 and Day 5 Valid 12Z Tue Oct 06 2026 - 12Z Thu Oct 08 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL TUESDAY-TUESDAY NIGHT OVER FAR SOUTHEAST GEORGIA INTO NORTHERN AND CENTRAL PORTIONS OF THE FLORIDA PENINSULA... Day 4 (12Z Tue-12Z Wed) -- Little change made to yesterday's Day 5 Marginal Risk area. The Marginal area slips a little farther south into North-Central FL and far southeast GA Tue-Tue night, where the surface front more than likely will begin to stall and become quasi-stationary. The axis of highest PWs (2-2.5") and mid-level shortwave energy will be draped along and south of the front, as will some (albeit weak) deep-layer instability. Deep west/west- southwesterly flow will enhanced the risk for training cells coming off the eastern Gulf, as all the global ensembles (GEFS/ECENS/CMC) have at least a few members noting rainfall totals of 3-5+" within the 24hr period. However it should be noted the QPF (deterministic and probabilistic) trends in the guidance has decreased over the past couple of model cycles, with now the highest 3-5+ inch QPF probabilities over the waters of eastern Gulf and off the Atlantic Coast per the GEFS/ECENS/CMC (where deep-layer instability is more conducive). For now, we did not include another Marginal Risk in the Day 5 ERO (12Z Wed-12Z Thu) across Central FL. Yes the front will remain hung up in the vicinity, however the heavy rainfall signal is more diffuse with the 0-6km Bulk Shear values over 20kts along and north of the front, implying more anafrontal rainfall where the deep- layer instability (elevated) is marginal at best. Areal spread in the QPF among the global models is also rather high, again with the heavier amounts over the water (Gulf and Atlantic) where the instability is decidedly more favorable. Meanwhile, of late the AI guidance (both ECMWF AIFS and AIGFS QPF) have verified better of late, largely due to the AI models having a better handle on the frontal progression. By day 5, both the AIGFS and EC AIFS show the QPF axis a bit farther south (Central-South FL) compared to the rest of the guidance, and not nearly as heavy with the amounts compared to the latest NBM. Given the high FFG over this area, and the concern that the rates will not be sufficiently high given the lack of deep-layer instability, we opted to refrain from hoisting a Marginal Risk area. Hurley 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 $$