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 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 $$