FOUS30 KWBC 051559 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1159 AM EDT Mon Oct 5 2026 Day 1 Valid 16Z 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... 16Z Update: In coordination with local Brownsville WFO and in regards to the latest radar and short term trends in guidance, the SLGT risk was removed and replaced with a small MRGL to account for an isolated flash flood threat near and east of the Brownsville. HREF neighborhood probs for >3" on the latest 12z output continues to show a relatively modest threat for locally heavy rainfall near and just east of Brownsville proper. Heaviest rain has mainly been confined to South Padre Island and the southern most tip of TX leading to lower end threats for flash flooding. Recent CAMs indicate the best potential holding between now and just before the end of the afternoon before fading as the best convergent area and instability will align just off the coast for the overnight period. A few cells may try to sneak in off the nearby Gulf waters, but the prospects decrease just based on the hourly probabilities for >1"/hr. The SLGT risk was downgraded to just a MRGL risk, restricted to mainly eastern Cameron county and coastal Willacy. Kleebauer ...Southeast... 16Z Update: Our cold front is making a bit more of a steady southern progression this morning with the 12z surface analysis depicting the front right along the FL/GA border with an expectation for the front to bisect northern FL by later this afternoon. The threat is dwindling for the northern extent of the previous MRGL risk with the best chances for any locally heavy rainfall occurring now into the early afternoon hours over southern and eastern GA back into southern AL before ceasing by the evening. Best signature for heavy rainfall and totals between 2-4" will reside over the FL Panhandle between Destin to the Big Bend and up through the interior, near and west of Tallahassee. HREF and REFS EAS signatures for >2" are highest within that zone encompassing the Apalachicola Forest and the coastal towns along US98, an area that is traditionally hard to flood due to the sandier soils and the necessity for fairly elevated rates >3"/hr, outside a few towns like Panama City Beach and Apalachicola proper. The threat in those areas remains lower end given the setup and the greatest ascent lifting out of the region through the course of the afternoon. Some indications that convection off the nearby Gulf this evening can send an outflow or two towards land and create a localized area of enhanced rainfall along the immediate coast. This signature is hit or miss within the CAMs, but the threat is certainly non-zero for something like this to occur. PWATs between 2.3-2.5" reside in this area ahead of the cold front, so the environment is ripe for more efficient warm rain processes and potential for locally >2"/hr. In this case, the MRGL for the Panhandle area is more than sufficient. Further east, frictional convergence along the front between Savannah down through Jacksonville to St.Augustine will lead to isolated flash flood concerns along the I-95 corridor as the environment remains ripe with PWATs on the 12z KJAX sounding up at 2.44" this morning with a textbook tall, skinny CAPE signature that correlates positively to heavy rain prospects. HREF and REFS neighborhood probs for >5" are between 40-60% for that coastal area between GA/FL but low EAS probabilities for >2" signal the threat to be more isolated to widely scattered with the best risk tied to those urban zones due to higher run off potential. Some convection along the sea breeze further inland is also plausible with rates between 2-3"/hr at peak intensity, but considering the pulse nature of the convection, storms will have limited time before dwindling in intensity, thus only generating short windows of opportunity to promote flash flooding. The MRGL risk exists over northern and central FL into eastern GA given all of the above. Kleebauer 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 $$