305 FOUS30 KWBC 041551 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1151 AM EDT Sun Oct 4 2026 Day 1 Valid 16Z Sun Oct 04 2026 - 12Z Mon Oct 05 2026 ...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE LOWER TEXAS COAST... ...Lower Texas Coast... 16Z Update: Radar and satellite composite continue to point to an active morning and afternoon for areas of the lower Texas coastal plain to areas inland, down towards the lower RGV and the population centers. Recent trends have noted an uptick along the immediate TX coast in Kennedy county down towards northern Willacy leading to rainfall rates between 1.5-2"/hr at peak intensity. This continues to overlap areas that were hit flush overnight into the early morning hours leading to likely some flooded areas across the King Ranch domain. Radar estimates from the MRMS gauge corrected data source indicate an area of 3-6" has already fallen across the eastern portions of Kennedy county with a swath of 1-3" located south of the area. This trend will continue allowing for an elevated flood risk over the entire stretch from Kennedy county down into Brownsville with a western inflection towards McAllen and all areas in-between. Highest risk for flash flooding will continue to be those urban zones littered across Deep South TX, including the metro area between Brownsville-McAllen, as well as potential for places like Harlingen and Raymondville. HREF neighborhood probabilities for >5" of rainfall for the event continue to be elevated across Kennedy county down towards Port Mansfield, but there remains a sharp western edge to the threat with more modest probs for >2" and >3" available further back into those population centers. Maintained the MDT risk given the ongoing heavy rain signal across the region, but anticipating a slow degradation of the threat later this evening into the overnight hours with a bit more of a scattered heavy rain forecast for the region after 00z. For more on the current setup across the area with the ongoing heavy rain into the lower Texas coastal plains, please refer to MPD #1441. ...Southeast U.S... 16Z Update: Quasi-stationary front extending from the coast of TX into the southeastern U.S. will continue to slow press south as more stable air wedges down east of the Appalachian front creating a textbook damming signature across the Carolina Piedmont into northeastern GA. 12z surface analysis and regional observations indicate the frontal alignment through the SC Midlands extending into the vicinity of Augusta, GA and off to the northeast, extending just beyond North Myrtle Beach within the past few hours. This trend will continue leading to a sharp cutoff on the northern periphery of the better convective environment with the best threat for heavy rainfall located along and south of the front during its progression. Assessment of regional theta_E's tells a big story on the frontal positioning, along with the available instability for the deep layer moisture to tap into during traditional diurnal heat flux late-morning through the afternoon and evening hours. Current progs are for scattered convection with likely heavy rain cores stemming from the PWATs sufficiently above 2" across much of the Southeast U.S, mainly south of the front. Prevailing southerly flow around a ridge positioned over the FL Peninsula will serve as a mechanism for continued to moisture advection and sending some of these waves of mid-level energy out of the adjacent Gulf into the coastal plain LA over into the FL Panhandle. PWATs from the 12z sounding out of KLIX indicated climatologically anomalous moisture pooling over the immediate central Gulf Coast with values up around 2.5", a solid 95-99th percentile for the date and month, respectively. Coupled with the energy slowly advancing out of the Gulf and elevated instability located along and just over the nearby Gulf waters, cases of heavy rainfall have continued to plague areas from southeastern LA over into the western FL Panhandle. Multiple flash flood warnings were issued this morning over near Destin/Fort Walton Beach with a surge of heavy rainfall stemming from the advection regime off the Gulf. Current radar indicates a band of heavier rain impacting southeast LA into southern MS, a signal that has been prevalent from much of the CAMs this morning. Expectation is for this threat of locally heavy rainfall to continue through the afternoon and evening hours with scattered instances of flash flooding noteworthy for those urban areas along I-10 to the coast. Rainfall rates between 1-3"/hr are likely in any of these stronger convective cores thanks to the anomalous deep layer moisture with the 12z RAOB sounding indicating tropopause levels up towards 150mb, a signature normally seen with tropical airmass types. So long as we maintain persistence in this setup, there remains an elevated threat for flash flooding in this region of the CONUS, extending inland into southeast AL and southern GA over towards the SC/GA coastal plain. HREF EAS probabilities for >2" remains solidly above 20% from the bayous of southeast LA over into the corridor from Hilton Head, SC to near Jacksonville, FL. A general max prob is situated over the western FL Panhandle with a "bullseye" of 40-60% located between Pensacola to Panama City Beach. This is the area where the opportunity for more appreciable totals >4" for the event could spell multiple chances for flash flooding given the urban density factor. A broad SLGT extends from the coast of LA to FL/GA and points north into central AL/GA as the environment in this area remains favorable for heavy rain prospects as the front slowly makes its progression into the area over the course of the period and the eventual D2. A high-end SLGT remains forecast from Biloxi to Tallahassee with a northern bound centered over southeastern AL into southern GA to the GA coast. This is the area where heavy rainfall potential of 2+ inches per hour are most likely given the latest HREF hourly probabilities, enough to enhance flash flooding in any urban corridor in this region, as well as the clay hills of southern GA. Kleebauer 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... Another day of heavy rainfall is likely across the Lower Texas Coast and into parts of South Texas, likely increasing or exacerbating flash flooding impacts anticipated during D1. 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 5"/24hr probabilities above 50%). For this reason a SLGT risk has been added for a narrow corridor of the BRO CWA. ...Southeast... 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 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... 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 4 and Day 5 Valid 12Z Wed Oct 07 2026 - 12Z Fri Oct 09 2026 ...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL WEDNESDAY ACROSS PORTIONS OF THE FLORIDA PENINSULA... 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 (current Day 4). 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. However on Thursday, the guidance shows the front become a little more diffuse as the subtropical ridge and a more DNVA regime begins to build across the FL Peninsula. This would explain why the 00Z operational global QPFs (GFS/ECMWF/UKMet/CMC) are lower on Day 5 compared to Day 4. As a result, at least for now, we did not extend the Marginal Risk area into the Day 5 ERO. Hurley/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 $$