Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Oct 07 2024 15:29:48 FOUS30 KWBC 071529 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1129 AM EDT Mon Oct 7 2024 Day 1 Valid 16Z Mon Oct 07 2024 - 12Z Tue Oct 08 2024 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE SOUTH FLORIDA PENINSULA AND ALL OF THE FLORIDA KEYS... 16Z Update: Continued heavy rainfall prospects will plague South Florida through the period as surface low propagation and general placement will create an extensive period of primed sfc-925mb convergence within an area of PWAT anomalies around +3 standard deviations just based on the latest 12z sounding analysis out of KEY and MFL. Latest CAMs output was generally similar in its orientation of a band of heavy rainfall bisecting the Southern section of the FL Peninsula, but some discrepancy on specific placement of the axis of strongest convergence. Regardless of the differences in placement, there is enough consensus based off neighborhood probabilities for >5" (60-90+%) and >8" (35-60%), as well as EAS probabilities for >2" (50-80%) to adjust the previous=20 MDT risk, allowing for an expansion across all of the Southern FL=20 Peninsula between just north of Naples, across I-75 and points=20 south. The prospects for heavy rain in the FL Keys remains elevated with the highest probabilities bisecting the Upper Keys with a=20 southern inflection point in the highest probs generally north of=20 Islamorada and the Middle Keys. Despite the sharp cutoff within the CAMs, the environment is more than conducive for locally enhanced=20 rainfall off any well defined bands that drift out of the Gulf and=20 impact the Lower half of the Keys. In fact, the MUCAPE alignment=20 benefits the Lower and Middle Keys the most considering the current Mesoanalysis and forecast within the CAMs. The strongest signal=20 for both instability and low- level convergence is a bit further=20 north within that area encompassing I-75 and south.=20 In coordination with the local WFOs in Miami and Key West, the MDT was expanded to include those areas in the urban corridor along=20 both coasts and all of the Southern tip of the Peninsula. The MDT=20 was also expanded northward along the Southeast FL coast up to=20 Port St Lucie in WFO MLB CWA due to a prominent signal for locally=20 enhanced rainfall in- of the coastal plain due to a prolonged=20 frictional convergence pattern situated along the Southeastern FL=20 coast this afternoon. The threat was defined enough to expand the=20 higher risk to cover for the potential.=20 Kleebauer Day 2 Valid 12Z Tue Oct 08 2024 - 12Z Wed Oct 09 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE FLORIDA PENINSULA... There will be a general lull in the overall general rainfall across Florida on Tuesday. The "calm before the storm". The low impacting most of the state Monday will be well east of the Bahamas by Tuesday, while the rainfall directly associated with Hurricane Milton will likely remain off or just arriving at the Gulf Coast before 12Z Wednesday. Nevertheless, widespread light to moderate rainfall will impact the state Tuesday and Tuesday night. Thus, any resultant flooding will be largely due to favorable antecedent conditions due to generally widespread saturated soils across the Peninsula. Further, continued extremely moist atmospheric conditions consistent with the deep tropical air mass with PWATs around 2.25 inches will still support locally heavy rainfall with any convection that manages to form. On the Atlantic side, a convergence zone may remain over the Space and Treasure Coasts on Tuesday, which could locally organize any convection and result in locally heavier rainfall over these mostly urban areas. Meanwhile over the Gold Coast, a local minimum of rainfall may develop, but the heavy rain there the past couple days as well as some chance of shower and thunderstorm activity may cause widely scattered localized flooding. No changes were made to the ERO risk areas. Wegman Day 3 Valid 12Z Wed Oct 09 2024 - 12Z Thu Oct 10 2024 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR CENTRAL AND NORTH FLORIDA AS WELL AS FAR SOUTHEASTERN GEORGIA... The main circulation of Hurricane Milton will cross the Florida Peninsula on Wednesday. There remains considerable uncertainty as to where the center will make landfall, which will of course play a huge role as to where the heaviest rainfall amounts will be. See the NHC forecast for the latest track. The storm is expected to be undergoing increasing shear, beginning extratropical transition, growing in size, and ingesting dry air. Thus, there is decent agreement that at landfall, the storm will be weakening. This should help to reduce the rainfall south of the circulation center as dry air ingestion associated with extratropical transition should quickly erode the rain-producing storms southwest of the center. Very dry air behind a southward moving front will greatly cut into rainfall amounts on the northern fringe of the circulation. Thus, expect there to be a tight gradient of rainfall both on the south and north sides of the circulation, but for different reasons. The ERO risk areas have been expanded in both directions due to track and storm size uncertainties, especially towards the north, with the Moderate Risk expanded into far southeastern Georgia, and the surrounding Slight and Marginal expanded into the Low Country of coastal southern South Carolina. This may be optimistic, but these expansions were made primarily due to uncertainties, and will likely be refined in the coming days. For the moment, there are several reasons a High Risk was not considered in no particular order: 1) The storm will be weakening prior to landfall which may temper rainfall amounts a little bit, 2) Milton's small size should reduce the areal coverage of the heaviest rain, 3) The primary rain footprint of Milton over north Florida will largely miss where the hardest hit areas of the PRE in south Florida are. Of course there is some overlap, but not nearly as much as with Helene, 4) The core of the heaviest rain at the moment is expected to track from north of Tampa northeast through around Jacksonville. This area has been relatively dry in recent days compared to areas further south, 5) Milton will be moving quickly and accelerating. This will reduce the time the heaviest rain has along and north of the track to result in widespread and numerous flash floods, 6) The inclusion of CAMs and higher certainty with the track may help to narrow down where a potential High Risk may be needed with future forecasts. For now with Day 3 being outside the CAMs time range, the large Moderate will suffice. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!9hZSgx9UiXNUsp_CD0_tBkLcmRSFCK-LJgiK2iIEygl1= 98bwrXSdVTsJ_dnmjKtlXBiOIogJt7ijpUsfs_m7oAPzWS4$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!9hZSgx9UiXNUsp_CD0_tBkLcmRSFCK-LJgiK2iIEygl1= 98bwrXSdVTsJ_dnmjKtlXBiOIogJt7ijpUsfs_m7z6tjBYA$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!9hZSgx9UiXNUsp_CD0_tBkLcmRSFCK-LJgiK2iIEygl1= 98bwrXSdVTsJ_dnmjKtlXBiOIogJt7ijpUsfs_m75kPp_OI$=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .