Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Oct 07 2024 20:10:43 FOUS30 KWBC 072009 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 409 PM 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 MDT risk, allowing for an expansion across all of the Southern FL Peninsula between just north of Naples, across I-75 and points south. The prospects for heavy rain in the FL Keys remains elevated with the highest probabilities bisecting the Upper Keys with a southern inflection point in the highest probs generally north of Islamorada and the Middle Keys. Despite the sharp cutoff within the CAMs, the environment is more than conducive for locally enhanced rainfall off any well defined bands that drift out of the Gulf and impact the Lower half of the Keys. In fact, the MUCAPE alignment benefits the Lower and Middle Keys the most considering the current Mesoanalysis and forecast within the CAMs. The strongest signal for both instability and low- level convergence is a bit further north within that area encompassing I-75 and south. In coordination with the local WFOs in Miami and Key West, the MDT was expanded to include those areas in the urban corridor along both coasts and all of the Southern tip of the Peninsula. The MDT was also expanded northward along the Southeast FL coast up to Port St Lucie in WFO MLB CWA due to a prominent signal for locally enhanced rainfall in- of the coastal plain due to a prolonged frictional convergence pattern situated along the Southeastern FL coast this afternoon. The threat was defined enough to expand the higher risk to cover for the potential. 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... 20Z Update: Little to no change was necessary for the previous ERO forecast as guidance remained steadfast on a D2 minimum for QPF post-surface low impact and prior to the impacts of Milton. Highest potential for flash flood concerns will align with the convergence axis south of MLB with secondary convergence axis positioned over Daytona. The Southwestern FL coast has the highest neighborhood probabilities for >3" (45-60%) with the highest located over Fort Meyers and Naples, an area that will be running above the 90th percentile in terms of soil moisture anomalies as indicated by the latest NASA SPoRT output.=20 Kleebauer ...Previous Discussion.. 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... 20Z Update: Hurricane Milton will continue progressing northeast through the Eastern Gulf with a modest increase in forward propagation. The storm is also forecast to undergo some weakening given the increasing 850-250mb shear axis as it approaches the FL Mainland, but will also be increasing in size due to a profound synoptic pattern to the northeast providing right-entrance region dynamics within a 150-160kt jet streak. The entire combination will cause the tropical cyclone to begin the initial stages of extra- tropical transition with a shift in the precip orientation more to the northern periphery of the cyclone, but still a fairly significant rainfall footprint trending through the northern half of the FL Peninsula (5-10" with locally higher). The previous=20 forecast was generally maintained especially within the confines of the MDT risk, however there was a noted sharpening of the northern precip gradient, something that has been trending sharper as we=20 move closer as guidance begins resolving the positioning of the=20 quasi- stationary front to the north of Milton that will provide a=20 delineation marker for the northern most extent of the tropical=20 moisture flux. The risk areas across GA were trimmed back into FL=20 with only the far Southeast corner of the state within the JAX CWA=20 maintained in the MDT as signals are still prominent for heavy rain and flash flood concerns regarding the St. Johns River basin the=20 latter part of the forecast period, heading into D4.=20 There is still some uncertainty regarding the exact track of Milton on Wednesday afternoon and beyond, but consensus within the recent ensemble and hurricane model suite is leaning more towards a Tampa and just north for the immediate landfall, a track that would offer the heaviest rainfall from Sarasota/Bradenton and points north aligning with the current MDT risk forecast. The forward speed of Milton will also play a significant role in the upper percentile for QPF outputs with a slower storm likely to involve greater fresh water flooding concerns across the Central and Northern Peninsula. There has been a minor trend in a slightly slower solution compared to previous forecasts, however the storm is still above the mean motion historically for Gulf hurricanes, so the prospects for a High Risk remain noteworthy, but still constitutes more monitoring on the forward speed as the correlation for flash flood concerns is markedly high, namely for the immediate Gulf coast and the FL=20 Peninsula. Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7J8PHshzogFDjnIsmqwtPvfI3OYRPz6Y7x-CqJQAQef1= 4209-afs82wDEbcortdqeKWy01NCb_n-lHCWRMfU2_Xf0Xc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7J8PHshzogFDjnIsmqwtPvfI3OYRPz6Y7x-CqJQAQef1= 4209-afs82wDEbcortdqeKWy01NCb_n-lHCWRMfUEPORaTc$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7J8PHshzogFDjnIsmqwtPvfI3OYRPz6Y7x-CqJQAQef1= 4209-afs82wDEbcortdqeKWy01NCb_n-lHCWRMfUBBxvzeo$=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) .