Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Oct 08 2024 00:56:14 FOUS30 KWBC 080055 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 855 PM EDT Mon Oct 7 2024 Day 1 Valid 01Z Tue Oct 08 2024 - 12Z Tue Oct 08 2024 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER FAR SOUTHERN FLORIDA INTO THE MIDDLE AND UPPER FLORIDA KEYS... A front draped across far southern FL into the Keys will be a focus for heavy rainfall through the overnight hours. A weak area of low pressure has developed off the east coast of FL, and northerly=20 flow behind this is likely helping push the front a bit further=20 southward. Convergence along this boundary is forecast to increase overnight which may allow for training convection and possible=20 flash flooding.=20 Given the further south front and instability gradient, we were=20 able to trim back the northern extent of both the Slight and MDT=20 risks with this update. The MDT risk is now confined to far south=20 FL into the middle and upper Keys. Recent HRRR runs have been very=20 persistent in indicating a corridor of training convection and as=20 much as 5-10" of rain on a localized basis. Totals of this=20 magnitude may be a bit high and still some uncertainty regarding=20 how robust and organized convection will get overnight. So while=20 the HRRR may be overdone, the ingredients near the boundary do=20 favor the potential for heavy rainfall if convection is able to=20 grow in scale tonight. Will need to continue to monitor radar and=20 satellite trends. Chenard 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. 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 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 move closer as guidance begins resolving the positioning of the quasi- stationary front to the north of Milton that will provide a delineation marker for the northern most extent of the tropical moisture flux. The risk areas across GA were trimmed back into FL with only the far Southeast corner of the state within the JAX CWA maintained in the MDT as signals are still prominent for heavy rain and flash flood concerns regarding the St. Johns River basin the latter part of the forecast period, heading into D4. 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 Peninsula. Kleebauer Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7TESzbYKtgfV3O_l20xXNtSXvkWi9Vgy-tL3a09MVyg5= qcRrb5X8HSfoI2eesVOaSmG_TwRdxAyqcpLpQz2m081Kw6w$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7TESzbYKtgfV3O_l20xXNtSXvkWi9Vgy-tL3a09MVyg5= qcRrb5X8HSfoI2eesVOaSmG_TwRdxAyqcpLpQz2mWizvqWk$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7TESzbYKtgfV3O_l20xXNtSXvkWi9Vgy-tL3a09MVyg5= qcRrb5X8HSfoI2eesVOaSmG_TwRdxAyqcpLpQz2m8Jt9ypQ$=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) .