Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Oct 06 2024 15:59:47 FOUS30 KWBC 061559 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 1159 AM EDT Sun Oct 6 2024 Day 1 Valid 16Z Sun Oct 06 2024 - 12Z Mon Oct 07 2024 ....THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR THE MIAMI- FORT LAUDERDALE METRO... 16Z Update.... Moderate Risk is maintained over the Miami metro area. Slight Risk is expanded up the length of the Florida Atlantic coast per coordination with WFOs MLB and JAX. A weak surface low remains west of the FL Peninsula morning. This=20 is well east of T.S. Milton, but in the same plume of incredibly=20 deep tropical moisture and will enhance southerly flow south of FL and easterly flow east of the Miami metro. PWATs are around 2.5" just southwest of the lower FL Peninsula to 2.1" near Palm Beach which has allowed heavy rains to develop and repeat on the southern side of the Miami metro and many areas of heavy rain looming just off the southwest FL Peninsula coast.=20 MPD 1091 has further info for southern FL. Portions of the Ft. Lauderdale and Miami metros saw up to 3 inches of rain on Saturday, further increasing risks to this urban corridor. Farther north up the FL Atlantic coast, convergence continues, but with lesser forcing than farther south. Enough confidence in scattered flash flooding through this afternoon to warrant=20 expanding the Slight Risk up the FL Atlantic coast into the GA=20 coast. All of south Florida gets heavy rains with 12Z HREF and recent HRRRs heavier south from Lake Okeechobee, warranting expansion of the Slight Risk there. The looming activity off the southwest FL coast should drift north. The 12Z CAM consensus (and subsequent HRRRs) is to keep it south of Tampa Bay, but the Slight Risk is maintained there with just a trim over northern suburbs given the regional radar depiction.=20 Jackson Day 2 Valid 12Z Mon Oct 07 2024 - 12Z Tue Oct 08 2024 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE SOUTHERN FLORIDA PENINSULA AND THE KEYS... The weak surface low that will bring heavy rain to south Florida on Sunday will continue eastward over the Peninsula and into the Bahamas by Monday afternoon. Heavy rain will likely continue over the southern Peninsula through at least Monday morning. There is considerable disagreement on the track, strength and the speed of the low, which will play a major role in how long the heavy rain persists into Monday afternoon. With somewhat better agreement that rainfall amounts will at least be lower than on Sunday, the Slight risk for the area that was inherited was largely maintained, albeit including some of the interior of the Peninsula as soils become saturated area-wide, resulting in close to 100% conversion of heavy rain to runoff. An internal higher-end Slight is in place for the Gold Coast, for the potential that should amounts from Sunday verify, then another targeted Moderate Risk upgrade will be necessary. Meanwhile, a second day of very heavy rain and thunderstorms is expected to impact all of the Keys, which at high tide times may cause flooding due to poor drainage. With some of the other CAMs moving the low across the southern Peninsula and east to the Bahamas, portions of the Gulf Coast, especially north of Ft. Myers/Cape Coral up through Tampa are in the rare decreasing trend in the forecast rainfall amounts on Monday. Thus, the Slight that extended up through Tampa was downgraded to a Marginal north of Ft. Myers/Cape Coral with this update. Wegman Day 3 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... The PRE (predecessor rain event) will enter its third and final day over the Florida Peninsula on Tuesday. The trough that occasionally spins up weak surface lows will remain in place across the Peninsula. The circulation of what will then be Hurricane Milton will make its approach to the Gulf Coast of Florida, likely near Tampa very late Tuesday night/early Wednesday morning. At this time, expect little of the rainfall directly associated with Milton's core to yet impact the Florida Peninsula. Of course, with future updates and forecast changes from NHC, this may change. Given the inherent uncertainty with the track and speed of this small hurricane, the Slight over the Peninsula was maintained, albeit with some filling in in the middle of the Peninsula near the Orlando area. There remains a bimodal distribution of the rain with much more expected along the Gulf coast from Tampa down through Naples, but with a secondary maximum for the Space and First Coasts. With the latest guidance, there is some offset of the axis of heaviest rainfall ahead of Milton. The northward trend will reduce amounts in portions of the hard-hit Gold Coast in favor of more rain for the northern Peninsula towards the First Coast. By Tuesday the greatest overlap will be over the Gulf Coast. It is here than an internal higher-end Slight was introduced for the Tampa through Naples area due to increasing amounts of heavy rain moving into the coast, being moved along by the predominant southwesterly flow in the trough ahead of Milton's core circulation. Heavy rainfall both the past couple days as well as expected both today and Tuesday should keep all of the soils on the Florida Peninsula at or near saturation, resulting in nearly all of the rainfall converting to runoff. Thus, progressively less rainfall will be needed to result in flooding. Despite Milton and directly associated rains largely holding to the Day 4/Wednesday period, it appears that similar to Helene, most of the rain over the Florida Peninsula will be associated with the PRE, while the heaviest rain (as well as wind and storm surge) will conclude the multi-day rain event with Milton moving through, causing much more widespread flooding. Wegman Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!_XniBObSRja7Jn2poS_AOIpPBGIjWzm3DHyfJ8XQrstu= pAdDT2wv4GAZpQ84dHotl7pO2xBTJFeZvhSUMA20_JXgjcc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!_XniBObSRja7Jn2poS_AOIpPBGIjWzm3DHyfJ8XQrstu= pAdDT2wv4GAZpQ84dHotl7pO2xBTJFeZvhSUMA205gazktE$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!_XniBObSRja7Jn2poS_AOIpPBGIjWzm3DHyfJ8XQrstu= pAdDT2wv4GAZpQ84dHotl7pO2xBTJFeZvhSUMA20mLFmQRo$=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) .