Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Nov 16 2023 08:09:06 FOUS30 KWBC 160809 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 308 AM EST Thu Nov 16 2023 Day 1 Valid 12Z Thu Nov 16 2023 - 12Z Fri Nov 17 2023 ....THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF THE EASTERN FLORIDA COAST... Dual surface lows are currently situated over both the central Gulf and tucked into the southern FL Peninsula. Deep, moist conveyor is positioned right over the northern Keys into the southern tip of the FL Mainland with rainfall rates exceeding 2"/hr within the heaviest band. Surface low and associated upper-level vorticity progression will play a key role in the potential for heavy rainfall today. The morning will see a lingering heavy rain threat across south FL with the best axis of precip located near and north of the Miami Metro, closer to Fort Lauderdale. This will advance slowly to the northeast and eventually off the coast prior to 18z, but the threat of locally heavy rain and flash flooding concerns will continue until that precip axis pulls away. Considering the antecedent conditions present from the copious amounts of rainfall near Fort Lauderdale up into Pompano Beach the past 36 hrs, the threat for flood impacts will linger leading to continuity in the SLGT risk placement overhead. Further north, locally heavy rain will be possible with the northern extent of the deformation precip field as the surface low scoots northeast up the FL coast, but the best risk for locally heavy rainfall will occur later in the afternoon and evening when we see the 5H pattern evolve overhead as our shortwave trough and attendant vorticity couplet shove eastward. This is where the forecast gets a bit tricky on the exact placement of an expected heavy rain band that will be the result an energy transfer from the shortwave over the Gulf to the wave off the FL coast. Where the mid-level vort maxes meet over the Peninsula, that's where the best ascent will be focused, seen very well within the 5H and 7H VV fields. The timing of this occurrence is trending towards mid-late afternoon and carrying through the early evening hrs as we have consensus on mid and upper level progression. The placement of the convergence is the tricky part with deterministic guidance wavering between an area from Port St. Lucie up through Daytona Beach as the prime location for the convective band to develop and pivot overhead. Considering the axis of 2 standard deviation above normal PWATs located within the confines of the area outlined, locally heavy rainfall on the scale of 2-3"/hr are within reason as reflected within the 00z HREF probability forecast (30-40% average between the two rate fields). Rainfall totals of 2-4" will be common along the immediate coast for the entirety of the D1 period within the Space Coast region, but the threat for a local maximum of up to 8" is not out of the question as indicated by both deterministic output and HREF probabilities (45-50% neighborhood probability of 8" near Melbourne as of the latest update). Given the localized threat and marginal uncertainty in the exact placement of the heavy convective banding along the FL coast, have opted to maintain the SLGT risk in place over much of the eastern FL coast, however the threat for higher localized impact will remain within the confines of the forecasted SLGT. The setup is also close to being a miss as well as a further eastward transfer would lead to the best convective enhancement tucking just off the coast, another reason to forego any upgrade despite the signal for an impactful event within the area outlined. Kleebauer Day 2 Valid 12Z Fri Nov 17 2023 - 12Z Sat Nov 18 2023 The probability of rainfall exceeding flash flood guidance is less than 5 percent. Kleebauer Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!7MKJwUggUF7hH-4pVqvxKcEUOTZP5UV4LfddS5rS-nKS= rmdHWNcFyAPTicJyws3sCBf2xDnjQFEkX-lbY90AFnHBOhc$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!7MKJwUggUF7hH-4pVqvxKcEUOTZP5UV4LfddS5rS-nKS= rmdHWNcFyAPTicJyws3sCBf2xDnjQFEkX-lbY90Aa80QzqI$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!7MKJwUggUF7hH-4pVqvxKcEUOTZP5UV4LfddS5rS-nKS= rmdHWNcFyAPTicJyws3sCBf2xDnjQFEkX-lbY90AEZBmoi0$=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .