Subj : MESO: Heavy rain/flooding To : All From : Mike Powell Date : Sat Sep 30 2023 08:11:00 AWUS01 KWNH 300932 FFGMPD FLZ000-301530- Mesoscale Precipitation Discussion 1117 NWS Weather Prediction Center College Park MD 530 AM EDT Sat Sep 30 2023 Areas affected...Portions of the FL Atlantic Coast Concerning...Heavy rainfall...Flash flooding possible Valid 300930Z - 301530Z SUMMARY...Slow-moving showers and thunderstorms this morning with locally extreme rainfall rates may produce some areas of flash flooding. DISCUSSION...The latest radar imagery has been showing an uptick in very heavy shower and thunderstorm activity around the Daytona Beach, FL area and extending offshore with some linear bands becoming aligned with a convergent low-level flow regime just north of a quasi-stationary frontal zone. A very moist and unstable airmass is pooled across the region with PWs that are running over 2 standard deviations above normal with values of 2.25 to 2.5 inches. The 00Z RA0B sounding from KXMR (Cape Canaveral) was reflective of a very deep and warm tropical column with WBZ heights well over 15,000 feet and a PW of 2.31 inches. The latest RAP analysis shows MLCAPE values of 1500+ J/kg along the coast and already indicative of a moderately unstable airmass. The combination of convergent low-level easterly flow, westerly shear aloft, and this very moist and unstable airmass will support slow-moving and locally anchored convective cells focusing along and adjacent to the coast that will be capable of extreme rainfall rates. Some rainfall rates with the more organized convective cells this morning will be capable of reaching 2 to 4 inches/hour and this will also be connected to the fact there that is such a deep and moist warm cloud layer. The 06Z HREF guidance suggests a threat for localized storm totals reaching or exceeding 5 inches where the storms become more focused, and at least in the short-term, areas near Daytona Beach will be most at risk for seeing these heavier totals. Going through the morning hours, some additional expansion of convection especially to the north along the coast may be possible. Very high FFG values will certainly mitigate any flash flood threat to an extent, but with such high rainfall rate potential this morning, some flash flooding will be possible and especially if any urban areas can get into the stronger convective cores. Orrison ATTN...WFO...JAX...MLB... ATTN...RFC...SERFC...NWC... LAT...LON 29878130 29828118 29598108 29228087 28808077 28598080 28678113 29008136 29428154 29758153 = = = --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .