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Flash Flood Guidance
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Issued by NWS
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797 AWUS01 KWNH 140921 FFGMPD FLZ000-141520- Mesoscale Precipitation Discussion 0435 NWS Weather Prediction Center College Park MD 520 AM EDT Fri Jun 14 2024 Areas affected...southern FL Concerning...Heavy rainfall...Flash flooding possible Valid 140920Z - 141520Z SUMMARY...Showers and thunderstorms are expected to increase through 12Z across southern FL. Areas of training may support high rainfall rates of 2 to 3+ in/hr, renewing flash flood concerns over the region. DISCUSSION...GOES East 6.9 micron imagery showed a subtle shortwave crossing the southern FL Peninsula at 0845Z, located to the southeast of a mid to upper-level trough axis that extended across northern FL into the central Gulf of Mexico. Radar and infrared satellite imagery has shown an uptick in mostly warm topped shower activity over the past hour from near the Dry Tortugas to the southwestern coast of the FL Peninsula where SPC mesoanalysis data showed 500-1000 J/kg MLCAPE with decreasing convective inhibition through 08Z along with precipitable water values between 2.0 and 2.4 inches. Layered PW imagery showed a similar setup to 24 hours ago in the low levels with an elongated cyclonic circulation (~850 mb) near and northeast of 30N 80W, with a southwestward trailing axis of convergence extending ENE to WSW across the FL Peninsula to the south of Lake Okeechobee. Aloft, there is a notable difference compared to yesterday which is the approach of the positively tilted mid to upper-level trough axis over the Gulf with modestly diffluent and divergent upper level flow over far southern FL. Over the next 3 to 6 hours, increasing low level confluence focused within the 925-850 mb layer is expected to set up to the southwest of and across southern FL as southerly flow across the Keys meets with veering flow to the north in the wake of the subtle shortwave impulse. Mean southwesterly steering flow will likely support some localized training with the expected increase in cell coverage. With existing CIN eroding from south to north across the Everglades, the available moisture and instability is expected to support efficient rainfall production with hourly or subhourly rainfall of 2 to 3+ inches near and south of the elongated low level convergence axis extending across southern Peninsula. Soils are still saturated throughout many areas of the region due to extreme rainfall over the past 2-3 days of 15 to 25 inches. While the coverage of additional heavy rainfall remains uncertain, the expectation for increasing shower/thunderstorm coverage and high rainfall rates warrants concern for renewed areas of flash flooding heading through the remainder of the morning hours for southern FL, including the Keys. Otto ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...KEY...MFL... ATTN...RFC...SERFC...NWC... LAT...LON 26808016 26757984 26357976 25747979 24718045 24308166 24408205 24748209 25108204 25708193 26198202 26328145 26638069