Flash Flood Guidance
Issued by NWS
Issued by NWS
358 AWUS01 KWNH 132051 FFGMPD FLZ000-140200- Mesoscale Precipitation Discussion 0432 NWS Weather Prediction Center College Park MD 450 PM EDT Thu Jun 13 2024 Areas affected...South Florida and the Florida Keys Concerning...Heavy rainfall...Flash flooding likely Valid 132050Z - 140200Z SUMMARY...A significant and locally life-threatening concern for flash flooding will continue across South Florida going into the evening hours as slow-moving showers and thunderstorms with extreme rainfall rates gradually cross the region. DISCUSSION...The latest GOES-E IR satellite imagery coupled with dual-pol radar shows an elongated band of deep convection with extremely heavy rainfall rates once again gradually settling southeastward across southern Florida. The coldest cloud tops within the convective band are still generally offshore over the southeast Gulf of Mexico where the stronger instability and moisture convergence has been focused, but some convective tops to about -65C have been occasionally occurring with the stronger convective cells that are seen crossing through the Florida Everglades, and also where MRMS data has been showing some rainfall rates of 1 to 3 inches/hour over the last couple of hours. MLCAPE values over southern Florida have risen to 1500 to 2500 J/kg, with a convergent southwest low-level jet of 20 to 30 kts in place. This is evidenced by the special 18Z MFL RAOB which also showed a PW of 2.41 inches and a very deep warm/moist column with the WBZ level up near 550mb or about 510 dm in height. The thermodynamic environment through the vertical column over southern Florida is highly conducive for extreme rainfall rates given the depth of tropical moisture and degree of instability, and the convective band settling southeast over the next few hours will be capable of producing 1 to 3 inch/hour rates, with isolated heavier rates perhaps to around 4 inches/hour with the strongest of cells. This is supported by the 12Z HREF guidance. Additional rainfall totals over the next few hours are expected to reach 4 to 6 inches with isolated heavier amounts not out of the question as the approaching convective band crosses the region, including the I-95 urban corridor from Boca Raton and Fort Lauderdale down through Miami. The convection will also gradually make it into far southeast Florida (i.e. Homestead) and into the Florida Keys by mid-evening impacting places such as Marathon and Key West with similar rainfall amounts expected. This evening`s axis of heavy rainfall overall should tend to be a bit more progressive compared to yesterday`s extreme rainfall event, but given such high sensitivities on the ground and lingering impacts from multiple days of extreme rainfall with multi-day totals over southern Florida locally of 15 to 25 inches, the additional rains heading through early this evening are very likely to exacerbate ongoing flooding/runoff problems and promote additional significant urban flash flooding concerns. Orrison ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...KEY...MFL... ATTN...RFC...SERFC...NWC... LAT...LON 26548048 26477996 25548009 24738069 24388171 24558205 24868132 25048120 25218119 25538124 25738135 25938128 26258097