Area Forecast Discussion
Issued by NWS Miami, FL
Issued by NWS Miami, FL
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545 FXUS62 KMFL 241813 AFDMFL Area Forecast Discussion National Weather Service Miami FL 213 PM EDT Tue Sep 24 2024 ...New SHORT TERM, LONG TERM, MARINE, BEACHES... .SHORT TERM... (Rest of today through Wednesday) Issued at 208 PM EDT Tue Sep 24 2024 Mesoanalysis this afternoon indicates that South Florida is fully underway in the transition between the drier continental airmass that has been in place across the region over the last several days and the plume of deep tropical moisture now just to south. Taking a look at the GOES-East water vapor imagery this afternoon depicts the proverbial "knocking on the door" of the moisture envelope of Tropical Storm Helene advecting slowly northward from the Florida Keys and points southward. -3C to -4C 500mb temperatures aloft indicate that mid- level ridging remains with us, hence the continued presence of mid- lvl dry air and synoptic subsidence over South Florida. This will result in one final afternoon of continued suppression of widespread spatial convection. However even with lackluster synoptic support, mesoscale boundaries such as the Gulf sea-breeze will still produce enough ascent for a few showers and isolated thunderstorms. Seasonably warm temperatures can be expected with highs in the low 90s near the east coast and mid 90s over Interior and SW Florida. As the sprawling circulation and moisture envelope of Helene pushes northward across the northwestern Caribbean Sea overnight, we will start to feel the outer influences of the system. Deep tropical moisture currently to the south of us is forecast to advect northward, as evidenced by PWATs increasing over 2.2 inches by Wednesday afternoon. Rain chances will increase from north to south tonight (although likely confined to the waters and coastal regions). HREF`s LPMM does hint at the potential of coastal convergence taking place overnight along the east coast of South Florida with localized pockets of heavy rainfall that could spark a few localized flooding concerns. A few outer bands from Helene will likely advect northwards across the region on Wednesday with breaks of sunshine in between. Now firmly in the outer fringes of the circulation, our forecast depicts southeasterly winds will become increasingly breezy with gusts 25 to 30mph Wednesday afternoon. Marine and beach conditions will gradually deteoriate throughout the day. && .LONG TERM... (Wednesday night through next Monday) Issued at 208 PM EDT Tue Sep 24 2024 The outer influences of Tropical Storm Helene will continue to arrive across our region late on Wednesday as the center of the system gradually lifts northwards across the Gulf of Mexico. A large moisture envelope associated with the system and climatologically significant precipitable water values will also advect into the region during this time frame. The latest forecast models depict potential precipitable water values of 2.3-2.5 inches which correlates to near max values for the 25th and 26th of September. Forecast models also indicate a long skinny CAPE sounding indicative of ample warm cloud processes that supports heavy rainfall potential. There has also been a consistent signal on the European`s Extreme Forecast Index (EFI) and HREF`s LPMM for coastal convergence along both coasts of South Florida. Given the parameters specified above, the potential certainly remains for heavy rainfall and localized flooding across portions of the area. A Flood Watch has been issued for Collier, Glades, and Hendry counties from Wednesday morning through Friday morning. In general, rainfall amounts from late Wednesday through Friday evening look to range from 2 to 4 inches across inland portions of the region with the potential of higher rainfall totals in the 3-6 inch ballpark across both metro areas. A litany of products continue for our Gulf coast locales outside of the Flood Watch, a Tropical Storm and Storm Surge Watch remains in effect from Bonita Beach to Flamingo. There is the potential of 2-4 feet of storm surge across these areas with potentially locally 6+ in the most vulnerable coastal locations given the large size of Helene and shallow Florida shelf. Rough marine and boating conditions will be felt across the entire region, with the greatest impacts realized across our gulf waters. The probabilities of sustained tropical storm force winds remain confined to coastal Collier throughout the duration of Helene`s passage west of the region, however forecast model guidance indicate a large and fairly robust 850-925mb wind field just above the surface. As the outer feeder bands of Helene rotate across the region, there is the potential for strong wind gusts of tropical storm force across the entire region. A Wind Advisory may have to be considered for the rest of the region not currently covered by tropical products. Outside of the storm surge, flooding rain, and wind threat across the region, the overall parameters for tropical tornadoes appears to be limited by South Florida`s residence time in the northeast quadrant. With the peak time of tropical tornadoes between 18Z-00z due to the mixing of dry air and diurnal heating, the passage of Helene closest to the region on Wednesday night may limit any tornado potential to the coastal areas of Collier depending on track. A second window for potential tornado genesis may materialize across the Lake Okeechobee region during the afternoon hours of Thursday as Helene moves further northward across the eastern Gulf of Mexico. Given the cloud cover and sprawling rain bands, temperatures should remain near climatological norms. While it will not be a washout across the region during this period, convective rain bands will bring periods of gusty winds, blinding rainfall, and the potential of localized flooding across our urban areas. By late Thursday, the center of Helene will be well to the north of the region with the attendant tail/trough situated across the region. This "tail" of higher precipitable waters of 2.3-2.5" will remain draped across our region as breezy southwesterly flow continues across the region. Trailing bands of Helene will work across the region on Friday with the potential of additional localized flooding concerns. In addition, the continued breezy southwesterly flow may result in an additional day of higher than normal water level across the Gulf coast of South Florida. The persistent tail/trough of Helene is forecast to remain situated across the region this weekend which will maintain humidity across the region as the boundary gradually begins to lift northwards. High temperatures throughout the long term period will remain near or slightly above climatological norms across South Florida with highs in the upper 80s to low 90s. && .AVIATION... (18Z TAFS) Issued at 132 PM EDT Tue Sep 24 2024 Mainly VFR conditions will prevail through the rest of the afternoon and into the evening hours. Winds will remain out of the ESE at 10 to 15 kts this afternoon. Scattered showers and storms will form mostly over the interior sections this afternoon away from the east coast terminals. Rain chances will begin to ramp up overnight and into the day on Wednesday. Winds will increase out of the SE early Wednesday morning and could gust to 25 kts as the morning progresses. && .MARINE... Issued at 208 PM EDT Tue Sep 24 2024 Easterly winds will become fresh over the waters today as a gradient strengthens to the north of Tropical Storm Helene in the NW Caribbean. Winds and seas will then turn hazardous on Wednesday as the system intensifies and lifts northward into the SE GOM, with tropical storm conditions possible over the Gulf waters and Gale conditions possible on the Atlantic waters on Thursday. The chances of showers and thunderstorms will also increase Wednesday into the late-week period. && .BEACHES... Issued at 208 PM EDT Tue Sep 24 2024 Minor coastal flooding will remain possible over the east coast today but should generally be spotty as astronomical tides decrease. Moderate to major coastal flooding can be expected over the Gulf coast late Wednesday into Thursday as Tropical Storm Helene strengthens and tracks through the SE Gulf of Mexico. Strengthening onshore flow will result in an extended period of high rip current risk over the east coast (likely through the work week), with potentially hazardous surf developing over the Palm Beaches in the mid-week period. Additionally hazardous beach conditions look likely over the Gulf coast beaches starting Thursday as surf increases in association with Tropical Storm Helene. && .PRELIMINARY POINT TEMPS/POPS... Miami 81 89 79 89 / 60 80 90 80 West Kendall 78 89 79 90 / 60 80 90 80 Opa-Locka 80 90 79 90 / 50 80 90 80 Homestead 79 89 79 89 / 60 90 90 80 Fort Lauderdale 80 88 79 88 / 50 80 90 80 N Ft Lauderdale 80 89 79 90 / 50 80 80 80 Pembroke Pines 81 91 79 91 / 50 80 80 80 West Palm Beach 79 89 79 90 / 40 80 80 80 Boca Raton 80 89 79 90 / 50 70 80 80 Naples 79 90 78 87 / 40 90 90 90 && .MFL WATCHES/WARNINGS/ADVISORIES... FL...Flood Watch from Wednesday morning through Friday morning for FLZ063-066-069-070. Storm Surge Watch for FLZ069-075. Tropical Storm Watch for FLZ069-075. High Rip Current Risk through Thursday evening for FLZ168-172- 173. AM...None. GM...Tropical Storm Watch for GMZ656-657-676. && $$ SHORT TERM...Hadi LONG TERM....Hadi AVIATION...CWC