640 FXUS62 KMFL 131802 AFDMFL Area Forecast Discussion National Weather Service Miami FL 202 PM EDT Mon Sep 13 2021 .AVIATION(18Z TAFS)... Moist easterly flow will continue to support intermittent showers and storms moving onshore over the east coast metro areas through the period. The sporadic nature of the convection precludes mention of restrictions at this time. A brief lull in storms is possible later this afternoon for the east coast, as storms spread westward toward the Gulf Coast where MVFR/IFR conditions are expected at APF. An additional uptick in nocturnal convection is possible for the east coast overnight. && .PREV DISCUSSION... (Issued 1138 AM EDT Mon Sep 13 2021) UPDATE... No major updates to the forecast this morning as different waves of convection are pushing across the Atlantic into South Florida. High resolution guidance continues to support the focus for convection shifting westward for the afternoon, in keeping with the previous shift's forecast philosophy. Some strong thunderstorms, including for potentially a severe storm or two, are certainly possible this afternoon and early evening over Southwest Florida. The focus for this potential comes with boundary collisions that some high-res guidance members have been suggesting may occur a little later in the afternoon. Made some minor tweaks to the hourly temperatures grids to account for the rain-cooled air over portions of the east coast metro this morning. No additional updates are anticipated through midday. Have a great Monday! PREV DISCUSSION... (Issued 243 AM EDT Mon Sep 13 2021) MODERATE RISK OF RIP CURRENTS EAST COAST BEACHES TODAY... STRONG TO EVEN ISOLATED SEVERE STORMS TODAY AND AGAIN ON TUESDAY... WET CONDITIONS EXPECTED THROUGH THE WEEK AND INTO NEXT WEEKEND WITH POSSIBLE HEAVY RAINFALL... SHORT TERM... (Today)... High pressure will remain over the western Atlantic waters as a weak trough wave over the Northern Bahamas moves west northwest across South Florida. This will keep an light easterly wind flow in place along with the deeper tropical moisture. The best chance of showers and thunderstorms will be over the east coast metro areas this morning before shifting into the interior and west coast metro areas this afternoon into this evening. The PWAT values will be in the 2 to 2.1 inch range over South Florida today which is near the ninety percentile range for this time of year. Therefore, there could be some heavy rainfall today over South Florida with the showers and thunderstorms. The 500 mb temperatures will also be cooling through the day hours from -6C to -7C, as a mid level trough moves southward from North Florida into South Florida. This will allow for a few storms to become strong this afternoon into this evening over the interior and west coast metro areas especially where the sea breezes collide. Highs today will be in the lower 90s over most areas, except upper 80s to near the east coast metro areas. This will allow for the heat indices to get up into the lower 100s except upper 90s east coast metro areas. (Tonight)... The surface high pressure over the Western Atlantic waters will start to weaken, as the weak tropical wave becomes more of a weak low level through over South Florida. This will keep the deep tropical moisture in place over the region and allow for the easterly wind flow to weaken to light flow over South florida. This should allow for a inverted east coast trough to set up along the east coast metro areas late tonight allowing for the possibility of showers and thunderstorms to develop over the east coastal areas or just of the east coast late tonight. If this weather pattern setup for late tonight, then there could be the potential for heavy rainfall over portions of the east coastal areas of South Florida late tonight. Will continue to monitor the latest short range models through today for the potential of heavy rainfall event for late tonight. Lows tonight will also remain warm with mid to upper 70s over most areas with around 80 over the east coast metro areas. Heat indices will be in the upper 80s to near 90 over the east coast metro areas tonight. (Tuesday)... The surface high over the Western Atlantic waters will continue to weaken as the low level trough remains nearly stationary over South Florida. This will keep the deep tropical moisture in place with the 2 to 2.1 inch PWAT values over South Florida. Therefore, scattered to numerous showers and thunderstorms will again be possible over South Florida on Tuesday along with heavy rainfall. At the same time, the mid trough will remain nearly stationary over South Florida keeping the 500 mb temperatures in the -7 to -8C range. There will also be a mid level jet of 50 knots coming across South Florida from the north around the mid to upper level high over the Gulf of Mexico. This will allow for some strong to even an isolated severe storm to develop over South Florida especially in the afternoon and evening hours. The primary impacts from the strong or severe storms will be gusty winds and frequent lightening strikes. Highs on Tuesday will be cooler than today due to more coverage of the showers and thunderstorms with highs only getting up to around 90 over the interior areas and mid to upper 80s over the metro areas. LONG TERM... (Tuesday Night through the Weekend): One word to describe the long term period: wet. Meridional flow continues through the end of the work week with multiple rounds of vort maxima passing through the area. With the ridge axis displaced well to the north of the CWA, rich moisture laden onshore flow will prevail throughout the period, keeping PW's in excess of 2 inches. With moisture forecast to exceed the climatological mean, high end PoPs are in the forecast, with max PoPs in the 60 to 70 percent range for the time being. Note that these values are capped due to uncertainty so they very well may increase as confidence builds. Easterly flow will favor the western half of the peninsula for highest coverage during the afternoon hours. Thus, expect showers and thunderstorms to develop near the east coast metro areas late in the morning and early in the afternoon, then becoming more numerous and robust over interior and west coast areas late in the afternoon as sea breezes push inland. Main hazards with any storm that forms will be heavy rainfall, frequent lightning, gusty winds, and flooding. Towards the middle-end of the work week and into the weekend, the familiar face of uncertainty grows and confidence wanes as global models struggle with a potential wave approaching the area from the tropics. They continue to differ in intensity; however, they do remain consistent on maintaining the wave east of the Bahamian Islands before pushing it NE towards the Mid-Atlantic Seaboard while simultaneously coming a little closer together in regards to timing. With an expected breakdown in high pressure during the end of the work week, low-level winds should veer from the SE. With latest guidance, steering flow is now from the SE/SSE. This will enhance the tropical moisture advection from the south and provide enough moisture for deep convection to develop each day. PoPs will be kept capped at around 60 percent and wait for better consistency in upcoming model runs before going higher (or lower). However, there should be enough thermodynamic support and moisture for a few cells to become strong, especially at the peak of daytime heating. High temperatures in the upper 80s to lower 90s with overnight lows in the mid to upper 70s. Depending on cloud coverage and expected convection, high temps may be overdone a degree or two. Heat indices in the mid-upper 90s. MARINE... The winds will be easterly at around 10 knots today before decreasing to 5 to 10 knots tonight into Tuesday. The winds will then continue to decrease to 5 knots or less for the middle to end of the week while slowly swinging to more of a southeast direction. The small northeast swell that been occurring over the Palm Beach Atlantic waters will slowly dissipate today into tonight. Therefore, the seas will remain at 2 to 3 feet today before decreasing to 2 feet or less for rest of the week in the Atlantic waters. The Gulf waters will remain at 2 feet or less for the whole week. BEACH FORECAST... The threat of rip currents will remain in the moderate range today along the east coast beaches due to the easterly wind flow. The threat of rip currents will then decrease along the east coast beaches trough rest of the week, as the wind flow decreases. The threat of rip currents along the west coast beaches will remain low. && .PRELIMINARY POINT TEMPS/POPS... Miami 79 88 78 90 / 60 70 40 60 West Kendall 77 88 76 91 / 50 70 40 60 Opa-Locka 79 88 77 90 / 60 70 40 60 Homestead 79 87 75 89 / 60 70 50 60 Fort Lauderdale 80 87 78 89 / 60 70 40 60 N Ft Lauderdale 79 87 78 89 / 60 70 30 60 Pembroke Pines 79 88 77 90 / 60 70 40 60 West Palm Beach 77 88 77 90 / 50 70 30 60 Boca Raton 79 87 78 89 / 60 70 30 60 Naples 76 89 75 89 / 50 80 40 60 && .MFL WATCHES/WARNINGS/ADVISORIES... FL...None. AM...None. GM...None. && $$ Aviation...Weinman Today through Tuesday and Marine...BNB Tuesday Night through Sunday...Fell Visit us at weather.gov/miami Follow us on Facebook and Twitter at: www.facebook.com/nwsmiami www.twitter.com/nwsmiami