Area Forecast Discussion
Issued by NWS Melbourne, FL
Issued by NWS Melbourne, FL
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518 FXUS62 KMLB 261117 AFDMLB Area Forecast Discussion National Weather Service Melbourne FL 717 AM EDT Thu Sep 26 2024 .AVIATION... (12Z TAFs) Issued at 720 AM EDT Thu Sep 26 2024 Increasing SE to S winds as Hurricane Helene strengthens over the eastern Gulf and accelerates N/NE next 12-18 hours. Prevailing VFR to start with VCSH at all terminals. An increase in coverage of rainbands will lift northward from southern and western FL peninsula. "Helene" will bring significant aviation impacts to all terminals today as S/SE winds increase 20-30 knots with gusts 45-55 knots possible esp in fast- moving rainbands. AMDs likely needed but have inserted a TEMPO from 18Z-22Z for best chance for IFR/MVFR reductions. Have maintained mention of non-convective LLWS for MCO btwn 00Z-06Z when wind fields maximize just above the sfc. && .PREVIOUS DISCUSSION... Issued at 301 AM EDT Thu Sep 26 2024 KEY MESSAGES: - Hurricane Helene is expected to move toward the Florida Panhandle today. For East Central Florida, numerous downpours, strong wind gusts, and possible tornadoes are the primary threats. Rough, battering surf will produce dangerous conditions at the beaches. - A Tropical Storm Warning is in effect. Preparations for Helene should be completed. Conditions will quickly deteriorate this morning. - Hot and humid Friday into the weekend behind Helene as a plume of deep moisture returns. Heavy rain is also possible over the weekend. ----------Synoptic Overview---------- Hurricane Helene is beginning to accelerate northward over the eastern Gulf of Mexico this morning, located around 400 miles southwest of Tampa as of 2 AM ET. Meanwhile, a cut-off upper low over the Ohio-Mississippi River confluence is slowly meandering southward. On the eastern flank of this cut-off low, Helene is forecast to quickly be drawn poleward. Landfall is expected over the eastern Florida Panhandle this evening as a major hurricane. Thereafter, Helene will penetrate well inland, eventually phasing with the cut-off low over the Tennessee Valley by Friday after a rare occurrence of the Fujiwhara Effect over the Southeastern United States. There is high confidence in this solution among the available model guidance. This weekend and into early next week, the guidance suggests the upper low will slowly weaken north of a building H5 ridge axis over Florida. This ridge is then forecast to slowly retreat into the Atlantic by the middle of next week but with increasing spread in the upper-air pattern noted over the Eastern U.S. Boundary-layer flow should remain southwesterly behind Helene through the weekend before becoming light early next week. A tail of deep tropical moisture will be funneled from the Caribbean across Florida through the weekend before total moisture values dip closer to seasonal norms as we push deeper into next week. -----Short Term Mesoscale Features----- As Helene moves into the NE Gulf today, the Florida Peninsula will reside on its eastern flank. The wind field will expand, characterized by 3K to 5K FT AGL winds reaching 50-75 KT over our district by this afternoon. Such a remarkable mass response will advect rich tropical moisture (PWs >2.5"), intervals of convergence, and at least moderate destabilization (MLCAPE ~ 1000 J/kg). In addition, winds will back SSE at the surface, generating 200-400 m^2/s^2 of ESRH. This environment will be capable of producing periodic bands of rain and storms along with the threat of tornadoes and enhanced wind gusts. 26/00Z HREF proximity soundings also indicate some potential breaks in the thick overcast which would promote deeper mechanical mixing of the strong boundary layer winds to the surface. Momentum transfer algorithms agree with this assessment. -------Sensible Weather & Impacts------- Through Today/Tonight... Wind: After sunrise, wind speeds will start to ramp up and gusts will begin to take place more frequently. By midday, a few gusts exceeding 40 mph will begin to occur, particularly on the coast and near/south of Orlando. These gusts will become frequent and ramp up well into tropical storm force this afternoon and into the evening. The timeframe for the highest potential gusts looks to reside between 2 PM and 9 PM. In that window, there is a 60% or greater probability of wind gusts exceeding 50 MPH roughly from Melbourne to Okeechobee and points northwest, as well as along the immediate Treasure Coast. West of Orlando, including Lake County, there is a 40-60% chance for wind gusts to near or just over 60 MPH. The frequency of these gusts will be greater if more breaks in the overcast occur and within bands of rain/storms. Wind gusts of this magnitude can turn lightweight objects into flying debris, cause sporadic power interruptions, and perhaps result in some tree or minor structural damage. Please remain indoors if at all possible. Tropical storm force gusts will diminish after midnight. Tornadoes: The Storm Prediction Center has highlighted almost all of the district in a Slight Risk (level 2 of 5) for severe storms, the primary threat being a few tornadoes. A Marginal Risk exists for St Lucie & Martin Counties. We will be monitoring fast-moving rain/storm bands for this potential. Have multiple ways of receiving warnings today! Flooding Rain: A Flood Watch remains in effect for East Central Florida. On the whole, additional rainfall totals will average 1-3". However, locations that see repeated rainbands (on an isolated basis) would be able to exceed those values which could lead to some minor flooding issues. Max-member HREF rainfall shows a non-zero threat of a few locations reaching 4"+ of rain. If you encounter a flooded roadway, turn around, don`t drown. Beaches/Marine: Here`s the takeaway... stay away from the water today! A High Surf Advisory is in effect for battering surf which may run up to the dune line. This could cause minor beach erosion. Additionally, numerous life-threatening rip currents and a powerful longshore current will exist. Seas will rapidly build and become dangerous. With breaks in the rain and perhaps even a few hints of sun, high temps should still reach the upper 80s to low 90s. Combined with the high humidity, heat indices may reach 105F this afternoon in a few spots. Friday-Weekend... A tail of deep tropical moisture will oscillate from South-Central FL on Friday to Central Florida on Saturday and Sunday. Beneath it, scattered-numerous (50-70%) shower and storm coverage is forecast particularly in the afternoon/evening hours. While brief gusty winds can`t be ruled out, our main concern is additional rounds of heavy rain over already saturated ground. We will monitor for the risk of flooding in a few locations once we better pin down the coverage and extent of the expected rain/storms. Without question, high humidity persists with dew points well into the mid/upper 70s. Combined with the offshore flow, low to even a few mid 90s are forecast. Heat index readings from 102-107F are currently expected each afternoon. This could get us very close to Heat Advisory territory. Next Week... As the upper ridge sits nearby, the deep tropical moisture overhead will trend closer to normal. Some members show bouts of even drier air infiltrating the area from time to time, but confidence lessens overall. This yields continued 30-50% shower/storm coverage each day with highs in the upper 80s to lower 90s. Heat indices will subtly "dip" closer to 98-103F as surface moisture trends toward normal values. && .MARINE... Issued at 301 AM EDT Thu Sep 26 2024 BOTTOM LINE: Dangerous Marine Conditions From Helene through early Friday... Today/Tonight... Hurricane Helene will produce extremely dangerous marine conditions. All operators should remain in port through tonight. Nearshore seas are forecast to peak from 9-11 FT by this evening, increasing to 10-15 FT in the Gulf Stream. Sustained tropical-storm-force winds are likely along with southerly gusts as high as 50-55 KT. Winds will start to decrease overnight but tropical storm force gusts will persist through the overnight. Numerous showers and storms with waterspouts are possible! Friday-Sunday... Seas quickly subside through the period: 5-7 FT nearshore / 6-10 FT on Friday, 2-3 FT nearshore / 3-5 FT offshore this weekend. However, fresh southerly winds continue at 20-25 KT Friday before becoming SW 8-15 KT this weekend. Scattered-numerous showers and storms with offshore-moving activity expected. && .PRELIMINARY POINT TEMPS/POPS... DAB 90 78 92 76 / 80 60 40 30 MCO 90 79 91 77 / 80 50 50 30 MLB 90 79 92 77 / 70 50 70 50 VRB 90 78 92 77 / 70 50 70 50 LEE 88 78 90 77 / 90 70 30 20 SFB 88 79 91 77 / 80 50 50 30 ORL 89 80 91 78 / 80 60 50 30 FPR 90 79 91 77 / 70 50 70 50 && .MLB WATCHES/WARNINGS/ADVISORIES... FL...Tropical Storm Warning for FLZ041-044>046-053-058-141-144-154- 159-164-247-254-259-264-347-447-547-647-747. Flood Watch through Friday morning for FLZ041-044>046-053-058- 141-144-154-159-164-247-254-259-264-347-447-547-647-747. High Surf Advisory until 11 AM EDT Friday for FLZ141-154-159-164- 347-447-647-747. AM...Tropical Storm Warning for AMZ550-552-555-570-572-575. && $$ DISCUSSION...Heil AVIATION...Kelly