Preliminary Forecasts
Issued by NWS
Issued by NWS
362 FXUS02 KWNH 230700 PREEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Mon Sep 23 2024 Valid 12Z Thu Sep 26 2024 - 12Z Mon Sep 30 2024 ...Tropical system development threat for the Gulf of Mexico and Central to Eastern Gulf Coast/Southeast mid-late week... ...Guidance/Predictability Assessment... Models and ensembles seem to be finally trending towards a more consistent flow pattern across the CONUS during the medium range period, which includes the eventual track of a possible tropical system through the Gulf of Mexico and towards the central-eastern Gulf Coast region late this week. Models have trended towards more splitting of flow and a cutoff upper low lingering over the middle Mississippi Valley much of the period. This should help to pull a Gulf tropical system northward and faster than previous guidance. Latest QPF/ERO forecasts from WPC and NHC thoughts reflected this. Still, very little confidence in any of the specifics associated with especially the tropical and until an actual system forms, models will likely continue to flip-flop. Should also note that the ensemble means are a little slower than their deterministic counterparts, which highlights the uncertainties in individual ensemble members. Elsewhere across the CONUS, there is some timing and amplitude uncertainty with another shortwave into the Western U.S. late weekend and reinforced troughing/a closed low near the Northeast. The WPC medium range product suite was mainly derived from a composite blend of the generally compatible GFS/ECMWF and ECMWF ensemble means for Thursday into Saturday whose forecast cluster was closest to NHC thoughts on potential Gulf tropical development and track. After this, favored a solution closest to the emsemble means given increasing uncertainty. This plan is overall faster than WPC continuity with the Gulf Coast system and faster to bring copius rainfall to the east-central Gulf coast and the Southeast. ...Weather/Hazards Highlights... The National Hurricane Center (NHC) and the Weather Prediction Center among others continue to monitor possible tropical system formation in the Caribbean that looks to lift into the Gulf of Mexico to threaten maritime interests and the central to eastern Gulf Coast/Southeast mid-late week. Given the system has yet to form, strength and track remain uncertain, but the picture us getting clearer. The vast bulk of recent guidance offers a growing signal for impactful weather, including a threat for heavy rainfall/winds/surf for the central to eastern Gulf Coast/Florida, with impactful weather possible through the Southeast and vicinity late week into the weekend. There has been an overall faster trend in recent guidance. By Day 4/Thursday, there are expansive WPC Marginal and Slight Risk Excessive Rainfall Outlook (ERO) areas spread northward across the Southeast. If the current forecast hold, it is likely at least a moderate risk will be needed closer to the coast for this time period, but with ongoing uncertainty, it still seems prudent to hold off for now. Regardless, latest models and ensembles continue to support a heavy rainfall/storm surge/flooding threat across the central to eastern Gulf Coast region both with advance moisture feed inland and with landfall. The threat would continue for Day 5/Friday with system proximity and moisture feed back across the Southeast and into the Tennessee Valley/Mid-South to intercept a slow moving closed low. Elsewhere, upper trough energy will dig through the Northeast mid- late week. A wavy surface front will work offshore, leading to coastal low development and exit. Expect a period of enhanced rain over Maine Thursday with a closed upper low and wrapback moisture. Out West, most areas should be dry. The Washington coastal ranges and Cascades will be an exception with enhanced rain and highest elevation snow potential late week with Pacific system passages. Schichtel Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml https://www.wpc.ncep.noaa.gov/#page=ovw $$