Area Forecast Discussion
Issued by NWS Wakefield, VA
Issued by NWS Wakefield, VA
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951 FXUS61 KAKQ 261820 AFDAKQ AREA FORECAST DISCUSSION National Weather Service Wakefield VA 220 PM EDT Thu Sep 26 2024 .SYNOPSIS... Hurricane Helene intensifies today, before making landfall on the Florida Gulf Coast this evening. The remnants of Helene will then pass well west of the area on Friday. Drier conditions briefly return on Saturday, followed by unsettled weather Sunday through next Tuesday. && .NEAR TERM /THROUGH TONIGHT/... As of 1110 AM EDT Thursday... Key Message: - Isolated to scattered showers redevelop this aftn, mainly W of I-95, with only a slight chance to the east. The latest wx analysis indicates Hurricane Helene moving N over the eastern Gulf of Mexico (105 MPH Cat 2 as of the 11 AM NHC advisory), with ~1028mb sfc high pressure anchored across Atlantic Canada, bringing E-SE onshore low level flow. A potent upper low is spinning across the lower OH/mid MS Valley, bringing southerly flow aloft from the eastern Gulf of Mexico north to the eastern CONUS. Mainly dry conditions are noted across our entire forecast area and latest visible satellite even shows some sun peaking through over SE VA and on the Eastern Shore. Warm and rather muggy with temps already near 80 E of I-95, with mid 70s to the W. Expect mostly dry conditions through this morning, with some showers/isolated storms expected to redevelop in the aftn along and W of I-95. Will have PoPs ~40% in the Piedmont (50% across the far SW), tapered to only 15-20% to the east. Hurricane Helene will be moving NNE towards northern FL during the aftn, with a forecast landfall in the Big Bend region tonight per the latest NHC track. Partly to mostly cloudy into this afternoon and have increased highs a degree or two into the 80-82 F range given the current trend in obs. Into tonight, we should remain too far removed from Helene for anything more than a low chc for showers and perhaps a few embedded tstms (mainly W of I-95). Far SW portions of the local area may see an increase in PoPs towards sunrise Fri, but overall the main batch of precip will not arrive until the day Friday. Warm and humid with lows in the upper 60s to lower 70s. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 405 AM EDT Thursday... Key Messages: - Helene weakens and tracks well west of the area Friday, bringing the potential for moderate to locally heavy rain and a tornado threat (mainly to southern VA and NE NC zones). - Mainly rain-free and warm/humid Saturday. Rain chances rapidly increase after daybreak Friday, with PoPs rising to likely to categorical over the W/SW 1/2 of the area, overspreading the entire CWA by late morning or early aftn. The overall trends with respect to total QPF are similar or slightly lower compared to the previous model cycle. The ensemble means are less than 0.50" over the NE portion of of the CWA to ~1.00" over the western piedmont, but as usual much higher local amounts will be possible. Perhaps the greater concern will be for a tornado threat sometime from later Fri morning through Fri aftn as instability develops across NC and into at least southern portions of VA. Ample low level shear will be in place with strong SSW flow aloft and SE low level winds, yielding large, curving hodographs. Farther north, the amount of instability will be less so the threat is lower. Uncertainty in the exact track of Helene makes the severe threat somewhat uncertain, but there is enough consensus for SPC to have NE NC into a Day Slight Risk (primarily for the 5% TOR threat), with a marginal (2% TOR threat) into southern and central VA (roughly to the I-64 corridor). A dry slot moves in from the south late Fri aftn/Friday evening into Friday night, bringing an end to the precip. On Saturday, the remnants of (weakening) Helene will be located well off to our west over western KY. Drier weather returns outside of some low- end rain chances across the NW late. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 415 AM EDT Thursday... Key Message: - Multiple low-end chances of rain Sunday through Tuesday early from the post tropical remnant of Hurricane Helene - Drier and cooler air arrives mid to late next week Latest ensemble guidance indicates that the remnant low of Hurricane Helene will stall and slowly weaken across the lower OH or upper TN Valley Sunday, with the upper low gradually shifting to the east through Tuesday. Overall, this will keep conditions unsettled, with daily chances for showers and a few thunderstorms. Temperatures Sunday will remain warm with highs into the upper 70s to lower 80s, then trending cooler Mon-Tue as the upper low will be more centered near the region, bringing highs in the 70s. Lows will generally be in the 60s. Model differences remain as to how fast the upper low and the associated cold front pass by the region towards the end of the period with the GFS/GEFS being the most progressive while the ECMWF/ENS and Canadian/GEPS are weaker with the initial upper low and a bit slower. Will continue to forecast a drying trend, and significantly lower humidity arriving by Wed with highs in the 70s and lows Wed night and beyond into the 50s for most. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... As of 230 PM EDT Thursday... Scattered showers remain to the NW of RIC. High clouds from Hurricane Helene with VFR conditions are present across the area. Some lower clouds (around 2,000ft) are present across most of the area, but they are mainly scattered. Winds are primarily SE at 5- 10kt. MVFR CIGs will begin overnight with the piedmont reaching lower heights first. Patchy fog near SBY and PHF is possible before sunrise. Cloud heights will decrease throughout the day to IFR and locally LIFR as rain chcs increase. There is a chc for scattered storms/tstms starting tomorrow afternoon but timing and coverage are uncertain. Locally reduced visibility and higher winds are expected in any shower or storm. After sunrise, winds will pick up and gusts around 20kt are possible across the area. Outlook: The direct impacts of Hurricane Helene and its remnant low are somewhat uncertain, but Friday afternoon and into overnight has a continuing chc of storms. While Friday is likely wet, Saturday will be drier. A chc of showers is possible with unsettled wx Sun- Mon. && .MARINE... As of 405 AM EDT Thursday... Key Messages: - Small Craft Advisories have been extended into late Friday for all Atlantic zones due to persistent seas above 5 ft. - Southeast winds increase on Friday bringing the potential for Small Craft conditions in the Chesapeake Bay, lower James River, and Currituck Sound. High pressure has moved off the eastern Canadian coast with Hurricane Helene making northward progress into the eastern Gulf of Mexico. Winds are generally E or SE at 5-10 kt across the local waters. Waves are mainly 1-2 ft in the Chesapeake with 2-3 ft near the mouth. Seas range from 3-5 ft, highest away from the immediate coast. Southeast flow has overspread the waters as high pressure well to the north continues to translate eastward/offshore. This has allowed near-shore wave heights to finally fall below 5 ft but have maintained SCA headlines for all coastal waters as heights remain 4- 5 ft farther offshore. Hurricane Helene continues to intensify over the extremely warm waters of the eastern Gulf. The storm is forecast to make landfall along the Florida Big Bend early this evening. Helene continues quickly north tonight into Georgia. SE winds 5-10 kt continue today and tonight before the gradient strengthens locally on Friday. Winds increase to 15-20 kt with gusts to 25 kt on Friday into Friday evening and SCA headlines are likely for the Chesapeake Bay, lower James, and Currituck Sound. The gradient relaxes early Saturday as the remnant circulation from Helene gets shunted NW on the northern periphery of an upper level low. Waves in the bay increase to 2-3 ft with 3-4 ft likely near the mouth Friday afternoon and evening. Calmer conditions are expected on Saturday and even the seemingly never-ending SCA headlines for the coastal waters may even be allowed to expire. For now, have only extended the ongoing coastal waters SCAs for an additional six hours into Friday night with less confidence that 5 ft seas will persist toward sunrise Saturday. Uncertainty increases for Sunday into next week with the 00z GFS the most bullish on some of Helene`s energy combining with the lingering upper low to result in the development of another area of (non-tropical) low pressure along the NC coast. Will show ENE winds increasing to around 15 kt for now pending better agreement in the models. High rip current risk continues for all beaches today and Friday given 3-5 ft nearshore waves and swell periods 10-12 seconds. && .TIDES/COASTAL FLOODING... As of 405 AM EDT Thursday... Key Messages: -Tidal departures continue to fall across the region. - Coastal flood advisories have been issued for the next two high tide cycles for the tidal Potomac and Rappahannock as well as bay side portions of the MD Eastern Shore. Tidal departures continue to fall this morning, but remain highest (1.5-1.75 ft) in the upper Chesapeake Bay, along the tidal Potomac and Rappahannock, and on the bay side of the MD Eastern Shore. Coastal flood advisories have been issued through late this evening. Water levels fall further to end the week and any nuisance-minor flooding will likely be constrained to tidal Potomac and bay side of the MD Eastern Shore. Latest guidance does show the potential for increasing anomalies late Friday across the middle and upper bay with the potential for minor to locally moderate coastal flooding at Bishop`s Head and Lewisetta. Lastly, will continue to watch areas adjacent to the Currituck Sound (including Back Bay) and the Albemarle Sound today into Friday as SE winds could push already elevated water levels up further into minor flooding thresholds. As of 405 AM EDT Thursday: Consecutive high tides reaching at least Minor Flood with this event: - Lewisetta (P.O.R. since 1979): 18 (with several more to come), previous record was 8 in Oct 2021, Oct 2019, Oct 2015. - Cambridge (P.O.R. since 1980): 13 (with this morning`s high tide unlikely to reach minor flood), previous record was 5 in Oct 2021, Oct 2019, Sep 2018, Oct likely 2011. Consecutive high tides reaching at least Moderate Flood with this event: - Lewisetta (P.O.R. since 1979): 7 (with additional moderate flood unlikely), ***tying the record of 7 in Oct 2015*** && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...Coastal Flood Advisory until 1 AM EDT Friday for MDZ021>023. NC...None. VA...Coastal Flood Advisory until 1 AM EDT Friday for VAZ075-077. Coastal Flood Advisory until 11 PM EDT this evening for VAZ076- 078-085-521-522. MARINE...Small Craft Advisory from 7 AM Friday to midnight EDT Friday night for ANZ630>638. Small Craft Advisory until 1 AM EDT Saturday for ANZ650-652- 654-656-658. && $$ SYNOPSIS...LKB NEAR TERM...LKB/SW SHORT TERM...LKB LONG TERM...KMC/LKB AVIATION...KMC/LKB/TMG MARINE...RHR TIDES/COASTAL FLOODING...