Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 290002 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 800 PM EDT Sat May 28 2016 .SYNOPSIS...
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Tropical storm Bonnie off the Southeast coast will track northwest to the South Carolina coast tonight, stall along the South Carolina coast on Sunday, then track slowly northeast along or just offshore the North Carolina coast through mid-week.
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&& .NEAR TERM /Through Tonight/...
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As of 100 PM Saturday... As TS Bonnie tracks NW toward the Southeast coast this afternoon, an increasingly moist/tropical air mass will advect inland from the Atlantic, aiding in marginal diurnal destabilization (~100-250 J/kg mlcape) this afternoon across portions of the southeast coastal plain. Though shallow diurnal convection is unlikely to develop directly over portions of the coastal plain today given little forcing and very weak instability, the airmass in place by late afternoon should be sufficient to maintain upstream showers (on the seabreeze or moving onshore the Carolina coast) as activity advects inland via 15-20 kt E/ESE steering flow. Will indicate an increasing chance for showers late this afternoon and evening from the SE coastal plain west to the sandhills and north to the Hwy 64 corridor. Expect highs in the mid 80s, warmest over the northern Piedmont /Triangle/ and northeast coastal plain. -Vincent
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&& .SHORT TERM /Sunday through Sunday night/... As of 200 PM Saturday... TD#2 is expected to become a low-end tropical storm prior to landfall (or closest approach to the SC coast) around 12Z Sunday morning. The precise evolution of this system (the track in particular) will heavily influence the location/amount of rain that falls across central NC Sunday into Sunday night, as demonstrated by the wide variety of solutions obtained from various convection allowing models. As a result, the location(s) or area(s) that will receive the heaviest rainfall remain difficult to pin-down at this time. Based on the official NHC guidance, one would expect the axis of heaviest rain to become oriented N-S or NNE-SSW in vicinity of Highway 1 or I-95. Locally heavy rainfall amounts of 1-3" will be possible in this area. High temps will depend primarily upon cloud cover and precipitation, which should be pervasive over much of central NC. As such, will indicate highs in the mid/upper 70s, though lower 80s will be possible if/where there are breaks in cloud cover. Expect lows in the mid/upper 60s (possibly near 70F) Sunday night with a tropical airmass in place, southeasterly flow off the Atlantic, lingering cloud cover, and showers. Hazardous Weather: A localized potential for flash flooding will be present Sun/Sun night, primarily in urban areas. Given the anticipated location of TD#2 (expected to stall in southern SC during the day Sun), the best low/mid-level shear (mini-supercell/ tropical tornado potential) is expected to remain south of central NC, along and near the coast from Charleston SC north to Wilmington, NC. -Vincent && .LONG TERM /Monday Through Saturday/... As of 310 pM Saturday... Monday through Wednesday: The low associated with tropical depression two will be captured in a weakness or trough in the upper- level pattern over the southeast U.S. and a 590m ridge over the western Atlantic. This will result in a very slow east to northeast drift of the surface low as the ridge over the Atlantic weakens. The best precipitation chances during the period should be focused across central the eastern half of NC and in our forecast area across the coastal Plain/Sandhills and the eastern Piedmont. This is given the northward advection of deep layer moisture on the backside of the offshore ridge and to the east of the trough axis combined with some modest forcing for ascent east of the trough and low-level convergence resulting from the tropical circulation and frictional convergence in the coastal region. The greatest rain chances during the period will likely be on Monday east of U.S. route 1 where rain coverage and amounts will be greatest. Rain chances decrease somewhat on Tuesday and Wednesday. Rainfall amounts will be rather localized with slow moving bands and clusters of showers/storms driving precipitation amounts. Average amounts through the period will range around an inch to an inch and half from I-95 east, a half inch to an inch between U.S. 1 and I-95 and a half inch or so west of U.S. 1. While these amounts aren`tterribly impressive, we fully expect localized higher amounts during the period. Highs during the period will generally range in the lower 80s on Monday and the lower to mid 80s on Tuesday and Wednesday with morning lows in the mid to upper 60s. Thursday through Saturday: A slow moving trough pushes east across the plains on Thursday and extends from the eastern Great Lakes to the northern Gulf of Mexico on Friday and Saturday. The eastern progression of the trough slows as heights rise off the Southeast coast and the remnants of TD two eventually dissipate off the Northeast coast. The developing southwesterly flow ahead of the approaching upper trough leads to another period of moisture transport with increasing instability. After a modest decrease precipitation chances on Thursday in between systems and with a minimum which should result in a period of unsettled weather for Friday into Saturday with showers and thunderstorms. highs will mainly range in the lower to mid 80s with lows in the 60s. -blaes && .AVIATION /00Z Sunday through Thursday/...
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As of 8 PM Saturday... 24-Hr TAF Period: A plume of tropical moisture will advect into the area overnight and into the day on Sunday as TS Bonnie moves onshore between Charleston and Beaufort, SC. Ceilings are expected to lower to MVFR/IFR from SE to NW between 06z-12z, with increasing chances for showers and associated sub-VFR visibilities expected at all terminals by mid/late morning. Sub-VFR ceilings and visibilities will persist through the afternoon and evening with numerous heavy rain producing showers across the area, along with a threat for isolated thunderstorms mainly across the eastern terminals. Looking Ahead: Unsettled weather with continue Sunday night through Monday as TS Bonnie and associated tropical moisture plume linger across the area. Significant uncertainty persists whether or not remnants of Bonnie stalls along the Carolina coast through mid to late week. At this time, a chance for diurnally driven convection and morning stratus are expected to be the primary aviation hazards.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Vincent NEAR TERM...Vincent SHORT TERM...Vincent LONG TERM...blaes AVIATION...CBL/Vincent

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