Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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271 FXUS62 KRAH 281030 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 625 AM EDT Sat May 28 2016 .SYNOPSIS...A tropical depression off the Southeast coast will drift slowly northwest toward the South Carolina coast through Sunday, before turning northeast and tracking off the southeast North Carolina coast through Wednesday. && .NEAR TERM /through tonight/... As of 250 AM Saturday... What is currently TD2 (projected to become TS Bonnie) is located off the SE coast east of JAX early this morning, and it will continue tracking NW toward the Southeast coast today and tonight, following a path along the weak NW-to-SE-oriented mid level shear axis now extending across SC and SW NC. Bermuda high pressure continues to nose westward across NC, providing subsidence and mostly clear skies through this morning, although this will give way to the slowly incoming cloud shield associated with TD2 later today. While the TD is not expected to move close to shore until late Sun, the strengthening low-fetch low level southeasterly inflow on the TD`s north side will draw plentiful moisture into central NC starting late this afternoon, with PW values aoa 1.5" supplanting the sub- 0.75" PW now in place over the area by this evening. The latest model runs are slower in bringing substantial precip into central NC, depicting little to no coverage outside of the far SE counties until late today. Based on the stubborn nature of the Bermuda surface ridge along with the mid level dry air noted on forecast soundings, the current cloud trends, and the passage of the bulk of the initial DPVA to our south within the mid level shear axis, have delayed precip onset, will focus pops on the SE only for much of the day. Upper divergence ramps up after nightfall along with moist upglide, and PW values are projected to approach 2.0 inches (mainly east half) tonight. Will retain a steady upward trend of pops from SE to NW, reaching likely pops areawide by late tonight with an abundance of deep moisture and improving dynamic forcing for ascent. Expect highs today of 82-87, "coolest" over the SE given the earlier clouds and precip arrival. Warm lows tonight of 63-69. -GIH && .SHORT TERM /Sunday through Sunday night/... As of 325 AM Saturday... This is shaping up to be a very wet day, potentially lasting into the night, with locally heavy downpours likely over a portion of the Carolinas, although the details of who precisely will get the heaviest precip and exactly how much will fall remain somewhat uncertain. The center of TD2/TS Bonnie is expected to approach CHS Sun morning before turning right and then tracking NE just off the central and NE SC coastline through Sun night. Moderate upper divergence in the right entrance region of the southerly Great Lakes / E Ontario jet will persist, and as the weak shear axis edges slightly to the NE and overhead, we`ll see increasing DPVA as well. This lift will be acting on a very moist column featuring PW of 1.5- 2.0" (highest east) and a deep LCL-to-0C layer nearing 4 km, favoring efficient warm rain processes. The weak mid level winds will also mean slow cell movement and possibly prolonged moderate to heavy rainfall. The risk of heavy rain appears to be best over the Coastal Plain, where the juxtapositioning of the greatest moisture and lift is best, but there are enough differences among the models regarding timing and placement to preclude issuing any sort of flood watch at this time. Additionally, the Coastal Plain`s sandier soil can typically hold more water, raising the threshold for flooding in this area. Will monitor this threat closely today. Will carry tonight`s likely pops through Sun, trending down to chance pops Sun night west to east with loss of heating and passage of vorticity lobes just to our east leading to reduced DPVA and lower dynamic forcing in general. Highs Sun 76-82 and lows Sun night 63-68, all under cloudy skies. -GIH && .LONG TERM /Monday Through Friday/... As of 300 AM Saturday... Monday and Tuesday: Tropical Depression Two will continue to spin along the Carolina coast on Monday somewhere in the vicinity of Myrtle Beach and heading northeastward towards the NC/SC border by Monday night. The storm should be in a weakening mode possibly moving from tropical storm strength back down to tropical depression strength sometime during the day on Monday. Regardless of the strength...models point to a large amount of moisture across the eastern half of the state. Will keep pops in the high chance to likely range with slight chance of thunder Monday afternoon. The depression will shift slightly eastward on Tuesday as surface high pressure builds in over the Ohio Valley. This will quickly move northward though and weaken and is unclear how much of an effect it will have on precipitation. Therefore expect lower chances Tuesday but still a good chance for wet weather east of I-95. Highs during this period in the low 80s with lows in the mid 60s. Models diverge on Wednesday as the handling of Tropical Depression Two becomes more uncertain. The ECMWF keeps the storm lingering off of the coast while the GFS breaks it down. Either way a low pressure system over the northern plains with a frontal system extending down the Mississippi Valley will start to work eastward but will be very slow in doing so. This will leave a very moist and warm airmass in place, but a stagnant one without much forcing. Therefore expect diurnal chances for rain and possibly thunder as well Wednesday and Thursday. Highs and lows remain steady in the mid 80s and mid 60s respectively. There is very good agreement in the models regarding the frontal system finally making it to the area on Friday as an upper trough digs out of the Great Lakes. This will increase the chances for precipitation on Friday closer to 50 percent and may cool temperatures a few degrees into the lower 80s, at least across the NW Piedmont. && .AVIATION /12Z Saturday through Wednesday/... As of 625 AM Saturday... VFR conditions are likely at all sites through this afternoon, although MVFR conditions will begin to move into FAY then RDU/RWI starting after 21Z. Additionally, RWI is likely to see banks of dense fog for another hour or two this morning which could briefly restrict vsbys there to under 2 miles. High pressure centered well offshore continues to nose westward across NC early this morning, yielding generally light winds and mostly clear skies. A tropical depression located off the Southeast coast is expected to continue tracking to the NW toward the SC coast today, and the resulting increase in low level flow from the SE into NC will gradually pull Atlantic moisture into our area, causing clouds to thicken with lowering bases from SE to NW. FAY is expected to trend to MVFR cig/vsby after 23Z, RWI after 00Z, and RDU after 02Z as patchy light rain spreads in from the SE. Cigs/vsbys are then expected to drop to IFR very late in the forecast period, after 06Z tonight, with areas of fog and patchy precip especially at FAY/RWI/RDU. Surface winds will be initially from the south then shift to be from the SE this morning, holding under 10 kts through tonight. Looking beyond 12z early Sun morning: conditions are expected to gradually improve to MVFR by late Sun morning as cigs slowly lift with heating. As the tropical system continues to approach the SC coast, MVFR conditions will remain common through Sun with on-and- off showers, although a period of IFR or VFR conditions may occur. The tropical system is then expected to weaken as it turns and tracks northeastward off the northern SC and SE NC coast through Mon. After areas of fog and perhaps IFR stratus Sun night, VFR conditions should return Mon afternoon. A humid pattern will hold Tue/Wed with IFR fog possible each morning, but otherwise VFR conditions will dominate Tue/Wed. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield SHORT TERM...Hartfield LONG TERM...Ellis AVIATION...Hartfield

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