Area Forecast Discussion
Issued by NWS Wilmington, NC

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588 FXUS62 KILM 222240 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 640 PM EDT Thu Sep 22 2016 .SYNOPSIS...
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Weakening low pressure will drift offshore of the Carolinas through late Friday, taking the rainfall threat with it. Weak high pressure accompanied by drier air will prevail on Saturday. A modest cold front will drop south across the area early Sunday. Modest high pressure will follow and ridge across the area from the NE states through the early to mid week period of next week.
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&& .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... As of 600 PM Thursday...POPs have been increased thruout this evening with the going concern being the continued moderate to heavy rain being produced by the convection. Lightning data has been limited/sparse across the Carolinas and therefore will just mention isolated thunder thru mid-evening. With the moderate to heavy rain persisting well into this evening, unlike what the latest HRRR and RAP indicate, have updated the pcpn phraseology to include "heavy rain". In addition, with a half a dozen of Flood Advisories issued, have updated the Hazardous Weather Outlook to include the potential for temporary ponding or shallow flooding from this evenings local heavy rains. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/... As of 300 PM Thursday...Low pressure over the Cape Fear area will weaken and move east through Friday as high pressure builds down from the north. The main mid to upper trough will lift off to the north and east and a ridge builds over the southeast, although both the ECMWF and the GFS show a low cutting off from the main trough and lingering across the deep south into Sun. A weak backdoor front will make its way south through VA and into NC Sat night and should reach into SC by Sun morning. Pcp water values up close to 1.9 inches on Fri mainly aligned along the SC/NC coast will diminish to less than 1.5 inches by Sat aftn with drier air and subsidence finally scouring out the remaining moisture from this persistent remnant low from Julia. Therefore, will continue with higher pops and greatest chc of shwrs/tstms on Fri mainly east of I-95 to the coast as sfc low remains just off the tip of Cape Fear. Expect clearing to occur through late Fri into Sat as Dry air and subsidence work there way south and east as upper ridge builds east through Saturday. This should produce plenty of sunshine across much of the area, but lingering moisture along the coast should produce some cu and possibly some isolated showers mainly over the SC coast Sat aftn. Not expecting much change in the feel of the air mass with humid weather continuing. Clouds will be tough to break on Fri with continued showers and therefore expect high to be in the 70s much of the day, but places that break out in the afternoon should reach into the 80s. Saturday will warm well into the 80s with a good deal of sunshine across much of the area. Overnight lows will be in the mid 60s to around 70. && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 300 AM Thursday...A mid-and-upper level ridge axis will shift from the TN valley Sunday to the east coast by Tuesday, and will amplify between two anomalously strong upper lows into a Omega block-type pattern. At the surface, high pressure will ridge down across the mid-Atlantic states and produce onshore flow through the period. Although the primary belts of deepest moisture will remain south and west of the area, persistent onshore flow below 850 mb would provide sufficient moisture to support scattered showers. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... As of 18Z...Expect at least tempo mvfr conditions into the evening hours in scattered showers and thunderstorms. conditions are expected to deteriorate to ifr levels again tonight with a slow transition after sunrise to vfr or mvfr conditions. light, mainly northeast to east winds are expected through the taf period. EXTENDED OUTLOOK...Isolated to scattered convection, mainly during the afternoon and evening hours is possible beneath the cutoff upper low through Friday. MVFR/IFR morning stratus/fog possible each day through Saturday. Expect mainly VFR Sunday through Tuesday. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 600 PM Thursday...A relatively relaxed sfc pg will yield 10 kt or less wind speeds tonight. The progged sfc pressure field itself paints the elongated sfc low, underneath the upper low, straddling the coasts of NC and SC thru tonight. Could go variable in direction especially with speeds only at 5 to 10 kt, but instead will identify the more predominate directions, southeast to south. Significant seas will primarily be driven by a 1.5 to 2.5 foot, e to ese ground swell from distant Tropical Cyclone Karl. Latest Spectral Density Chart for 41013 indicates the ese 11-13 second period Karl swell is definitely driving the significant seas. Have increased the convection coverage this evening based on latest KLTX 88D trends. In addition, have highlighted the persistent convection over the northern-most waters oriented parallel to Cape Fear, as it pushes northward and onshore. Waterspout(s) has/have been sighted earlier today in the vicinity of this pcpn. Will mention this waterspout risk until sunset in the Hazardous Weather Outlook. SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 300 PM Thursday...Low pressure just off the tip of Cape Fear will finally move away as high pressure builds down behind through Saturday. A cold front will drop south reaching NC Sat night and should move through the waters by Sun morning. This may be fairly transparent as winds will have already shifted to the N-NE by late Fri as low weakens and shifts east. Therefore light and variable winds on Fri will become northerly by early Sat and will remain N to NE through Sat night increasing up to 15 kts. Seas 3 ft or less will increase up to 2 to 4 ft into Sat night. A longer period SE-E swell will continue through the weekend, up to 11 to 12 seconds. LONG TERM /SUNDAY THROUGH MONDAY/... As of 300 AM Thursday...Surface high pressure will build down the eastern seaboard behind a cold front, which should be crossing the waters during the day Sunday. With a blocked upper-level pattern developing through the first of the week, the surface high will persist and result in onshore flow through Monday. It does still appear that 3-4 foot swells every 10 seconds will continue into Sunday from distant tropical system Karl, falling off to a 2-3 foot wind wave by Monday.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...DCH NEAR TERM...DCH SHORT TERM...RGZ LONG TERM...CRM/RGZ AVIATION...SGL

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