Area Forecast Discussion
Issued by NWS Wilmington, NC

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863 FXUS62 KILM 231101 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 700 AM EDT Wed Aug 23 2017 .SYNOPSIS... An approaching cold front will bring increasing storms over the area late today into Thursday. Canadian high pressure will bring an early fall feel Friday and into the weekend. Breezy conditions may develop late Sunday into Monday, as a possible tropical low passes offshore and interacts with the Canadian high. && .NEAR TERM /THROUGH TONIGHT/... As of 300 AM Wednesday...Steamy high pressure offshore will contribute to another day of hot and humid conditions locally, but an air mass change is on the way later this week. Broad trough across the eastern CONUS will help drive a cold front towards the Carolinas tonight, but before this occurs Wednesday will feature hot and humid weather once again. Deep SW flow will gradually shift to westerly above the surface in response to the shifting upper trough, but surface return flow will persist. This creates a setup with WAA at the surface, and drying aloft, such that sunshine and 850mb temps around 19C will drive highs into the low to mid 90s away from the beaches today. Although dewpoints should mix out a little, at least inland, heat index values are still forecast to rise to 100-103 this aftn. Despite this heat creating a very unstable atmosphere, weak ML lapse rates and drier air aloft should limit much convection this aftn. That will change however, as a mid- level impulse and the cold front approach this evening. This impulse will help deepen the trough and push a cold front, currently across the Appalachians, slowly into the CWA. Although this is expected to happen late evening into the overnight hours, the airmass will still be quite unstable as demonstrated by 1500- 2000 J/kg MLCape on forecast soundings, and 0-6 km shear will increase to 25-30 kts, as PWATs climb back towards 2.25 inches. Best upper support does skirt north of the CWA, but SPC has placed the entire area in a MRGL risk for severe this evening and tonight. Damaging wind gusts are possible as convection tries to organize into linear sections late, but with waning instability and weakening forcing late, severe potential looks to be isolated at worst. The front will stall across the area tonight even as convection pushes offshore by Thursday morning. Cool advection lags, so mins will remain elevated tonight, mid 70s at the coast to low 70s far NW zones. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 300 AM Wednesday...A cold front will move through the area Thursday and off the coast Thursday night accompanied by scattered showers and storms. The greatest chances for rain during this period will be over the south and east. Small pops will longer along the coast Friday and south coast Friday night in NE flow as low level moisture is slow to be driven out of the area. Max temperatures will be in the mid to upper 80s both days with mins in the upper 60s to lower 70s with mid 70s at the beaches. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 300 AM Wednesday...At the surface a cold will push into the Bahamas by early Saturday with high pressure building down into the Carolinas. Saturday should be cooler and mostly dry although the easterly flow may keeps some low clouds and perhaps a light shower or two offshore around. The forecast gets interesting later in the period when the global guidance spins up what could be a tropical system along the residual front and moves it up off the southeast coast. The guidance has been showing this for a few cycles but the disclaimer of its pretty far out in time still holds. I did keep a partly to mostly cloudy forecast intact with some pops increasing especially along the coast. Temperatures will be on the cool side especially for highs more near normal for overnight lows. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... As of 11Z...Isolated showers and thunderstorms are possible coastal areas this am and along the sea breeze this aftn. More numerous showers and thunderstorms are expected to develop ahead of a cold front and affect all the terminals. Have continued VCTS with -SHRA at all terminals late this afternoon into tonight. Generally expect MVFR with SHRA but brief IFR is possible. Extended Outlook...Showers and t-storms Thursday associated with a cold front could produce localized IFR conditions. Most showers and storms will push offshore Thursday night into Friday. MVFR ceilings could linger, especially near the coast Friday. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 300 AM Wednesday...High pressure offshore and a cold front approaching from the NW will pinch the gradient today causing SW winds to increase across the waters. SW winds of 10-15 kts will slowly increase to 15-20 kts this evening and tonight, while subtly veering more to the W/SW. This increase in wind speed will allow the wind wave contribution to the wave spectrum to increase, with a 3-4 ft/4 sec SW wave topping a persistent 2-3ft/9sec SE swell. These two groups combined will produce significant seas building from 2-3 ft early, to 3-4 ft late, and at this time no cautionary statements are expected. Showers and tstms are expected across the waters late tonight as well, moving from west to east mostly after midnight, with gusty winds, lightning, and heavy rainfall. SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 300 AM Wednesday...Westerly flow of 10 to 15 KT Thursday will shift to the NE Thursday night and increase 15 to 20 kt by Friday night. Seas will build from 2 to 3 FT Thursday to 3 to 5 feet Friday night. LONG TERM /SATURDAY THROUGH SUNDAY/... As of 300 AM Wednesday...Not the best of weekend`s coming up for the marine community as high pressure will be building down into the area from the north. At the same time a front will become stationary to the south and keep the gradient elevated. For basically the entire period expect northeast winds of 15-20 knots. Seas will be elevated as well with values from 3-6 feet. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ NEAR TERM...JDW SHORT TERM...RAN LONG TERM...SHK AVIATION...JDW/RAN

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