Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 211033 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 633 AM EDT Thu Sep 21 2017 .SYNOPSIS... Weak high pressure across the Great Lakes will control our weather through the weekend. Tropical Storm Jose off the Mid- Atlantic coast should weaken, while Major Hurricane Maria will bring increasing ocean swells and strengthening rip currents to the beaches by Friday. Maria is expected to move north and remain offshore of the Carolinas Monday and Tuesday. && .NEAR TERM /THROUGH TONIGHT/... As of 300 AM Thursday...Mid level low pressure and or troughing will continue to linger across the area through the period. At the surface it will be a weak trough or convergence boundary aligned mostly inland. These features sparked a decent coverage of showers and thunderstorms Wednesday ans see no reason why the same wouldn`t today. I have increased the pops slightly for today mainly along the northern tier of counties where the best coupled forcing will reside. As for highs, I opted for the mostly warmer MET numbers which performed slightly better Wednesday. We should see a few more sites meet or eclipse the ninety degree mark. Lows Friday morning will mostly be in the upper 60s to lower 70s. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 300 AM Thursday...A convoluted upper air pattern will exist Friday and Saturday as a 500 mb high sits over the Great Lakes, while a shear zone extending southwestward from Tropical Storm Jose closes off into an upper low over southern Georgia and Alabama. The surface pattern is simpler as there is no reflection of the upper low, only the broad high pressure over the Great Lakes which remains in place through the period. In the western Atlantic, Tropical Storm Jose is expected to continue weakening and should lose its remaining tropical characteristics by Friday afternoon or evening. Hurricane Maria should turn northward near 72W longitude into the upper trough created by TS Jose. If it weren`t for Jose, the Great Lakes upper ridge would likely bridge across to the Bermuda ridge well offshore, steering Maria into the Southeastern U.S. Friday afternoon could see scattered showers and t-storms develop along the Grand Strand coast, pushing west-southwestward toward Florence and Kingstree by late in the day. Seabreeze- enhancement to low-level convergence looks to be the key for this mesoscale precipitation event which appears to be reasonably handled by the 3km NAM and RGEM models. By Saturday drier air in the northeasterly flow should make showers much more unlikely to develop. Low-level east to northeasterly winds should drop temperatures down a couple of degrees from the unseasonably warm temps of the past few days. 850 mb temps around +14C (compared to +17C Wednesday) means highs should only reach the lower 80s at the coast both days with 86-87 expected inland. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 330 PM Wednesday...If NHC Maria forecast tracks hold, the extended forecast will feature a healthy dose of warm late summer weather and mainly dry, with daytime temperatures running 2-5 degrees above normal for this time of the year. Dry air aloft remains in place of an extent that only showers are advertised in the extended period. The exception is Tuesday when we have the deepest moisture in place as Maria passes between the Carolinas and Bermuda, an outer band may fling ashore. Otherwise mainly dry and warm this period. && .AVIATION /12Z THURSDAY THROUGH MONDAY/...
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As of 12Z...A weak trough lying across the eastern Carolinas will feature broadly converging surface winds across the area today. This by itself would probably produce some towering cumulus this afternoon and maybe an isolated shower or two. However unusually cold temperatures aloft associated with an upper level trough will help produce scattered showers and thunderstorms this afternoon. Activity should begin developing around 18Z and should last through sunset. Until specific storm cells begin developing I have addressed the thunderstorm potential with VCTS/VCSH in the aviation forecasts. Light surface winds will remain generally N/NW inland, but will turn E/SE near the coast this afternoon with the seabreeze. VFR conditions are expected tonight after the day`s convection dies away, however with light winds and mainly clear skies ground fog is expected to develop late. Visibilities are currently progged to fall to 3-5 miles, however this could be dropped lower in later forecasts depending on precisely where showers and t-storms develop later today. Extended Outlook...Mainly VFR conditions through the period are expected with the exception of a few hours of early morning low clouds or fog most mornings through the period. The highest risk of IFR conditions will be in the 0900-1200Z timeframe each morning.
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&& .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 300 AM Thursday...A light south to southwest wind is currently in place across the waters. There should be a brief westerly turn to the winds later this morning before the southerly component returns later mostly driven by the sea breeze and the enhancement of the inland trough. Speeds throughout should be ten knots or less. Seas are mostly 2-3 feet and should remain so with a more significant swell component arriving just after the near term period. SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 300 AM Thursday...Weak high pressure will remain situated over the northern Mid-Atlantic states Friday through Saturday, while offshore a pair of tropical systems (Jose and Maria) swirl across the western Atlantic Ocean. For Friday and Saturday our winds will be driven primarily by the weak high, with NE-E winds around 10 knots. By Saturday evening the broad outer circulation of Hurricane Maria will begin to increase NE winds to around 15 knots. Maria`s long-period swells will impact the area well ahead of any increase in wind. Dominant wave periods around 15 seconds will slowly increase in size and could reach 6 feet as early as daybreak Saturday. Look for the issuance of Small Craft Advisories this weekend. LONG TERM /SUNDAY THROUGH MONDAY/... As of 330 PM Monday...Increasingly dangerous marine conditions this period as Maria generates large SE swell, as she moves north, east of the Bahamas. If NHC forecast tracks hold, we can expect increasing NE and N winds late Sunday and Monday but probably below Gale force through Monday. Even if winds do not become strong this period, we will still likely require a headline for large swell-heights. This will produce inlet turbulence during the outgoing tides as well, and larger than breakers near ocean sandbars, while extending the width of the surf zone. Expect seas of 6-10 feet, mainly in SE swell by late Monday. && .ILM WATCHES/WARNINGS/ADVISORIES...
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SC...None. NC...Coastal Flood Advisory from 10 AM this morning to noon EDT today for NCZ107. MARINE...None.
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&& $$ SYNOPSIS...TRA NEAR TERM...SHK SHORT TERM...TRA LONG TERM...MJC AVIATION...TRA MARINE...

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