Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 221519 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 1119 AM EDT Fri Sep 22 2017 .SYNOPSIS... A weak disturbance aloft will drift to the southwest today and tonight, producing isolated showers and thunderstorms mainly this afternoon. Building high pressure aloft from the north will bring dry but warm air across the Carolinas this weekend. Hurricane Maria will move northward through the Atlantic several hundred miles off the Carolina coast next week, bringing strong rip currents and large surf to the beaches, as well as hazardous marine conditions offshore. && .NEAR TERM /THROUGH TONIGHT/... As of 10 AM Friday...A few adjustments to lower POP values and sky cover in the early going and render afternoon coverage to the isolated category, as recent model trends suppress farther SW an h7-h5 cool pool. Before this happens however, diurnal heating should trip off a few showers or a storm during the early and middle afternoon, perhaps lingering into early evening over SC. No other significant changes were made. As of 300 AM Friday...Weak high pressure resides over the area this morning as an elongated trough extending from Jose down into the southeast remains in place at the mid levels. There is some dry air at the mid levels as seen on water vapor imagery moving southward. This along with a very gradual push of dry air at the surface will serve to limit convection somewhat as compared to Thursday. We are still advertising slight chance pops mainly in the South Carolina counties where better moisture remains in place. Expect slightly cooler highs today with most areas in the middle to upper 80s. Overnight lows Saturday will be slightly cooler as well by a degree or two mostly in the middle 60s. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 300 AM Friday...Deep high pressure extending from the surface up through 500 mb over the southern Great Lakes will deflect the jet stream well north of the Carolinas this weekend. An upper low developing across the FL/AL Gulf Coast have little direct impact on our weather. It is interesting to note how fortunate we are that Hurricane Maria is expected to move north along 71-72 degrees west longitude this weekend, as a track just a few degrees closer to Florida would likely get pulled westward in between the two upper level systems -- much like Hurricane Hugo did on this day back in 1989. The new 00Z ECMWF shows Maria getting awfully close to that tipping point in the steering flow...something that will need to be monitored closely. The surface pattern looks much like the upper pattern minus the upper low along the Gulf Coast. Northeasterly flow between Maria and the Great Lakes high will remain warm, but with dry out with time as a subsidence inversion develops across the area. This layer of warm air between 5000-7000 feet AGL will cap off any daytime cumulus clouds and virtually guarantee dry weather both Saturday and Sunday. 850 mb temps on Thursday were around +16C and should remain in the +15C to +16C range both Saturday and Sunday. This should provide highs 83-86 for the coastal counties and 86-89 inland. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 300 PM Thursday...A pleasant, seasonably warm and dry extended forecast in the cards, provided no surprises arise in the projected forecast track of Hurricane Maria, who is slated to pass slowly north but well offshore of the Carolinas Monday through Wednesday of next week. Aside from this, a pronounced upper ridge will dominate the synoptic pattern, providing the warm and mainly dry weather. Cross-sectional analysis through time shows exceptionally dry mid-level air through the long range period, keeping pop values very low, in the isolated to none category. The exception will be very late or just beyond the period next Friday, when a highly amplified upper trough begins to drop SE toward the East coast. This will begin to increase rain chances, while associated shear aloft begins to guide Maria off to the NE away from the Mid-Atlantic coast. && .AVIATION /15Z FRIDAY THROUGH TUESDAY/... As of 11Z...Some early morning fog exists in spots around the eastern Carolinas. In particular there is fog at LBT where visibilities have been as low as 3/4 mile recently. Morning sun should quickly burn away this fog with VFR conditions anticipated the rest of the day. Daytime cumulus should develop this afternoon with bases around 5000 feet AGL. High pressure over the Great Lakes will push drier air southwestward today and tonight. This should keep any shower activity confined to coastal South Carolina (including CRE and MYR) where the afternoon seabreeze will bring some richer maritime moisture onshore. VFR conditions this evening may decrease to MVFR/IFR again late tonight in patchy ground fog. Extended Outlook...Mainly VFR conditions through the period with the exception of possible MVFR/IFR conditions due to low clouds and fog each morning. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 1120 AM Friday...Converted small craft advisory for winds and seas to just a hazardous seas advisory as seas will exceed 6 ft long before SCA winds arrive, no other changes. Long period SE swell, or the fore-runners of distant Maria is fanning ashore although of low amplitude for now, but this will change as swell heights build. As of 300 AM Friday...Light winds fields will continue to prevail across the coastal waters through the period. With weak high pressure building in the direction through about midday will have a northerly component. Once again the sea breeze will dictate things this afternoon with southeast winds. Winds will turn back from the north once again tonight. The bigger story is the long anticipated swell from Maria is arriving. Significant seas this morning of 2-3 feet will increase by Saturday morning to 4-6 feet. Will go ahead and issue what is expected to be an extended Small Craft Advisory. SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 300 AM Friday...1020 mb high pressure centered over the southern Great Lakes will move very little this weekend. Weather conditions will be increasingly influenced by Hurricane Maria which is expected to move northward along 71-72 degrees west longitude this weekend. Although Maria`s strong winds will remain a couple of hundred miles east of the Carolina coastline, increasing wave heights (long period swells) are expected to create hazardous marine conditions all this weekend into early next week. By Sunday night seas of 5-7 feet will be common across the area, with wavelengths long enough to create shoaling and large breaking waves along the length of Frying Pan Shoals. LONG TERM /MONDAY THROUGH TUESDAY/... As of 300 PM Thursday...Unfortunately for the marine community, this period will pose treacherous wave conditions with hazardous seas nearly a certainty as Maria approaches and passes slowly north, but off the SC/NC coast. The slow movement north will bring prolonged and dangerous marine conditions, as seas build to 6-11 feet early next week, remaining elevated before a more notable subsiding trend late next week. In addition to the large waves, N winds will likely gusts to 25 KT early next week as Maria passes slowly north well offshore. This will only throw another layer of hazard on top of an existing one. The energetic, fast moving long period energy will instigate turbulence in area inlets during the outgoing tides, and will produce larger than normal breakers near sand-bars while expanding the width of the surf zone. This will require multiple days of advisories, likely initiated by the weekend. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...Coastal Flood Advisory until 1 PM EDT this afternoon for NCZ107. MARINE...Small Craft Advisory for hazardous seas from 6 AM Saturday to 6 AM EDT Tuesday for AMZ250-252-254-256. && $$ SYNOPSIS...MJC NEAR TERM...SHK/MJC SHORT TERM...TRA LONG TERM...MJC AVIATION...TRA is the U.S. government's official web portal to all federal, state and local government web resources and services.