Area Forecast Discussion
Issued by NWS Wilmington, NC

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521 FXUS62 KILM 211103 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 703 AM EDT Mon Aug 21 2017 .SYNOPSIS... A weak and stalled front will slowly dissipate to just a trof of low pressure today. Moisture from an upper trof to our south will make its way onshore and inland during today. High pressure will expand across the area from the western Atlantic late today thru early Wednesday, allowing the heat and high humidity to continue. A modest cold front pushing southeast will track across the Eastern Carolinas late Wednesday night thru Thursday. Models indicate this front to continue south and east of the area before stalling on Fri. This will enable Canadian high pressure to build in behind the front bringing drier weather and slightly below normal temps for the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 330 AM Monday...Isolated scattered showers offshore will migrate towards shore through the early morning hours, and potentially bring light precip amounts to the nearshore zones in the predawn hours. Also anticipate very good potential for fog to develop towards daybreak, given similar low-level moisture profile as last couple of days, and even lighter winds in the lowest few thousand feet. Abundant low-level moisture and instability should allow for the development of widely scattered showers and thunderstorms by midday, primarily along the sea breeze and the remnants of frontal boundary lying across the southern CWA. Convection will fade with the loss of heating after sunset. High temps will range from the upper 80s coast to the mid 90s across the Pee Dee, and this will lead to heat indices topping out in the low 100s. As far as sky cover for eclipse viewing, time-height cross sections do indicate some mid-level dry air, however a blanket of moisture around 200 mb will likely result in a filtered view through thin cirrus at best. More than likely, any potential glimpse would have to come between cumulus buildups, which are expected to begin by late morning. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 330 AM Monday...Western Atlantic ridging sfc and aloft will dominate the FA`s weather Tue. Weak inverted mid-level troffing extending from the Gulf of Mexico northeastward across eastern Georgia and the eastern Carolinas. This troffing apparently broke off from the upper low that pushed westward across the Gulf of Mexico to near the TX and Mexico coast at the start of the short term period. The dynamics associated with this upper trof will combine with the sea breeze and a sfc trof, which was once a stalled frontal boundary, and produce a round of convection. Will indicate chance POPs but may need to be upped especially with various model Mos Guidance not very enthusiastic with shower and thunderstorm activity during Tue. For Wednesday, the upper ridging associated with the Western Atlantic High, is progged to get shunted southward as the upper troffing amplifies and expands southward across the Eastern 1/3rd of the U.S. This will push a sfc cold front southeastward, reaching the front doorsteps of the ILM CWA by Thu morning. Will indicate increasing POPs during Wednesday and continuing that trend thru Wed night with a POP peak in the high chance category. Will need to monitor late Wed into Thu for possible severe thunderstorm activity given the decent dynamics involved. Daily max/min temps will remain slightly hier than the norm for this time of the year, thus continuing with the heat and high humidity. && .LONG TERM /THURSDAY THROUGH SUNDAY/... As of 3 PM Sunday...Primary feature influencing extended forecasts is cold frontal passage early Thursday. This is supported by GFS/ECMWF upper patterns, both of which also migrate Canadian High pressure into the region Friday through the weekend, imparting a slightly drier and cooler feel than late. GOES-16 shows the circulation near 20N north of Puerto Rico, which may fester off the FL coast near a stalled boundary early next week, potentially deepening. Regardless of intensity, the expectation is this feature will lift to the north slowly, remaining offshore of our coast. A few strong storms are possible early Thursday as wind shear aloft and low- level convergence increase as the upper trough edges in. && .AVIATION /10Z MONDAY THROUGH FRIDAY/...
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As of 12Z...VFR conditions to prevail after the MVFR, IFR and even LIFR conditions from the early morning fog. The upper trof off the Carolina coasts, will swing onshore this aftn and evening. Convective tropical type showers will increase in coverage this morning and eventually increase in strength and transition to thunderstorms once the days heating commences. Have indicated VCSH and VCTS for the coastal terminals but may eventually need TEMPO groupings. Various model MOS Guidance keeps POPs rather low if not altogether out of the fcst. Obviously, they are not verifying too well given the latest mosaic radar coverage along the coast. The activity will likely weaken and dissipate quickly after sunset, followed by nocturnal shra/tsra development over the adjacent Atl waters during the predawn Tue hrs. Have again indicated MVFR fog in the 08-12z Tue time frame with later TAF forecasts providing more detail. Winds generally calm early, will become E to SE at 5 to 10 kt by late morning and veer slightly to the SE to S 5 to 10 kt, except 10 to 15 kt across the coastal terminals, this aftn and early evening. Winds will likely again decouple around or taking up to several hours after sunset. Extended Outlook...Diurnal showers/tstms expected Wednesday afternoon, becoming more numerous Wednesday night and Thursday with fropa. Convective potential will decrease Friday as the front moves south of the area.
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&& .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 330 AM Monday...Isolated showers over the waters will migrate northward through the predawn hours. Potential for widely scattered showers and thunderstorms will continue over the waters through the period, although they should be dampened out a bit during the daytime hours once the sea breeze circulation develops. Winds will remain light and variable in a weak pressure field, with seas around 2 ft. Models continue to show a 2 ft 9 second swell moving into the waters late tonight. SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 330 AM Monday...Winds and sea conditions will start out somewhat benign given the relaxed sfc pg and a weak sfc pressure pattern. This will change by late Tue thru the remainder of this period. The sfc pg will begin to tighten along with an organizing sfc pressure pattern that will both yield increasing SW winds. The significant seas will initially be driven by an ESE-SE 1 to 2 foot ground swell at 10 second periods initially, that will build to 2 to possibly 3 feet late Tue thru much of Wed. This ground swell will dominate the seas spectrum thruout this period with wind waves helping to push significant seas to a 2 to 4 foot range during Wed. Will need to be cognizant of any convection that pushes off the NC and SC mainlands this period, and especially late this period when thunderstorm activity becomes better organized and potentially stronger. LONG TERM /THURSDAY THROUGH FRIDAY/... As of 300 PM Sunday...The extended marine period will become a bit bumpy ahead and after a cold frontal passage on Thursday. A wind shift will migrate across the 0- 20 NM waters early Thursday. Strong Canadian high pressure will interact with the front offshore to produce NE winds 15-20 KT Thursday into Friday. As a result, `Caution` and even `Advisory` headlines are possible this period. Seas of 3-5 feet can be expected Wednesday afternoon through much of Friday before subsiding, and up to 6 feet well offshore. A few storms may be strong Wednesday night through Thursday as a cold front crosses the waters and radar updates are encouraged. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...DCH NEAR TERM...CRM SHORT TERM...DCH LONG TERM...MJC AVIATION...DCH

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