Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 191303 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 903 AM EDT Mon Jun 19 2017 .SYNOPSIS...
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Bermuda high pressure will remain offshore this week, while a tropical disturbance moves into the Gulf of Mexico, possibly becoming a Tropical Storm by Tuesday. Moisture from the Gulf will bring periods of wet weather to the Carolinas this week. Rain may be heavy at times since the moisture is tropical in nature.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 9 AM Monday...TSTM development appears to be a given today as local sounding data indicates PW values around 2 inches right now with surface based CAPES in excess of 2000 J/kg2. Visible imagery this morning already showing enhanced cumulus fields, and paired with increasing sea breeze and Bermuda high low-level convergence, almost assures convection will erupt today. Exactly where is a tougher nut to crack but the coastal interior will see action, so will need to re-examine pop distribution for today. GOES-16 low-level water vapor channel shows a dry tongue over our western and far interior zones which may cap convection, at least initially compared to the coastal interior farther east. As of 300 AM Monday...Today will be a transitional day. Yesterday featured some mid level dry air that led to minimal convective coverage. WV imagery shows that this dry air has been pushed offshore by an approaching cold front from the NW. Meanwhile the Carolinas will start establishing a moisture tap streaming out of the Gulf and Caribbean. PW values will surge back to above 2 inches and the atmosphere will readily support precip chances given any support for ascent. That may come in the very near term along the coast with a few nocturnal showers. Through the late morning and midday hours the seabreeze will yield slightly deeper convection. Inland zones will then become favored by afternoon as usual for the time of year. Interestingly models are keeping a large part of afternoon convection west of the area near the approaching from and some channeled shear vorticity. Did not show a downward trend in POPS as this would imply but cannot rule this possibility out as there will be a narrow strip of dry air between the coastal tropical stream and the frontal moisture to our NW.
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&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 300 AM Monday...The upper air pattern for the middle portion of the week will feature a big ridge over the Southwestern U.S., the Bermuda ridge offshore, and a trough across the Great Lakes into the lower Mississippi Valley. The Carolinas will be located in the moist southwesterly flow ahead of the upper trough. The principle surface feature of note will be a tropical disturbance anticipated to become a tropical storm Tuesday as it enters the Gulf of Mexico. While many models including the 00z ECMWF take the storm into the western Gulf, the 00Z GFS is leading a smaller cluster of models that move the storm toward Louisiana beneath the trough dangling southward from the Great Lakes, perhaps implying a system will include some subtropical characteristics in the end. Deep moisture peeled off the gulf tropical system will be channeled directly across the eastern Carolinas Tuesday leading to numerous showers and t-storms. Instability should be rather small (~1000 J/kg) but with precipitable water near 2.0 inches and a snappy storm motion from the southwest at 25 mph, most areas should get rained on. Low-level convergence should be helped by a weakening cold front which will approach the area from the northwest, but likely not make it to the coast. Forecast PoPs are 70-80 percent with areal average QPF 0.50 to 0.75 inches. While moisture above 800 mb remains dense Wednesday, models suggest enough drying in the 950-850 mb layer, along with a gradual veering and slowing of the overall wind profile, that coverage of storms should be less than Tuesday. Forecast PoPs Wednesday range from 40-50 percent with QPF in the 0.1 to 0.2 inch range. Model forecast temperatures are in good agreement Tuesday, but Wednesday the GFS is a cool outlier. My Wednesday temperatures are edged up toward the NAM/ECMWF numbers with highs generally forecast to reach the mid 80s. && .LONG TERM /THURSDAY THROUGH SUNDAY/... As of 300 PM Sunday...Little of the front will remain in the vicinity Thu as Bermuda High and and 5h ridge expand over the region from the east. Despite the expanding/strengthening mid level ridge late in the week diurnal convection will remain a fixture through the period. It is worth noting the Canadian/ECMWF solutions are being favored midweek with the handling of the low in the Gulf of Mexico. The GFS has been insistent on the low tracking quickly north to the FL panhandle which then leads to an abundance of tropical moisture moving into the region early Wed and lingering well into Thu. The favored solutions eventually spread tropical moisture associated with this system into the region, but not until late in the week. This leads to increased coverage of diurnal convection Fri and Sat despite the aforementioned expansion of the 5h ridge late week. Deeper moisture exits on Sun as the 5h ridge retreats east and 5h trough approaches from the west. Enough moisture lingers Sun afternoon to support convective coverage more typical of summer in the Carolinas. Although a fair amount of cloud cover and convection is expected for much of the period temperatures will run slightly above climo during the day, a combination of starting out warmer due to morning temps well above climo, and warming under the mid level ridge. && .AVIATION /13Z MONDAY THROUGH FRIDAY/... As of 12Z...IFR fairly patchy but will plague the inland terminals nonetheless for the next 1-3 hours. Tropical streamer keeping showers in the VC of ILM but a tight moisture gradient on their west side is keeping the area VFR and will likely continue to do so this morning. Late morning into midday showers and storms will be near the coastal terminals before being pushed inland by the sea breeze. The remainder of the afternoon will see scattered thunderstorms mainly in the vicinity of of FLO and LBT. Overnight the continued increase in tropical moisture may preclude a rain-free forecast and possibly some lowered ceilings. Extended Outlook...The risk for flight restrictions due to thunderstorms will continue through the period. The probability for reduced ceilings and visibility in thunderstorms with heavy rain should be highest Tue and Wed and possibly again on Fri. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 9 AM Monday...ESE long period waves (16-17 sec) and SSE wind waves make up the spectrum this morning, with sea heights slightly bumpy at 3-4 feet. Dominant periods mainly around 6 seconds but the longer period waves may be seen as well. Marine forecast looks on track with wave heights and winds, so no major revisions needed at this time. TSTMS over land later today may edge out over the inshore waters, and a radar update today is a good idea. As of 300 AM Monday...Southwesterly flow through the period as fairly normal for the time of year. What will be not quite the norm is that wind speeds will be a bit higher than usual. The culprit: a tightening gradient between the Atlantic high and a boundary approaching from the northwest. Some weak low level jetting up to 25 kt will likely represent our gust potential late today with a little heating that may last into the overnight hours. The wind chop will run a solid 3 to 4 ft with a few 5 ft seas farther out. The 16 second SE swell is still evident in buoy data. SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 300 AM Monday...Bermuda High pressure will remain offshore Tuesday and Wednesday, providing a light to moderate southwest wind across the area. A tropical disturbance entering the southern Gulf of Mexico may become a tropical storm sometime Tuesday, but fortunately should remain too far south and west for any wind impacts in our area. Our only impact from the potential storm should be an enhanced flow of moisture aloft which may increase the number of showers and t-storms we see, particularly on Tuesday into Tuesday night. Outside of thunderstorms, seas should average 2-4 feet Tuesday and 2-3 feet Wednesday. LONG TERM /THURSDAY THROUGH FRIDAY/... As of 300 PM Sunday...The stalled front is expected to dissipate by Thu. Bermuda High will remain the dominant surface feature through the period with southwest winds 10 to 15 kt. Afternoon and evening winds could exceed 15 kt for a few hours, especially later in the period as heating leads to a slight increase in gradient. Seas 2 to 3 ft Wed will build to 2 to 4 ft Thu, eventually reaching 3 to 4 ft Fri.
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&& .ILM WATCHES/WARNINGS/ADVISORIES...
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SC...Beach Hazards Statement through this evening for SCZ054-056. NC...Beach Hazards Statement through this evening for NCZ106-108. MARINE...None.
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&& $$ SYNOPSIS...8 NEAR TERM...MBB/8 SHORT TERM...TRA LONG TERM...III AVIATION...MBB/MRR

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