Area Forecast Discussion
Issued by NWS Wilmington, NC

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451 FXUS62 KILM 302251 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 651 PM EDT TUE AUG 30 2016 .SYNOPSIS... Tropical Depression Eight is expected to make its closest approach to land tonight near the Outer Banks. It may become a weak tropical storm before accelerating to the ne, away from the nc mainland during Wednesday. A cold front will drop to the forecast area Friday. Its passage will be delayed until early Saturday, due to a tropical cyclone potentially affecting all or portions of the region late Thursday Night thru Friday Night. This tropical cyclone will accelerate to the NE, away from the region early Saturday. The cold front will then push through and offshore allowing dry Canadian high pressure accompanied with at or below seasonable temperatures to overspread the region during this holiday weekend. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... As of 600 PM Tuesday...Will continue with the popcorn type showers and isolated thunderstorms this evening. Looking at the KLTX 88d reflectivity, many outflow boundaries can be seen, colliding with one another resulting with additional popcorn showers...this typical of a tropical airmass. With the days heating overwith during the next 1 to 2 hrs, the convection should dissipate with the loss of the days instability. No additional forcing identified for this evening and overnight to keep POPs up over inland areas. However, along the coast mainly south of Cape Fear during the pre-dawn Wed hours, nocturnal convection may develop over the adjacent Atl waters and could push onshore given the weak progged flow from the sfc thru 7h overnight into early Wed. The near term models, RAP, HRRR and the HighresWRF are not nearly as robust in pushing pcpn activity onshore overnight like the previous several nights. The 3 models do agree on pcpn activity filling in from south to north across the FA during daylight Wed morning as a sfc trof or low and associated mid-level vort or s/w moves northward from off the GA coast. Will trend POPs upward after sunrise Wed. Previous........................................................ As of 3 PM Tuesday...Weak upper disturbance causing shallow convection to our NE and some of this activity should dot mainly the eastern third of our CWA this evening and decline in coverage after sunset. In the continued onshore flow a few showers along the immediate coast will be tough to rule out overnight especially as the remains of the Savannah low continues to fling weak vorticity centers our way. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/... As of 3 PM Tuesday...The last hurrah of the upper disturbance that sat near Savannah, GA for quite a while comes on Wednesday as the weakening system lifts northeastward. Rain should spread up the coast and may not penetrate very far inland. The extent of inland rain may hinge slightly upon how much of a surface reflection runs up the coast and where. Will cap POPS at slight far west and solid chance along the coast in deference to models like the GFS that keep just about all of the rain offshore. Rain chances should become a bit more uniform across the area on Thursday as the Atlantic moisture continues to feed into the coast and a cold front impinges upon the area from the northwest. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 3 PM Friday...Early portion of the forecast hinges upon the track and evolution of the what is currently TD 9. Guidance continues to insist on 9 moving northeast across northern FL and then moving up the southeast coast Fri into Fri night ahead of a shortwave trough dropping into the southeast. The proximity to the coast is the main concern and will determine how much impact this system has on the local area. The main concern at this point is not so much the wind but potential rainfall. As far as winds go the worst case scenario right now would be speeds in the 40 to 50 mph range. However, there could be potential for a significant amount of rain with this system regardless of its classification. Current rainfall forecast from WPC is less than 2 inches but there is likely to be a very sharp gradient given deep dry air being spread in from the west by the shortwave. If the system ends up closer to the coast there is potential for rainfall amounts more than double the current forecast which could lead to significant flooding in some areas. The remainder of the period will be dry with temperatures slightly below climo as cool, dry Canadian air mass builds over the region. Surface and mid level high pressure will ensure a quiet start to next week. Northeast flow will be continued and the guidance is trying to develop some weak coastal showers late in the period but given the abundance of dry air and possible subsidence under the mid level ridge not ready to add anything mentionable to the forecast. && .AVIATION /22Z TUESDAY THROUGH SUNDAY/... AS OF 18Z...Tropical Depression #8 is too far east for any direct impact on our weather. Tropical air hangs on across SE North Carolina (ILM and LBT) with much drier conditions being experienced across NE South Carolina. The only potential for sub-VFR conditions is in the ILM vicinity where cumulus with ceilings around 3000 feet could produce scattered showers over the remainder of the afternoon. VFR conditions should continue tonight with only a small potential of low stratus late tonight in ILM or LBT. This potential is too small for mention in the TAFs at this time. VFR will continue after daybreak Wednesday. EXTENDED OUTLOOK...Brief MVFR conditions are possible in showers Wednesday near the coast. There is uncertainty with the potential of what could become widespread MVFR conditions in rain and low ceilings near the coast Friday as a tropical storm moves well offshore. Breezy north winds could also occur. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 615 PM Tuesday...Rather noisy sfc pressure pattern and relaxed gradient to occur over the ILM waters tonight. This due to TD 8 exiting to our northeast and a sfc trof or low off the GA Coast beginning to move northeast. This will produce a variable wind direction less than 10 kt, possibly as low as 5 kt or less. In lieu of forecasting a variable wind direction, will identify or trend what directions may become. Significant seas will run 2 to 4 ft. The majority if not all of the sig. seas will be driven by the 11 to 13 second period Gaston easterly Swell...accompanied with a 1 foot or less wind chop. Showers and tstorms will be more isolated in coverage compared to the previous nights. However, by and after sunrise Wed, pcpn activity just south of the area waters will begin to spread northward due to the approaching sfc trof/low off GA coast. Previous.................................................... As of 3 PM Tuesday...Light onshore flow to continue through the period. SCEC just about to wrap up as the swell from Gaston continues to abate. Overnight seas will continue their downward trend in height. SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 3 PM Tuesday...Surface troughiness and perhaps even a weakly closed wave of low pressure to parallel the coast most of Wednesday. The strength of the low is poorly agreed upon by models and will affect the wind direction slightly though a predominant onshore flow is expected. Wind remains light on Thursday and will turn to the southwest as a cold front approaches from the northwest. Depending on the speed of TD9 the period may end in increasing winds and a turn to the southeast. SHORT TERM /FRIDAY THROUGH SUNDAY/... As of 3 PM Friday...Deteriorating conditions seem to be a given Fri morning as the system currently known as TD 9 moves across northern FL and up the southeast coast. There is still a lot of uncertainty with respect to the development, evolution, and track of the system but at the very least there is potential for strong northeast winds Fri and Fri night along with torrential rain and significantly decreased visibilities. Additionally an extended period of increasing northeast flow will build seas well above sca thresholds. So while the nature of potential headlines remains a question it is almost certain that some form of headline will be needed. The system exits northeast Sat morning with high pressure building in from the west for the remainder of the period. North to northeast flow will be maintained through Sun but with speeds under 15 kt from Sat afternoon on. Seas may remain elevated into Sat evening, warranting a SCA headline, due to continuation of northeast winds. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...High Rip Current Risk through Wednesday evening for SCZ054-056. NC...High Rip Current Risk through Wednesday evening for NCZ106-108- 110. MARINE...None. && $$ SYNOPSIS...DCH NEAR TERM...DCH/MBB SHORT TERM...MBB LONG TERM...III AVIATION...SGL

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