Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 240625 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 230 AM EDT Tue Apr 24 2018 .SYNOPSIS... A slow moving storm system will bring wet weather into Tuesday, along with windy conditions, dangerous surf, and coastal flooding. Easing winds and a warming trend will follow Tuesday and on Wednesday in the wake of this system. Low pressure emerging from the Gulf states will bring rain chances Thursday into Friday. Drying and seasonable temperatures are expected Saturday and into early next week. && .NEAR TERM /THROUGH TUESDAY/... As of 900 PM Monday...A Wind Advisory along the coast remains in effect through 5 am. Several beach/coastal hazards remain in effect overnight and into Tue as well. The low level jet will increase to 50+ kt down to 800 ft above the ground overnight. The strongest winds are expected within a few hours either side of 1 AM, but may linger across the Cape Fear area until mid morning Tue. These strong onshore winds will help focus moisture north of a warm front, increasing the very moist isentropic upglide. Also, given the strength of these winds just off the surface, we expect surface wind gusts to 35 to 40 mph, strongest along the coast with the beaches perhaps recording a few wind gusts to 45 mph. Bowling ball type upper low clearly evident on GOES-E WV imagery across the TN VLY is above an occluded surface low. An occluded front extends from the low towards secondary low-development in GA, from which a triple point exists with a warm front and cold front into the Atlantic Ocean and Gulf of Mexico, respectively. Ahead of this warm front, moisture is pooling and increasing across the Atlantic and cloud tops continue to cool in moisture plume just offshore. As the flow becomes strongly onshore and convergence becomes maximized, a period of potentially very heavy rainfall is likely as the plume becomes directed toward the Carolinas. Locally, the setup looks similar to October, 2015, of course that was a 4 day event and this will last 12 hours. As a warm front lifts northward, moisture will surge into the Carolinas in response to a strengthening gradient driving better moist advection onshore, and an anomalously strong LLJ of 50+ kt below 850mb surging PWATs towards 1.7 inches. These winds are forecast to reach nearly 4 standard deviations above the mean, which when combined with +2 sigma PWAT, and warm cloud depth of over 3km suggest an environment which will support very heavy rainfall. Additionally, strong diffluence, both in the mid levels, thanks to the closed nature of the low to the west, and within the LFQ of an upper jet, strong FGEN within the 850mb- 700mb layer along the warm front, and low-level convergence both along the front and due to frictional effects onshore, help drive lift and strong UVVs despite weak to no instability. As the warm front pivots NE overnight, all of these other ingredients will accompany this motion, and it is expected that a band of very heavy rainfall will lift SW to NE across the CWA overnight. While lack of instability is a mitigating factor, the other parameters all point towards widespread 1-3" of rainfall with locally higher amounts, especially closer to the coast. 12-hr FFG guidance is 5-6", so no Flash Flood Watch is needed and any minor flooding that does occur will be of the low-lying and poor drainage type. The main axis of rainfall will lift NE out of the area by late morning, and the region will briefly be within the warm sector ahead of Tuesday`s cold front which will lift NE through the afternoon. Guidance is hinting that enough forcing and residual moisture will re-spawn some showers and maybe a tstm Tuesday afternoon, but very dry air above 700mb by that time will limit the overall coverage and threat. By Tuesday evening the rainfall should be ending across the CWA. Winds will ease slowly on Tuesday, but will remain gusty through the aftn. Temps will not change much through the night and lows are expected to be in the upper 50s and lower 60s. Increasing sunshine during Tuesday and the arrival of the aftn warm sector will drive highs more typical of late April, into the mid 70s away from the coast. && .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 300 PM Monday...Upper level low pressure across the southern Appalachians Tuesday night will open up and lift northeastward Wednesday as a pair of strong shortwaves approach from the north and west. Surface low pressure will move northeastward and away from the area in tandem with the weakening upper low, allowing sunshine to return on Wednesday. Highs on Wednesday should reach the upper 70s to near 80 degrees away from the beaches. These warm temperatures in combination with dewpoints hanging in the 50s should develop a substantial field of cumulus clouds during the day. While across central and northern North Carolina colder mid-level temperatures should allow these cumulus to grow deeper and produce showers, a subsidence inversion between 7000-10000 feet AGL that becomes stronger the farther south you go should prevent showers from developing locally. I`ve got 10% PoPs across Lumberton, Elizabethtown and Wilmington during the day Wednesday but honestly expect most convective showers to remain farther north. As the departing surface low deepens as it moves from NJ into New England Wednesday night, a cold front will get a renewed shove southward and should move through the Carolinas and off the coast overnight. The atmosphere should remain stable for this frontal passage with insufficient moisture for any showers. && .LONG TERM /THURSDAY THROUGH MONDAY/... As of 300 PM Monday...Another area of low pressure may bring showers to the area Thursday into Friday. Otherwise, the long term looks dry with temperatures near or slightly below seasonal normals. Normals for this time of year run mid to upper 70s by day and mid 50s overnight. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... As of 06Z...Widespread MVFR and IFR likely into mid-morning. Very heavy rain and possibly an isolated thunderstorm will occur generally through 07-10Z, possibly through 12Z at KILM/KLBT. Easterly winds will be quite strong with gusts 25 to 30 kt possible. As winds veer to the southeast this morning, speeds will decrease. Southeast winds should become south around midday while MVFR/IFR cigs should improve to VFR 16-18Z. Extended outlook...Tempo MVFR Thu night through Fri night. Otherwise VFR. && .MARINE... NEAR TERM /THROUGH TUESDAY/... As of 900 PM Monday...A Gale Warning is in effect. Dangerous marine conditions overnight into Tue as strong low pressure and its associated frontal system impacts the waters. Surface low across GA will lift NE overnight into Tuesday, while high pressure near New England slowly retreats. The gradient between these two features will produce a pinched gradient, resulting in wind speeds of 20 to 30 kt with gusts to around 40 kt. Seas will peak in the 8 to 12 ft range and as high as 13 or 14 ft. The wind direction overnight will be SE. Widespread showers and a few thunderstorms into Tue morning will result in poor visibility due to heavy rain. During Tuesday conditions will slowly improve with winds veering from SE to SW by the end of the period as the cold front lifts across the waters. During this wind shift speeds will gradually lower as well, becoming 15-20 kt with higher gusts. A Small Craft Advisory will be required once the Gale has eased. Seas will be subsiding during Tue, lastly across the northern waters. Seas may not drop below 6 ft until late Tue night or on Wed. The wave period will remain around 9 seconds. SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 300 PM Monday...Low pressure centered near Raleigh Tuesday evening should drift northeastward across the Chesapeake Bay Wednesday morning, then into New England Wednesday night. A cold front behind the low will initially be very slow to move south, but should get a renewed kick Wednesday night as the low deepens. Compared to winds coming up tonight and Tuesday, winds Tuesday night through Wednesday night should be a piece of cake: 15 knots from the southwest Tuesday evening, then around 15 knots again with the seabreeze on Wednesday afternoon. Wind directions should veer northerly by late Wednesday night as the cold front moves across the area. Despite diminishing wind speeds, large seas will remain with us through at least Wednesday morning, a consequence of the storminess along the Southeast coast today through Tuesday. Nine-second southeast swell as large as 8 feet will move through the coastal waters Tuesday evening before diminishing to 3-6 feet Wednesday morning. We`ll likely need to keep a Small Craft Advisory running through Wednesday morning. LONG TERM /THURSDAY THROUGH SATURDAY/... As of 300 PM Monday...Expect shifting winds over the waters Thursday and Thursday night with low pressure moving through. NE winds Thu AM will become SE by Thu night and SW on Friday. Speeds currently look to run about 15 KT but this could change depending on how this next low progresses. W to SW winds of 10 to 15 KT are expected for the remainder of the period. Seas of 3 to 4 FT THU will subside to 2 to 3 FT Friday and Saturday. && .TIDES/COASTAL FLOODING... As of 900 PM Monday...A Coastal Flood Advisory is in effect for minor coastal flooding around the time of high tide, both at the beaches and for portions of the lower Cape Fear River to include downtown Wilmington. Given the duration and overnight increase in strength of the onshore winds as well as the increasing rainfall rates, decided to go above the available tidal predictions. We are expecting tidal departures on the order of 1 to 1.5 ft and as much as 2 ft. Departures of this magnitude would bring a brief period of minor coastal flooding to the beaches around 300 AM and downtown Wilmington around 530 AM. Significant beach erosion is possible with the overnight high tide as well. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...Wind Advisory until 5 AM EDT early this morning for SCZ054>056- 058-059. Coastal Flood Advisory until 5 AM EDT early this morning for SCZ054-056. High Rip Current Risk until 6 AM EDT early this morning for SCZ054-056. NC...Wind Advisory until 5 AM EDT early this morning for NCZ105>110. High Rip Current Risk through this evening for NCZ106-108-110. Coastal Flood Advisory until 5 AM EDT early this morning for NCZ106-108-110. Coastal Flood Advisory until 8 AM EDT this morning for NCZ107. Beach Hazards Statement until 6 AM EDT early this morning for NCZ110. MARINE...Gale Warning until noon EDT today for AMZ250-252-254-256. && $$ NEAR TERM...RJD/JDW SHORT TERM...TRA LONG TERM...RAN AVIATION...III TIDES/COASTAL FLOODING...RJD

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