Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 140735 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 335 AM EDT Mon May 14 2018 .SYNOPSIS...
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Today should be the last day of hot inland temperatures for awhile. Low pressure developing off the Florida west coast should push tropical moisture over the Carolinas beginning Tuesday. This will lead to more clouds, increased rain chances, and cooler daytime temperatures. This weather pattern should last into the coming weekend.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 300 AM Monday...Low pressure attempting to organize in the Gulf of Mexico will throw increasing clouds and moisture into the Carolinas, but today should be a nice day - the last one for quite some time according to latest forecast guidance. GOES-E satellite imagery early this morning shows a dense cirrus shield across the Southeast arcing from the Outer Banks SW into the panhandle of Florida. This looks very much like an anti-cyclonic cirrus shield atop a tropical system, mentioned by each forecaster on shift tonight, and is in response to ventilation atop a 30% special TWO area in the GOM. This cloud cover combined with low- level winds of 25-35kts on the latest LTX VWP will inhibit any fog through morning, but some stratus is possible nearer the coast where low-level moisture is higher. This will keep mins elevated through daybreak, and have raised forecast lows a bit, suggesting the most humid lows so far of this late spring. Although the Bermuda ridge which has been responsible for the hot temperatures the past few days will persist today, in addition to mid-level ridging atop the lowered heights in the Gulf, cloud cover will be much more significant than the past few days which will keep temps several degrees cooler this aftn. Highs today are forecast to climb into the mid 80s near the coast, to around 90-92 well inland, still well above climo for the date. A strong sea breeze will keep the beaches to around 80 and with the synoptic flow S/SW, the sea breeze should penetrate well inland by this evening. Forecast soundings and time-height profiles show moisture increasing both from cirrus level down this evening, as well as in the lower levels as deep southerly flow advects tropical moisture from the Gulf and Atlantic. PWATs are forecast to climb to 1.75-2.00 inches by daybreak Tuesday, approaching +3 SD`s from normal. This suggests that showers will overspread the area from south to north overnight, and have raised POP to mid-chc SC and SCHC far northern zones. There remains some discrepancy into how far showers will reach north by the end of the period as they need to overcome some significant dry air. Latest ECM slowed precip onset until well into Tuesday, but GFS/NAM and most of the SREF plumes have QPF at or just before 8am Tuesday. The nature of this activity will likely be scattered showers with embedded heavy tropical downpours, and have also included a SCHC of TRW- after 4am when lapse rates become nearly uniformly moist adiabatic into the charge separation zone. QPF is forecast to be minimal during the near term despite increasing POP, but again, this will be the beginning of an active week. Dense cloud cover and warm southerly winds will keep mins elevated once again tonight, falling only into the upper 60s to around 70.
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&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
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As of 300 AM Monday...Weak surface low pressure has developed beneath an upper level low across the northeastern Gulf of Mexico. Various models over the past several days have showed a shallow warm core developing with this system, and NHC continues to monitor this system for tropical or subtropical development. Regardless of how it may eventually develop, this low should remain too far south and west of the Carolinas for any direct impacts, however deep tropical moisture being drawn northward from the Caribbean along the east side of the circulation should lead to an marked increase in showers and thunderstorms over the next few days. Precipitable water values should rise to 1.75 to 1.90 inches, and any hints of a capping inversion aloft should erode Tuesday morning. The GFS remains the fastest model to bring deep moisture and precip into the area, and the spread between it and slower ECMWF has not really closed over the past 24 hours. I would prefer a slower onset of precip Tuesday morning, but have 20-30 PoPs forecast at daybreak as far north as LBT and ILM for continuity with other NWS office forecasts. Despite considerable cloud cover, there should still be a diurnal component to the upcoming convection. Daytime PoPs Tuesday will range from 50 percent across the Cape Fear area to 80 percent along the Santee River into Kingstree and Lake City. Wednesday`s daytime PoPs are 60-70 percent, highest inland. Nighttime PoPs are generally 20 percent lower across the board. Despite high PWs, CAPE 500 to 1000 J/kg, and modest unidirectional winds in all model forecast soundings, the NAM is really the only model showing an explicit signal for heavy rainfall, and that is mainly west of our forecast area. Diurnal temperature ranges will become constricted by the increase in clouds. Highs both days should reach 80-85 degrees with nighttime lows in the upper 60s to around 70.
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&& .LONG TERM /THURSDAY THROUGH SUNDAY/... As of 345 PM Sunday...Medium range guidance continues to show a very slow moving and in reality in the first part of the extended a blocking pattern. This features a trough or essentially a broad weakness over the southeast with a rex type configuration out west. The pattern remains in place until the weekend into early next week a shortwave ejecting from the west attempts to push everything eastward. Overall pops remain high through the period with a trend of decreasing slightly in time and of a diurnal nature. The temperature forecast changes very little as would be expected with daytime highs mostly in the lower to middle 80s and overnight lows in the middle to upper 60s. && .AVIATION /06Z MONDAY THROUGH FRIDAY/... As of 06Z...High confidence in VFR through much of the valid period after a small chance for some stratus overnight near the coast. Expansive bermuda-type high pressure offshore will remain the dominant feature producing light southerly winds overnight of 4-8 kts. Despite a mostly dry column and this weak moist advection, fog is unlikely anywhere due to both ample cirrus aloft and VWP winds of 25-35 kts below 2 kft. However, guidance does continue to show some stratus potential near the coast where near-surface moisture is higher, and have indicated some SCT at IFR level for ILM/MYR/CRE late tonight into early Monday. Confidence is low in any cig restriction however. Any stratus will lift Monday morning and some aftn Cu/StratoCu is expected at 4-6 kft, potentially producing brief VFR cigs inland. Widespread high level cirrus will persist all day as well. Winds will remain from the S/SW at all terminals, with gusts 15-20 kts expected at the coast within the sea breeze during the aftn/eve. Otherwise, expect wind speeds around 10 kts. Showers will be encroaching on the area late, but attm any restrictions are expected to hold off until just beyond this TAF issuance period. Extended Outlook...Tropical moisture will be in store through the extended. Periods of MVFR or lower cigs/vsbys will be increasingly likely from Tue-Fri mainly associated with scattered to numerous showers/thunderstorms. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 300 AM Monday...Low amplitude seas will persist much of this period although slow amplification late is forecast. Latest buoy obs show seas of just 1-3 ft across the coastal waters, with a dominant period of around 8 sec due to light winds and a pronounced SE swell. This swell will remain dominant in the spectrum into this evening thanks to SW winds remaining 10 kts or less outside of the near shore sea breeze. This evening and through tonight, winds will increase to 10-15 kts, which will allow a shorter period 5-6 sec southerly wind wave to amplify in conjunction with slow deamplification of the SE swell. This wind wave will grow to 3-4 ft, causing significant seas to grow to 3-4 ft overnight and into Tuesday morning. SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 300 AM Monday...Low pressure in the northeast Gulf of Mexico will slowly drift northward, approaching the Florida Panhandle and Alabama coastline Wednesday night. Southerly winds will continue across the Carolina coastal waters through the period in the pressure gradient between this low and Bermuda high pressure well offshore. This southerly fetch sustained for several days should begin to build a 6-second wave set which could reach 4-5 feet in height by Wednesday night. A side effect of the southerly wind will be an influx of tropical moisture which should increase the potential for showers and thunderstorms through the period. LONG TERM /THURSDAY THROUGH FRIDAY/... As of 345 PM Sunday...Consistent pattern for the extended marine forecast as the synoptic pattern changes very little. Overall expect winds mainly from the south in a range of 10-15 knots with a daytime acceleration near shore due to the sea breeze. Winds may be slightly higher very late in the period as in leaning toward the higher end of the range due to increased low level jetting. Significant seas should be 2-4 feet possibly increasing very late in the period with the increased winds and more of a swell component developing with the persistent fetch.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...TRA NEAR TERM...JDW SHORT TERM...TRA LONG TERM...SHK AVIATION...JDW

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