Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 251709 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 109 PM EDT Fri May 25 2018 .SYNOPSIS... Warm and humid early summer conditions will prevail into the holiday weekend, accompanied by scattered showers and a few thunderstorms. Tropical system Alberto will move into the Gulf of Mexico Saturday, reaching the Gulf coast and stalling there much of next week, before drifting north. For the Carolinas, expect periods of rain, heavy at times, late Sunday through much of next week. With already wet ground, this may lead to problematic flooding in some areas. && .NEAR TERM /THROUGH SATURDAY/... As of 1045 AM Friday...Faint frontal boundary remains oriented east to west across SE NC and NE SC this morning, which may reveal itself a bit better in developing cu/convective fields. Low level convergence resulting from a inland advancing sea- breeze, will push the focus for showers and storms toward the NW and N through the day, nearly clearing the forecast area by 6-7 pm. While SE NC may see convection, a sharp PWAT gradient noted in MHX/CHS raobs, and also evident in low-level water vapor, will favor rain the higher coverage and intensity over NE SC. Storm motion little faster today and PWATS down a little bit, so the localized flood threat overall is more limited today. It appears the set-up is favorable for ocean showers or an isolated TSTM to brush the Cape Fear area overnight into daybreak Saturday. && .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/... As of 300 AM Friday...Western Atlantic ridge will drift a little further S and E this period. At the same time, low pressure will be deepening as it moves slowly N across the eastern and central Gulf of Mexico. Model consensus is that a tropical or perhaps a subtropical area of low pressure will be strengthening as it nears the Gulf Coast. The tropical cyclone may be located somewhere between the western FL panhandle and New Orleans early Mon morning. For the eastern Carolinas, direct impacts from this system are unlikely. However, a deep tropical flow of moisture will feed N between the Western Atlantic ridge and the developing area of low pressure, bringing widespread showers and thunderstorms and heavy rainfall. Precipitable water values will likely peak near or in excess of 2.25 inches which would be a record based on upper air information dating back to 1948 at Charleston, SC for the waning days of May. Current forecast has average rainfall amounts of 1.5 to 2.5 inches with the brunt of this falling later Sun and through Mon. Higher amounts are certainly possible. For Sat, expect the convection will be diurnally driven with the seabreeze and Piedmont trough acting as boundaries of initiation. Typically, showers or a thunderstorm will threaten the beaches during the morning through about midday and then move further inland with the seabreeze. Areas further inland should be more at risk for showers or thunderstorms during the afternoon and early eve. Moisture content of the atmosphere will be high on Sat, although not as high as later in the forecast period. Given ridging in place and the lack of upper level support, will cap POPs at chance with no POPs during the late eve and overnight. For Sun, will show convection increasing from S to N with categorical POPs overspreading the FA during the eve and overnight. We have added heavy rainfall to the gridded forecast. Given the antecedent conditions, we will be considering the need for a Flash Flood Watch with later forecast packages should our confidence in a widespread heavy rainfall event continue to increase. High temps will be in the upper 80s inland on Sat with lower to mid 80s nearer to the coast with the beaches expected to top out around 80. Lower to mid 80s should be common for highs on Sun. Lows both nights will be mainly in the muggy lower 70s with perhaps a few upper 60s thrown in across some inland areas. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 300 PM Thursday...The pattern through the extended period will remain very moist and supportive of scattered to numerous showers and thunderstorms each day. Precipitable water values in excess of 2 inches will remain through Thursday. Similar to the several days, this moist airmass will be fed by deep southerly flow between Bermuda high pressure, and a trough axis along the Mississippi River Valley extending into the Gulf of Mexico. A contributing factor will be the northward progression of a possible tropical or sub-tropical low pressure system through the Gulf of Mexico. Although direct impacts from this potential tropical system are not currently expected for our forecast area, this feature will ensure a continued feed of tropical moisture across the eastern Carolinas. && .AVIATION /17Z FRIDAY THROUGH TUESDAY/... As of 18Z...Isolated showers are occurring SW-W of KILM, and W of KMYR. Confidence is moderate to high all coastal terminals will remain VFR this afternoon. Worse case VCSH as showers should develop inland, then move away from the coast. If a tempo shower were to occur, highest confidence would be KILM. Other showers are occurring SE-S of KFLO. There is higher confidence of tempo showers with possibly an isolated thunderstorm this afternoon at KLBT/ possibly KLBT in the late afternoon. Will show tempo MVFR with VCTS in KFLO TAF early afternoon, late afternoon at KLBT. Convection slowly dissipates 01-04Z. As the night progresses tempo MVFR cigs will become possible at the coastal terminals along with possibly an isolated shower. Tempo IFR can be expected at the inland terminals. VFR expected at all terminals after 14-16z with SSW-SW winds. Extended outlook...VFR except for morning patchy MVFR/IFR in fog. Tropical moisture will be returning to the area Sun-Wed with more widespread thunderstorms with periods of IFR ceilings/visibility possible. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 1045 AM Friday...SE waves around 2 feet every 7-8 seconds will mix with light to moderate southerly chop. This regime to prevail today and overnight. Expect inshore gusts near 20 kt between 2 pm-5 pm. As of 300 AM Friday...Easterly winds of ten knots or less will continue through the morning hours across the waters. Later today sea breeze influences and a final dissipation of a residual boundary will switch winds back to the south increasing to 10-15 knots. These conditions should prevail through early Saturday. Significant seas will remain 2-3 feet. SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 300 AM Friday...Western Atlantic ridge will drift a little further S and E this period. At the same time, low pressure will be deepening as it moves slowly N across the eastern and central Gulf of Mexico. Model consensus is that a tropical or perhaps a subtropical area of low pressure will be strengthening as it nears the Gulf Coast. The tropical cyclone may be located somewhere between the western FL panhandle and New Orleans early Mon morning. For the Carolina waters, this means deteriorating marine conditions, especially Sun night and Mon. A robust seabreeze should bring wind speeds up to 15 to 20 kt Sat and Sun afternoon and eve. Seas will build from 3 to 4 ft Sat to 5 to 7 ft Sun afternoon and night. A SE swell on the order of 7 seconds will be energized later Sun and especially Sun night. Showers and thunderstorms with heavy rain are expected to become widespread Sun night and this will result in poor visibility. LONG TERM /MONDAY THROUGH TUESDAY/... As of 300 PM Thursday...Southerly flow will persist across the waters between Bermuda high pressure and a low pressure system that will be moving northward through the eastern Gulf of Mexico. Conditions will depend on how much the low is able to develop in the Gulf, but the persistent southerly fetch and strengthening gradient should support winds of 15 to 20 knots and seas of 5 to 7 feet. By Tuesday, models suggest the gradient will weaken a bit, which would allow winds to diminish to 10 to 15 knots, and seas to slowly subside. Uncertainty is higher than usual at this point, however, due to the potential for the Gulf low to develop into a tropical cyclone. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...8 NEAR TERM...MJC SHORT TERM...JDW LONG TERM...RGZ AVIATION...MRR/8

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