Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 251135 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 735 AM EDT Fri May 25 2018 .SYNOPSIS... A front will slowly dissipate across the area today as the Bermuda ridge remains in place. The Bermuda ridge will weaken further Saturday as it shifts further south and east. Low pressure moving slowly north across the central and eastern Gulf of Mexico should be very near the northern Gulf Coast late Sunday night and Monday morning. This system will likely take on tropical characteristics and if named would be called Alberto. Deep and persistent tropical moisture will bring widespread heavy rainfall across the eastern Carolinas later in the holiday weekend. Scattered to numerous showers and thunderstorms are expected Tuesday through Thursday. && .NEAR TERM /THROUGH TONIGHT/... As of 300 AM Friday...What remains of a cold front is bisecting the area from northwest to southeast and will continue to do so this morning and through the day. Showers and thunderstorms remain a possibility, moreso along and south of the boundary, but with sufficient daytime heating areas north of the residual boundary are fair game as well. There have been some signals of showers and to some extent radar verification of showers along the coast through the morning hours. Hopefully these won`t be to the extent of Thursday morning however. Expect plenty of cloud cover for most of the day with highs in the lower to middle 80s. Most areas should be dry overnight, although some showers could wander off the ocean along coastal areas late. Lows will be in the upper 60s to around 70. && .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 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 /12Z FRIDAY THROUGH TUESDAY/...
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As of 12Z...A band of isolated showers is slowly moving N-NE and extends from KLBT-KILM to a more significant area of showers offshore. Other isolated showers are moving N in the offshore waters SE of KMYR. Except for IFR at KFLO, remaining terminals are VFR. IFR at KFLO should increase to MVFR 13-14Z then to VFR around 15Z. The coastal terminals could see tempo MVFR cigs through mid morning. Latest guidance indicates scattered showers will persist KLBT-KILM through mid morning, with additional showers developing along a resultant boundary just inland of the coast from mid morning on. Convection translates further westward to the KLBT-KFLO terminals for late morning into the afternoon. An isolated thunderstorm is possible at that time. Convection slowly dissipates 01-04Z. After midnight Z MVFR cigs become more likely at the coastal terminals with IFR at the inland terminals. The chance of showers increase, best confidence coastal terminals. Extended outlook...VFR except for morning patchy MVFR/IFR in fog. Tropical moisture will be returning to the area Sun-Tue with more widespread thunderstorms with periods of IFR ceilings/visibility possible.
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&& .MARINE... NEAR TERM /THROUGH TONIGHT/... 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. && $$ NEAR TERM...SHK SHORT TERM...RJD LONG TERM...CRM AVIATION...MRR

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