Area Forecast Discussion
Issued by NWS Wilmington, NC

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108 FXUS62 KILM 230118 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 918 PM EDT Tue May 22 2018 .SYNOPSIS... A tropical airmass will remain across the Carolinas for the next week. A cold front approaching from the north will become a focus for better chances of showers or thunderstorms during Wednesday and Thursday. The front will dissipate Friday, with fewer showers expected into Saturday. Low pressure developing this weekend across the Gulf of Mexico will throw more moisture our way for Sunday and Monday, with substantial rain chances returning to the area. && .NEAR TERM /THROUGH WEDNESDAY/... As of 830 PM Tuesday...Diurnally driven convection has ended across the ILM CWA. The 88D echoes over the adjacent Atlantic waters are for the most part chaff. Will update to remove POPs for the rest of this evening. Based on latest Sat imagery trends, have improved sky conditions by cutting back on the clouds for the remainder of this evening and into the pre-dawn Wed hrs. This could set up a night for patchy to possibly areas of fog if the sfc winds are able to decouple. Local PWS at 1.2 this morning will rise to around 1.7 Wed morning. During the pre-dawn Wed hrs, have indicated a low chance POP, mainly along the immediate coast and waters and stretching inland by 25 miles. This the result of a weak system traversing northeast across the coastal area as it tracks northeastward...reaching the NE portions of the CWA around daybreak Wed. Have tweaked the hrly temps/dewpts and tonights lows, but with no categorical changes. Previous...................................................... As of 300 PM Tuesday...The convection that developed along the sea- breeze just before noon is now decreasing in coverage. Inland isolated convection appears to continue as the HRRR 16 UTC is not showing an increase activity this evening. So will continue with isolated showers and thunderstorm through the evening. At the surface the area will continue to be on the eastern edge of the Bermuda high and the deeper moisture is seen returning with precipitable water near 2 inches. Both the NAM and GFS are showing diurnal convection with the GFS being a bit more zealous with convection in the northwest quarter of the area. The NAM is showing less precipitation mainly west of the sea- breeze and focused over northeast South Carolina. The 12 UTC ECMWF is closer to the NAM12 solution. Lows tonight will range from the upper 60s inland to the lower 70s at the coast. Highs on Wednesday will be in the middle 80s inland and the lower 80s at the coast. && .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... As of 300 PM Tuesday...The chance for showers and thunderstorms will increase Wednesday night into Thursday as a cold front drifts south across the forecast area. The precipitable water will pool ahead and along the boundary along with marginal to moderate surface based instability. While the amount of cloud cover will ultimately impact the amount of instability any increase in cloud cover would also imply slightly cooler temperatures than what is currently forecast. For now favor a blend of MAV/MET temperatures, and POPs decreasing Thursday evening with the front drifting farther south and dissipating. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 300 PM Tuesday...A baggy upper level trough across the lower Mississippi Valley and Gulf of Mexico will become better defined Saturday and Sunday. Upper ridges building across the Pacific coast of Mexico and out over the western Atlantic between the Bahamas and Bermuda will help to spin this feature up. A surge of Caribbean moisture very similar to what we saw last weekend will be drawn northward in the deep southerly flow between this upper trough and the offshore ridge, and this could lead to another good rainfall event Sunday into Monday. The latest WPC QPF outlook for just Sunday and Monday is around 1.5 inches across our area, with forecast 7-day totals of 2-3 inches. Latest models show there will probably be some sort of low pressure development across the Gulf of Mexico late this week, but FSU cyclone phase diagrams show only the Canadian developing a significant warm core aloft. The 12z ECMWF (not currently part of the FSU website) shows the cyclone keeping a pronounced gradient in 1000-500 mb thickness above the surface low, implying subtropical characteristics at best. The GFS is the farthest east with its low pressure development across Florida on Sunday, while other guidance is westward. While not ruling out anything just yet, it`s expected the low will remain too far west for any direct impacts on the Carolinas, but enhanced southerly flow should help enhance our rainfall potential Sunday and Monday when my highest rainfall chances (50-70 percent) are currently forecast. The warmest days should be Friday and Saturday when there will be more sunshine and lower shower chances. Highs should reach the mid to upper 80s both days inland, several degrees cooler near the coast. Temperatures should top out in the lower 80s Sunday, and lower to mid 80s Monday and Tuesday. Lows in the upper 60s to lower 70s through the period are evidence of the tropical airmass we`ll have in place. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... As of 00Z...VFR through the evening hours with a moderate south southwest flow. Overnight, could see some IFR conditions, mainly with respect to ceilings. Visibilities will be MVFR as some mid cloud ceilings above the stratus will hinder fog formation. Wednesday, time height indicates fairly good moisture through 500 mbs. The LFC should be fairly low and convection should kick off around noon, with more coverage than today. Extended Outlook...The potential for MVFR/tempo IFR will increase late Wed/Thur as a cold front drops across the area and again during the weekend as tropical moisture returns. && .MARINE... NEAR TERM /THROUGH WEDNESDAY/... As of 845 PM Tuesday...Latest 88D echoes over the local waters are NOT showers or thunderstorms, they mimic aluminum chaff used by the military to evade radar tracking. Do think, showers and convection will occur, mainly during the pre-dawn Wed hrs as a weak system moves northeast along the immediate coast. The sfc ridge axis from Bermuda high pressure, will continue to extend west and onshore. This onshore placement is now south of the local waters. This has resulted with mainly a SW direction for all waters. The sfc pg will be conducive to around 10 kt or 10-15 kt wind speeds. Significant seas will run around 3 ft and will primarily be influenced by the SE ground swell that has shown some degradation during the past 12 hrs. Previous................................................... As of 300 PM Tuesday...The marine waters will continue to be under the influence of the high pressure we have seen the last few days. Winds will be southwest overnight and will shift to the south on Wednesday as the sea-breeze develops. Winds will be around 10 knots increasing to 10 to 15 knots during Wednesday. Seas will range between 2 and 3 feet through the period. SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... As of 300 PM Tuesday...Bermuda high pressure will maintain southwesterly flow across the waters Wednesday evening. However, the flow will veer to a westerly direction as a weak front drifts south across the area. The front is expected to become increasingly diffuse as it passes south of the waters allowing weak onshore flow to prevail by Thursday afternoon. Seas will be 3 ft or less through the period. Scattered showers and thunderstorms are also possible with the front in the vicinity. LONG TERM /FRIDAY THROUGH SUNDAY/... As of 300 PM Tuesday...Bermuda high pressure will remain well off the Southeast coast this weekend. By itself it would provide a gentle southerly wind and typical summertime weather. However models over the past few days have been showing the potential for a tropical or subtropical cyclone to develop across the Gulf of Mexico Friday or Saturday. The GFS is the farthest east of any model with its latest run showing a low reaching Florida on Sunday, while the ECMWF and Canadian are farther west. While it`s too early to completely rule out impacts, our latest forecast has south winds increasing to around 15 kt Sunday, with a lengthening fetch of stronger winds extending down into the Bahamas. This could build seas up toward 6 feet, assuming our wind forecast is correct. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...TRA NEAR TERM...DCH/DRH SHORT TERM...SRP LONG TERM...TRA AVIATION...DL is the U.S. government's official web portal to all federal, state and local government web resources and services.