Area Forecast Discussion
Issued by NWS Wilmington, NC

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790 FXUS62 KILM 311735 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 135 PM EDT TUE MAY 31 2016 .SYNOPSIS... Moisture associated with the remnants of Bonnie will be very slow to leave the area even as the actual system finally moves northeast of the area during Wednesday. The risk for showers and thunderstorms will persist into the weekend as a cold front drops into the area and stalls. && .NEAR TERM /THROUGH TONIGHT/... As of 1230 PM Tuesday...Quick update to account for latest radar trends. Band of heavy rainfall has setup across Cape Fear...orienting itself along an instability gradient where surface convergence is maximized. This band will likely become the primary feature to monitor this aftn as shown by most available high-res guidance as it pivots slowly across the same areas. 850mb moisture transport vectors are anti-parallel to upwind propagation vectors...suggesting training and cell regeneration as the sea breeze rotates mostly in place due to flow around the remnants of Bonnie. Have added heavy rainfall to the NE corner of the CWA and some places may receive 3-4 inches of rainfall today. Otherwise...previous discussion from 10 AM below: As of 1000 AM Tuesday...Post Tropical Storm Bonnie continues to swirl about 40 miles east of the Grand Strand this morning...and will lift very slowly NE through tonight. This will maintain the very tropical air mass in place...and forecast conditions are very similar to yesterday. While stepping outside into the near-70 degree dewpoint air may be enough to recognize how tropical the airmass is...PWAT on the 12z MHX U/A sounding was 1.81 inches -very near the all-time high of 1.87 inches for the date...a better indicator of the state of the atmosphere this morning. As Bonnie lifts slowly NE...tropical showers will rotate periodically onshore and then drop SW across the CWA. High instability and breaks in the cloudiness will permit at least isolated thunder today...but primarily expect scattered showers with periods of torrential rainfall. Timing and location of the heaviest rainfall is very uncertain...but the pattern suggests the Cape Fear region will have the best chance today and have shown the highest pop in this area. Otherwise...further S/W...less frequent and lighter rain is forecast. WPC has the area in a "SEE TEXT" for excessive rainfall today...and while localized flooding cannot be ruled out beneath any slow moving downpour...this will remain isolated at worst. Convection will be diurnally enhanced...and then wane after dark...although showers will likely persist in a much more isolated fashion through the overnight. Some fog/stratus is also expected thanks to the continued very moist column. Highs today will rise to the low 80s most of the area...although temperatures will be highly variable due to breaks of sunshine in clouds. Mins tonight will be very warm again...falling only to a degree or two either side of 70. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 300 AM Tuesday...The remnants of Bonnie may still be hanging around the the Cape Fear area into Wed as the steering flow remains weak. Atlantic ridging will build across the eastern Carolinas by Thu and this should guide the weak circulation further N and away from the area. A seabreeze is expected to develop on Wed. Low level convergence associated with this feature should allow for the development of showers and thunderstorms given the high moisture content of the air. Will still show chance pops throughout the area on Wed with likely up through the Cape Fear coast, in closest proximity to the remnants of Bonnie. A seabreeze circulation on Thu should prompt the development of more showers and some thunderstorms given a fair amount of instability and the lack of significant columnar drying. Will keep pops scattered on Thu. Expect the convection both days will shrink/wane during the night with the loss of heating. Low stratus/fog may redevelop Wed night. Highs both Wed and Thu will be in the upper 80s with lower to mid 80s at the coast due to seabreeze influences. Lows will be around 70. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 300 AM Tuesday... A cold front will drop into the central Carolinas on Friday and begin to stall. Mid level flow will be westerly and tend to provide some storm-inhibiting dry air but also possibly ample directional shear for storm cell organization as there appears to be moderate to strong instability. The front will remain overhead on Saturday and the mid level ridge appears to weaken. Saturday may thus end up a wetter day but with a diminished capacity for strong storms as widespread cloud cover dampens the diurnal temperature curve. Strong troughiness digging into the western Great Lake on Sunday could pull the front a bit to our north. This could slightly decrease storm coverage while increasing updraft intensity via stronger insolation. A cleaner passage of the front and possible legit airmass change may occur late Monday or Monday night. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... As of 18Z...The remnant low from former tropical storm Bonnie sits about 70 miles south of wilmington. Counterclockwise winds swirling around the low are pushing showers onshore. Now through about 22z the best potential for flight category impacts will exist across KCRE and KMYR where showers and t-storms are moving in from the NE. KILM could also see some impacts this afternoon although these inbound showers currently appear lighter in intensity. Farther inland...KFLO and KLBT could see a VFR cumulus ceiling with much lower chances of showers. Mainly VFR conditions should develop this evening as showers die away. New showers developing near the offshore low may rotate onshore but latest models are downplaying this potential. Beginning around 08z another low stratus cloud ceiling should develop very similarly to this morning. This should burn off between 13-14z Wednesday. Extended Outlook...Mostly VFR with mainly afternoon showers and thunderstorms. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 1000 AM Tuesday...The remnant circulation of now Post Tropical Storm Bonnie will drift slowly NE today...remaining overhead the coastal waters through the near term. The wind direction will be determined exclusively by the position of this weak low...with E/NE winds ahead of it and NW/N behind it. Fortunately the gradient is light...so wind speeds will be 10 kts or less regardless of direction...although slightly enhanced speeds are forecast within the sea breeze circulation this aftn. Seas will be 2-4 ft today and tonight...with a low amplitude wind wave and an ESE swell creating the spectrum. Scattered showers and thunderstorms are also forecast today...with periods of very heavy rainfall possible. SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 300 AM Tuesday...The remnants of Bonnie will be near the Cape Fear waters into Wed. Atlantic ridging is expected to build across the waters by Thu and this should help guide the weak circulation further NE. The seabreeze circulation will dictate wind direction and speed on Wed and Thu. Wind speeds will generally be 10 kt or less, around 10 kt Thu night. Swell energy is expected to wane slightly and this should result in 2 to 3 ft seas. LONG TERM /FRIDAY THROUGH SATURDAY/... As of 300 AM Tuesday...A decelerating cold front will approach from the northwest on Friday. Southwesterly winds ahead of this boundary will likely have a tough time much exceeding 10 kt as the areas of high pressure on either side of the boundary are quite weak. The front appears to stall just inland from the coastline on Saturday. This will continue a similar wind field as seen on Friday. The temporal persistence of the fetch may add a few 3 ft waves to outer waters. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS... NEAR TERM...JDW SHORT TERM...RJD LONG TERM...MBB AVIATION...TRA MARINE...JDW/MBB

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