Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 231056 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 656 AM EDT Fri Sep 23 2016 .SYNOPSIS... Weak low pressure will circulate near the South Carolina coast today. The low will drift offshore Saturday and allow high pressure and drier air to build in. A modest cold front will drop south across the area Sunday, followed by high pressure through Monday. Rain chances will increase by midweek ahead of another cold front. && .NEAR TERM /THROUGH TONIGHT/... As of 700 AM Friday...Low pressure aloft has opened up since Thu, but general troffiness will linger across the area through the period. Low pressure at the surface still appears stuck across Williamsburg and Georgetown counties this morning. Weak surface low should continue to be nudged ENE through Saturday morning. This will mean another day of unsettled weather with the potential for significant rainfall given the abnormally high precipitable water values. These values will be dropping below 2 inches inland, but remaining near or just above 2 inches along the coast through the day. We are watching another plume of tropical moisture working its way northward along the southeast coast. This deep moisture could again enhance rainfall rates across mainly our coastal areas. We will continue to access whether a Flash Flood Watch is warranted for a small portion of the area later today. Will carry scattered to numerous showers and some thunderstorms with heavy rain. Coastal areas should again see the heaviest rainfall amounts. Generally we are expecting one quarter to three quarters of an inch of rain. However, these amounts could be easily quadrupled in areas where convection repeatedly redevelops with the risk for excessive rainfall, given the antecedent conditions, highest along the more immediate coast POPs will be trending down, lastly along the coast by/during the eve as drier air begins to seep into the area. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 300 AM Friday...Some of the drier air seen on water vapor imagery should be able to work its way into the area by Sat. However, there still will be some troffiness across the area. A backdoor cold front will approach from the N Sat night and should move across the forecast area during Sun. Will keep POPs largely below threshold on Sat with a small POP across southern areas where moisture will be slightly greater. Then will include a small POP for Sun with the front moving across the area. Precipitable water values will be dropping through the period resulting in much lower rainfall rates and we are not expecting significant rainfall during the weekend. More sunshine on Sat should bring highs to the mid and upper 80s. Highs on Sun will still be above normal, lower to mid 80s. Lows will be in the upper 60s to lower 70s Sat night and mid and upper 60s Sun night with near 70 at the beaches. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 300 AM Friday...A mid and upper level ridge axis will transition over the area Monday, ahead of a deep upper low that will be dropping across the Great Lakes. Surface high pressure build in from the north on Monday but shift offshore Tuesday. This will result in an increase of moisture off the Atlantic as winds become southeast, and expect rain chances to increase Tuesday and Wednesday ahead of a cold front which is expected to move off the coast by early Thursday. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... As of 12Z...A surface low is S of KMYR with a weak trough along the coast. Flight conditions will be a general repeat of the previous 24 hours. There is high confidence LIFR will lift to 14-15Z, after which MVFR will occur most of the morning. Cigs will improve to VFR by this afternoon outside of precipitation. Precipitation is currently curring in widely scattered bands rotating slowly around low pressure to the south. Satellite picture suggest enhanced clouds not as prevalent as yesterday morning so this mornings precipitation may be less. Convection will increase as the afternoon approaches along the coast and in bands rotating around the low. Confidence is low as to where exactly bands of precipitation will set up. If a band sets up directly over a terminal there could be an extended period of SHRA/IFR/VCTS. Due to low confidence of timing this is not indicated in TAFs. Have included TEMPO groups indicating MVFR and will amd as precipiation develops as necessary for IFR. Models suggest the surface low will fill and weak high pressure will build into the terminals overnight. With moist low levels, light winds and sct skies there is increasing confidence of dense fog development. EXTENDED OUTLOOK...MVFR/IFR stratus/fog possible late Friday night and Saturday morning. Expect mainly VFR Sunday and Monday, but chances for showers and tstms will begin to increase Tuesday and Wednesday. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 700 AM Friday...Weak low pressure will remain in the area and this will keep wind speeds under 10 kt through the period. The wind direction will vary depending on the position of low pressure. The wind direction tonight will be mainly from the N. Seas will be 2 to 3 ft, but near 4 ft out around Frying pan Shoals due to the 11 to 12 second easterly swell generated ahead of distant Tropical Storm Karl. SHORT TERM /Saturday FRIDAY THROUGH SATURDAY NIGHT/... As of 300 AM Friday...Weak surface low pressure should move further offshore. A backdoor cold front will move across the waters on Sun. The strongest wind speeds this period will be in the wake of the front, Sun and Sun night. Winds speeds will be up to 15 to 20 kt, otherwise sustained winds will be 10 to 15 kt. The wind direction will be mainly NE, becoming ENE Sun night. Seas will build to 4 to 5 ft Sun and Sun night as a robust easterly swell remains. LONG TERM /MONDAY THROUGH TUESDAY/... As of 300 AM Friday...The period will begin with northeast flow as high pressure ridges in behind Sundays cold frontal passage. As the high transitions off the mid-Atlantic coast Monday afternoon, winds will veer to the east, then south behind an inverted trough that will lift north across the waters Tuesday. Onshore flow and a moderate pressure gradient will support 15 knots of wind and 3-4 ft seas on Monday, and the continued onshore trajectory Tuesday should see seas build to 4 ft throughout, with perhaps some 5 footers in the vicinity of Frying Pan Shoals, and near 20 nm out. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ NEAR TERM...RJD SHORT TERM...RJD LONG TERM...CRM AVIATION...MRR

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