Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 150817 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 417 AM EDT Tue Aug 15 2017 .SYNOPSIS... Summertime heat and humidity will build and should peak Wednesday through Friday as showers and thunderstorms gradually become fewer in number. Showers and thunderstorms will be on the increase during the weekend as a cold front approaches from the north. This front may actually push to our south early next week as cooler high pressure builds from the north. && .NEAR TERM /THROUGH TONIGHT/... As of 300 AM Tuesday...A quiet early morning period with a few, mainly coastal showers and areas of fog. Deep SW flow will veer to the west aloft through this morning with continued pcp water values up at or above 2 inches. A very broad mid to upper level trough remains mainly north as models show ridging up the southeast coast in weakness between trough and Hurricane Gert well to the east riding up around ridge in the Atlantic. This ridging will weaken slightly later today as a shortwave pushes front/trough south, but should keep SC with less convection. This boundary will drop south into our local forecast area this evening with winds shifting to the W-NW behind it. By daybreak on Wed it looks like a weak boundary will be extending back along the Carolina coast, but ridging will build up into the area keeping generally quiet weather. The high res models show some iso to sct convective development into this aftn mainly associated with sea breeze, with westerly steering flow driving shwrs/tstms toward the coast and off to the east, but better chc late day as boundary drops south. Any showers or tstms that develop will drop some heavy rain as atmosphere remains very moist. The area remains in a marginal excessive rainfall outlook. Warm and humid conditions will persist with temps around 90 degrees combining with high humidity to produce heat index values between 100 and 104 most places. Some spots over Georgetown and Williamsburg counties should see heat indices up to 105, but some drier air should advect into this area enough to lower heat indices below heat advisory criteria. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 300 AM Tuesday...The period will be dominated by high heat and humidity. A Heat Advisory may be required both days for heat index values near or in excess of 105 deg. High temps will be mainly in the lower to mid 90s with near 90 at the beaches where the seabreeze should have a difficult time pushing inland given the deep WNW to NW flow just off the surface. Lows will be in the muggy mid and upper 70s. A very warm ridge of high pressure will be centered across FL and portions of the Southeast states during this period. Subsidence and warmer temps aloft should help to decrease, but not eliminate the number of showers and thunderstorms. A weak front should be all but washed out and the seabreeze looks like it will be the primary impetus for convection, especially on Wed when subsidence and warmer temps aloft will be building, but not quite as strong as on Thu. The Piedmont Trough may also act to focus showers and thunderstorms as it will be displaced further east given the flow aloft. A NW flow will become established across the area and this flow is often tricky for the Carolinas and will continue to monitor for any upstream impulses aloft which would warrant higher POPS. However, at this time, will show higher POPs Wed than on Thu, mainly scattered. Eve convection should tend to dissipate quickly with loss of heating. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 300 PM Monday...Ridge building across the Southeast late in the week will bring increasing heat and humidity before a cold front drops into the region for the wknd. Highs Friday will likely climb well into the 90s away from the beaches as 850mb temps climb above 20C, and this will combine with continued high dewpoints and humidity to produce heat index values above 100 degrees. This environment is supportive of typical aftn thunderstorms, but coverage is not forecast to be too widespread as the ridge aloft helps to minimize total convective development. Still, will carry CHC POP, focused along the typical boundaries, and any storm could produce torrential rainfall. The cold front drops into the area Saturday as a 500mb shortwave digs into the OH VLY and then shifts east through Sunday. This will push the front through the area before stalling and beginning to dissipate on Monday thanks to increasing mid-level heights again behind the departing shortwave. Showers and thunderstorms will become widespread Saturday and possibly again on Sunday before W/NW flow behind the aforementioned shortwave begins to dry the column. Temperatures and humidity will remain elevated although cooler than late week. First glance at the all-important Monday forecast is looking promising right now for the solar eclipse watchers out there. If the front can sag far enough south as currently shown by long-range guidance, the combination of surface high ridging from the OH VLY and increasingly dry W/NW flow aloft could support good viewing locally. Of course, if that front stalls overhead or begins to lift back to the north during Monday, it would create much more unsettled weather across the area. For what its worth, the 12Z/14 GFS average sky cover currently shows mostly clear sky conditions for the area Monday afternoon. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... As of 06Z...Vsbys slowly lowering across the area with areas of dense fog expected into the early morning hours, especially for KFLO and KLBT where LIFR conditions may develop. Scattered late morning and afternoon showers and thunderstorms are expected Tuesday afternoon. Extended Outlook...Scattered convection Wed through Fri, with possible MVFR to brief IFR in TSRA. Low stratus and fog during the overnight and early morning hours through the period may result in flight restrictions as well. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 300 AM Tuesday...Expect SW flow remaining around 10 kts or so, but Hurricane Gert traversing the distant Atlantic waters will produce increasing SE to Easterly longer period, up to 12 seconds, swells reaching into our waters. Have included some 4 to 5 ft seas to account for this swell, but overall seas will be lower. Winds will remain relatively light through the period with a southwesterly flow veering to a more westerly flow as a trough/front makes its way south through tonight. SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 300 AM Tuesday...Winds Wed morning may be light from the NW as trough pushes out across the waters. SW winds will return Wed afternoon, but still less than 10 kt, as a pinned seabreeze develops. Light and variable winds Wed night and Thu morning should settle on a SSE to S direction Thu afternoon, still less than 10 kt, as the seabreeze redevelops and a trough briefly tries to amplify offshore. Seas will be highest Wed morning, 2 to 3 ft with some residual 4 ft seas across portions of the outermost waters as Hurricane Gert swell decays. Seas will be 2 ft Wed night through Thu night. LONG TERM /FRIDAY THROUGH SATURDAY/... As of 300 PM Monday...A messy wave spectrum expected late week as a weak gradient exists in the vicinity of offshore high pressure. This gradient will gradually tighten beginning late Friday and on Saturday as a cold front drops into the area from the NW. Although no wind shift is expected during this period, speeds will increase, becoming SW at 10-15 kt late Friday and Saturday, after being SW less than 10 kt. Wave heights will be 2-3 ft Friday with a variety of low-amplitude wave groups comprising the spectrum. On Saturday seas will build to 3-4 ft as a SW wind wave becomes more significant. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...High Rip Current Risk from 8 AM EDT this morning through this evening for SCZ054-056. NC...High Rip Current Risk from 8 AM EDT this morning through this evening for NCZ106-108-110. MARINE...None. && $$ NEAR TERM...RGZ SHORT TERM...RJD LONG TERM...JDW AVIATION...RGZ is the U.S. government's official web portal to all federal, state and local government web resources and services.