Key MESSAGE 1, A plume of tropical moisture characterized by 2"+ PWATs and dewpoints in the 70s is forecast to continue to overspread the Carolinas to the east of the northward-advancing remnants of TC Isaias. At the surface, a warm front/coastal trough will trudge north along the southeastern coastline, likely with a weak, non- tropical area of low pressure developing along it. Now it appears the main axis of convection will remain over the Gulf Stream, with heavy storms offshore robbing some of the rich moisture advection into ENC. This has been a notable trend with most of the CAMs, and the 10/12Z guidance continues this trend. For this reason, have cont to trend down with QPF for the area. Most model estimates of several inches along the immediate coast, with much lower amts less than an inch or so for the interior Coastal Plain counties. Will continue Flood Watch for areas along the coast, effective through through early Sun afternoon, though bulk of widespread rain will be over by Sun morning.
KEY MESSAGE 2, Possibility of convective elements reaching the coast would warrant a tornado risk later this evening and esp overnight as the aforementioned warm front lifts through ENC. Plenty of low level helicity in place with the inc serly flow in place and strong veering wind profile downstairs. The greatest tor threat would likely be focused near the srn/sern coast where some better instability advects onshore. For Sunday, flow becomes more unidirectional with swrly low level winds ensuing during the afternoon. While helicity wanes, better instability will be in place due to daytime highs expected in the low 80s and TD's surging through the mid 70s. Will have to watch for a severe threat Sunday afternoon ahead of the cold front, with best chances appearing for the interior zones, where NCAR/HRRR svr probs are highest.
The remnants of Isaias are forecast to round the upper level ridge and move off the Northern Mid-Atlantic Coast early next week. Drier air then moves in behind it with drying conditions developing Sun night into Mon.
KEY MESSAGE 3, Strengthening onshore erly winds, building seas, and higher than normal astronomical tides may support some coastal impacts through early Mon. There remains uncertainty on the magnitude of impacts, especially given the shorter-duration of the stronger winds, as well as what should be a weaker swell and periodicity compared to the recent Nor'easter. With that in mind, there will be an increased risk of rip currents and large waves, at a minimum. High Surf Advisory remains in effect between Ocracoke and Oregon Inlets focused overnight into Sunday. Additionally, some of the most vulnerable locations along the Outer Banks may see at least some minor issues, especially with Sunday morning's high tide (7-9am). There may also be some very minor (sub advisory) coastal flooding around sounds and tidal waterways around the Crystal Coast due to the higher astronomical tides.
18z Saturday through Thursday A mix of IFR/MVFR/VFR early this afternoon should become primarily MVFR and then IFR for all locales this evening through the overnight. Periods of rain will bring vsbys down to 3-5 sm ocnl, with thunder threat mainly east of the TAF sites overnight. Nerly gradient winds through this evening with ocnl gusts to around 20 kt, somewhat higher for KMRH. The east winds will veer arond to the south late tonight and into Sun morning, though IFR will be slow to erode through the morning hours. Some thunder is possible Sun afternoon ahead of an approaching cold front, though coverage and chances will be dicated by how much cloud cover there is in the morning. More clouds will act to suppress the thunder threat.
Outlook (Mon through Thu): The shower threat will end by Sun evening as the front sweeps east and eventually off the coast later Sun night. Mostly VFR conditions will ensue for beginning to mid week as high pres builds in.
Latest obs show E winds continuing but strengthening across the waters. Speeds range from 25-35 kt south of C Lookout to 15-25 kt to the north. The stronger E winds will advect northward and spread up the NC coast with gales eventually reaching the northern waters, albeit brief, late tonight. For the sounds and rivers, SCA winds develop with these nerly pinched gradient winds though remain below gale force. Seas will peak at 7-11 ft tonight. The stronger East winds will grad weaken from south to north overnight and early Sun, gradually veering SE and then south behind the northward advancing warm front. Gales remain for the outer waters with this swrly flow through Sunday night.
For the convection threat, strong to severe thunderstorms containing waterspouts are possible tonight into early Sun morning over the Gulf Stream waters as low pres travels along a slow moving warm front. After a break in storms Sunday morning, additional showers and storms are possible later Sun afternoon into the evening ahead of a cold front, with precipitation finally clearing eastward later Sun night.
Outlook (Mon through Thu): Behind a cold front Sunday night, gusty wrly winds are expected to develop, with SCA conditions for most of the sounds and nearshore coastal waters through Monday morning. High pres eventually builds in later Mon through mid week, with winds and seas diminishing.
Nc, flood watch through Sunday afternoon for ncz047-081-092-094- 194>196-198-199-203>205. Beach hazards statement until 8 pm EDT this evening for ncz195- 196-199-203>205. High surf advisory from 8 pm this evening to 8 pm EDT Sunday for ncz204-205. Marine, small craft advisory from 5 pm this afternoon to 8 pm EDT Sunday for amz131-230-231. Small craft advisory until midnight EDT Sunday night for amz135. Small craft advisory until 2 am EDT Sunday for amz136-137. Gale warning from midnight tonight to noon EDT Sunday for amz150-180. Gale warning from 6 pm this evening to 2 am EDT Sunday for amz152-154. Gale warning until midnight EDT tonight for amz156-158-186-188. Gale warning from 6 pm this evening to 2 pm EDT Sunday for amz182-184.
