Key MESSAGE 1, Another warm and muggy day is occuring with ridging aloft decaying across the region and a surface trough developing this afternoon across central NC. Highs are slightly cooler from previous days, but much higher dewpoints, near 80 along the coast and mid 70s inland, are bringing widespread heat indices near 105F. Heat advisory remains in effect until 8 PM for the entire CWA. As showers and thunderstorms fill in along and ahead of the sea breeze this afternoon through the evening, temps will drop with it.
KEY MESSAGE 2, An active precip pattern has set up today and persists into Wed as a series of shortwaves, inland troughing, and a very slow moving backdoor front will converge to produce higher than climo coverage of showers and storms each afternoon to early evening. Guidance continues to suggest PoPs remain around the 50-80% range each afternoon and evening. While PoP's will be higher than they have been the past several days, precip will certainly be very hit or miss across ENC, but much welcome none the less.
A change from the previous update is the addition of PoPs tonight. Scattered convection inland closer to I-95 this evening will sweep east, potentially in a linear fashion, around or after midnight. A quick burst of heavy rain is expected along it, should the line materialize. Low level inversion overnight should help prevent stronger winds from slipping down, but an isolated 20-40 mph gust is not out of the question.
Have seen PWATS jump to 2+ inches across ENC today with this very moist airmass remaining in place over the next few days. Combined with ample heating across ENC, instability will rapidly build each day with MLCAPE values generally expected to be between 2000-3000+ J/kg each afternoon. While instability will certainly be plentiful, deep layer shear will not be, as wind shear struggles to get above 25 kts. This will likely limit any significant storm organization over the next few days but cannot rule out some wet microbursts or stronger winds (40-60 mph) within the strongest storms along the aforementioned seabreeze and surface trough. Because of this, SPC has outlined a good portion of ENC in a Marginal Risk (1/5) of severe tstorms today and tomorrow. Another round of decent covg of afternoon showers/storms possible Wed as the aforementioned boundaries may still be in place. In addition to the severe threat today and tomorrow, there will also be a heavy rain threat with any thunderstorm that develops as well given the high PWAT's (2" +) and slow storm motions which could lead to some localized flooding mainly in poor drainage and urban areas. As a result WPC also has much of the area under a marginal risk for excessive rainfall over the next two days as well.
Beyond mid week, PoPs return back to climo (20-40%) as more typical seabreeze showers/storms return. Hts/thicknesses slowly build in the process as ridging begins to build once again, with heat indices 100-105 in the forecast.
KEY MESSAGE 3, Aforementioned ridging builds mid to late week into the weekend, as ensemble mean heights rise back to above normal, and forecast temps reach well into the 90s, pushing heat indices to potentially at or above 105F again as a very humid atmosphere will be in place as well. Efi for both Min/MaxTs are pushing into the 80th percentile esp late in the week.
KEY MESSAGE 4, With the aforementioned high heat and humidity expected, a very unstable atmosphere develops per med range guidance hinting at ML CAPES aoa 3.5k J/KG, and SFC based instability between 4-5k J/KG. As is typical this time of year, deep layer shear will not be too strong, but any storms that can develop with some upper level support could produce strong downdraft/microburst winds and very heavy rain characterized by PW's exceeding 2".
18z Monday through Saturday Generally VFR ceilings this afternoon, with thunderstorm coverage increasing along and out ahead of a sea breeze that is progressing inland. Have TEMPO TS mentions at all TAF sites this afternoon and evening with VCTS predominant. As we get into tonight, another round of thunderstorms is possible as a cluster or line moves west to east. Have PROB30s in the TAFs to handle this, as there is some uncertainty on how the afternoon convection influences the potential overnight convection. Any thunderstorms will be capable of producing reductions in visibility and ceilings.
Another round of fog and low stratus will once again be possible later tonight behind the convection as the area remains under a moist airmass.
Outlook (Tue through Fri): Shortwave energy tracking cross the region into midweek brings good chances for showers and thunderstorms and potential for sub-VFR conditions into Tue, possibly into Wed as well. Beyond mid week, more typical iso to widely sct activity expected as ridging rebuilds into ENC.
Steady 10-15 kt SW'rly winds with gusts up around 15-20 kts is noted across our waters this afternoon while seas along the coastal waters remain around 2-4 ft. These conditions should continue to persist today as Bermuda high remains offshore and a front slowly begins to approach. As this front begins to get a little closer tonight winds especially across the Pamlico Sound and coastal waters south of Oregon inlet should increase slightly with gusts up to 25 kts possible across the aforementioned waters. As a result have kept the SCA's up across these waters starting around 10PM tonight and persisting into Tue morning. Seas will also build to about 3-5 ft during this timeframe with some 6 ft seas possible 20+ NM away from shore.
Outlook (Tue through Fri): The gradient relaxes Tue morning with winds returning to 5-15 kt. Weakening front moves into the waters on Wed, though as is typical in July, the front appears to wash out, with any N'rly flow behind it short lived with return flow developing as early as Wed evening. Sw'rly winds look to strengthen some on Fri as a thermal trough strengthens across the area bringing our next potential threat for SCA's to the waters.
Nc, heat advisory until 8 pm EDT this evening for ncz029-044>047- 079>081-090>092-094-193>196-198-199-203>205. Marine, small craft advisory from 10 pm this evening to 8 am EDT Tuesday for amz135-156-158. Small craft advisory from midnight tonight to 8 am EDT Tuesday for amz152-154.
