textproduct: Newport/Morehead City

WHAT HAS CHANGED

A marginal risk for severe weather is now forecast for portions of the coastal plain today along the seabreeze.

KEY MESSAGES

1) Thunderstorm risk remain today with marginal severe threat on Sunday. Rainfall chances linger through the week.

2) Heat Advisory in effect south of Highway 70 today. Potential for hazardous heat remains late next week.

DISCUSSION

KEY MESSAGE 1...Biggest change for the next 24 hours was the inclusion of a marginal risk (level 1/5) for severe thunderstorms along the seabreeze today across the coastal plain from SPC. Overall general thinking remains the same with the expectation of weak wind shear (generally 25 kts or less) but impressive MLCAPE (1000-2000 J/kg) and DCAPE (above 1000 J/kg). With much less subsidence in place the seabreeze will provide the necessary lift for quick updrafts across portions of the coastal plain this afternoon. Strong downburst winds (40-60 mph), frequent lightning and heavy rain would be the primary hazard within the strongest storms this afternoon. Expect thunderstorm activity to peak between 2-10PM before waning tonight with the loss of daytime heating.

Previous discussion...Synoptic pattern continues to trend more favorably for convection across ENC this weekend and into early next week with weak front crossing the FA today and stalling to the S of the area into early next week when troughing aloft develops, opening moisture transport from the Gulf. However, this shouldn't be read as a high coverage of thunderstorms each day. Temps aloft "cool" slightly as heights aloft fall ahead of the front and the stout mid level ridge begins to weaken, and this may support at least a risk of higher coverage seabreeze convection today, particularly along the Crystal Coast where likely PoPs are mentioned. The ample moisture noted by PWATs rising to 2-2.5in, strong destabilization due to typical summer time heating and the height falls aloft poses a threat for the development of tstorms which could be strong to marginally severe. On Sunday, prefrontal trough develops around the coastal plain providing the necessary focus for shower and thunderstorm development Sun afternoon and evening. Activity likely starts off to the north and west and progresses E'wards as the afternoon wears on. With strong instability forecast to be in place and increase shear with values closer to 25-35 kts a few of these storms could become strong to severe in nature with the strongest activity likely noted along our northern tier. Damaging wind gusts would be the primary hazard within the strongest storms. SPC has the far northern section of our FA in a Slight (Level 2/5) risk of severe thunderstorms.

Early next week, higher than climo shower and storm chances are in the forecast with the greater moisture content through the column leading to PWATs in excess of 2". Additionally, deep layer shear of around 30-35kt with weak cyclogenesis along another front set to approach and stall over the area Mon may support a modest increase in the potential for organized convection, some of which could be on the strong side. The last of a series of fronts finally pushes off the coast by midweek allowing for lower precip chances outside of a daily seabreeze. We will be monitoring the approach of yet another front late next week as well.

KEY MESSAGE 2...Front today will do little to abate high temperatures and humidity, especially south of Highway 70. Although not as slam dunk as yesterday, REFS and HREF both show at least 20-30% chance of exceeding heat index values of at or above 105 in this area, and in coordination with ILM and RAH issued a Heat Advisory late this morning into the afternoon. Advisory ends at 21z with expectation of afternoon convection cooling things down.

Heat and humidity look to crank up a notch once again late next week which could bring the potential for hazardous heat indices and related health impacts. Probabilistic heat risk guidance suggests a 40-60% chance at reaching major level heat risk thresholds on Thurs/Fri. In addition to this, with the approach of a front associated with a deepening low located well to the north, breezy conditions would be possible as well if current trends hold.

AVIATION /13Z SATURDAY THROUGH WEDNESDAY/

VFR conditions in place across all terminals this morning as cold front works its way southward across the Albemarle Sound and points south. Boundary will stall just north of a EWN/ISO line this afternoon and be the focal point for shower and thunderstorm redevelopment this afternoon with highest risk focused south of the boundary. Threat will migrate northward through the evening off of convective outflow. Environment does not appear as favorable for stronger storms but torrential rainfall remains a risk which could result in brief but severe reductions in visibility. Threat will be diurnal with full convective cessation by 01-02z at the latest. Environment appears slightly better for low stratus overnight with better low-level saturation. Location of stratus development is uncertain, but signal has strengthened from previous cycle and opted to include in 12z TAFs.

Outlook: Better chances for afternoon/evening showers/storms continues through weekend with front sliding off the coast and stalling into early next week, bringing tempo reductions in vsby and/or cigs accompanying the heavier showers. Another front approaches and stalls over the area Mon leading to a wet period early next week with greater chances for sub VFR flight cats until the front clears through mid-week.

MARINE

SCA conditions diminishing this morning as weak frontal boundary migrates towards area waters. Main threat to marine interests in the near term is ongoing showers and thunderstorms, especially across the central waters where stronger convection is likely putting down periodic gusts of up to 40-50 kt. This threat will migrate southward through pre-dawn, likely expanding to zones south of Ocracoke Inlet as remnant outflow triggers more storms.

Front will continue to move through waters from north to south with 10-15 kt SW'rly winds with gusts up to 20 kts noted to the south of the front with winds shifting to a NE-E direction at 5-10 kts behind the front. This front is forecast to continue south through the day and stall just south of the area by tonight. Frontal boundary will likely be focal point for renewed convection along the Crystal Coast this afternoon which may bleed into nearshore waters. Seas hold at around 2-4 ft through the rest of the period.

Outlook (Sun through Wed): The risk of thunderstorms will increase into early next week, with best chances in the late afternoon to evening hours. SWerly flow returns Sun with another chance for more SCAs ahead of a front set to approach and then stall over ENC on Mon. This front will clear through by midweek with high pressure briefly returning thereafter.

MHX WATCHES/WARNINGS/ADVISORIES

NC...Heat Advisory until 5 PM EDT this afternoon for NCZ090>092-094- 193>195-198-199. MARINE...None.