textproduct: Newport/Morehead City

WHAT HAS CHANGED

Aviation discussion updated. No significant changes from the previous forecast.

KEY MESSAGES

1) Multiple rounds of showers and thunderstorms expected to impact eastern NC through Friday night with a risk of flooding and a few strong to severe thunderstorms.

DISCUSSION

KEY MESSAGE 1...Frontal boundary has made little progress southward since this evening's update, currently draped across southern VA while pre-frontal trough remains largely stationary from Norfolk and Hampton Roads into the Research Triangle region. Trough axis remains very active this morning as robust LLJ of SW winds 30-40 kt continues to feed anomalously deep tropical moisture off the eastern periphery of TC Bertha over the boundary. Overall kinematics may weaken slightly tonight but not enough to prevent ongoing rounds of showers and a few thunderstorms.

The pre-frontal trough and associated low-level convergence will be slow to shift southward this morning - WoFs runs overnight point to the axis of heaviest rainfall through 12z likely sitting north of Kinston and potentially setting up across western portions of Pitt and Martin counties. If more robust convection does end up training over this corridor flash flooding could develop in the next few hours over this area.

Low-level convergence will gradually shift south from VA into northern NC later this morning as the above-mentioned front and pre- frontal trough begin to phase. The front is then expected to stall across ENC later today, and may not push offshore until sometime on Saturday. Where the front ends up stalling remains uncertain; a more progressive solution yesterday morning has now reverted back to a slower progression in the 00z suite.

A plume of anomalous, and deep, moisture is forecast to reside along the stalled frontal zone, with lift aided by periods of WAA and large-scale support from passing shortwaves. Rainfall rates will be aided by moderate instability through at least Friday, then instability begins to wane after that. The overall synoptic pattern supports periods of heavy rain and excessive rainfall rates with an accompanying risk of flooding and flash flooding. This is also supported by various forecast aids, including the ECMWF EFI, which continues to show a strong signal for heavy rain over the area through tonight.

Given the continued lack of run-to-run consistency on frontal placement and progression, where the strongest low-level forcing and thus most intense rainfall rates will occur remains a bit of a question mark. Most guidance still shows rates shifting south rather quickly this afternoon to along the southern coastline, but more members now suggest the front will hang up somewhere between New Bern and the coast with multiple rounds of convection likely hanging on through Friday. Although this would favor less severe flooding concerns to the north where overrunning rainfall would be more likely, this would increase the potential for more extreme rainfall totals of up to 5-8" along the NC24 corridor and areas north. This signal is particularly strong on Friday, where the REFS has probabilities of totals exceeding 5" of 40-50% for this very area.

Overall, guidance ultimately changed little with rainfall totals with the Flood Watch still reflecting areal average amounts of 3-5" with a risk of locally higher amounts. Areas along NC11 and west, extending northeast to the VA border remain in a Moderate (Level 3/4) risk of excessive rainfall for today while the rest of the area sits in Slight (Level 2/4). Slight risks remain for the whole area on Friday and along the southern coastline into Saturday.

A very marginal severe risk remains possible early this morning into tomorrow mainly along and north of Highway 264. Deep, moist profiles should tend to favor water- loaded downdrafts, but some enhanced low- level shear may support a brief/weak tornado.

AVIATION /12Z THURSDAY THROUGH MONDAY/

Rain beginning to encroach southward as cold front over southern Virginia continues to ease its way southward this morning. EWN has already dropped to MVFR and expect PGV and ISO to follow suit shortly within the next couple of hours. Periods of very heavy rainfall rates expected within this line, lowering vis to IFR/LIFR at times. Axis of more intense showers and storms will push towards the Crystal Coast this afternoon but overrunning precip will remain a risk for terminals to the north. Here, odds increase for IFR cigs with weaker northeasterly winds especially after 18z. South of the boundary, more prevailing MVFR is expected with a higher likelihood of experiencing intense rainfall rates. All sites trend towards IFR late tonight (likely after 04z) and lingering through the end of the period.

Outlook (Friday through Monday): A stalled front will continue to support rounds of SHRA and TSRA through Friday, with drier air trying to move in by the weekend. Sub-VFR conditions will accompany the SHRA/TSRA, with low CIGs potentially lasting into the first half of the weekend depending on how quickly the drier air moves in.

MARINE

Moderate southwesterly winds of 15-25kt will continue through this morning. The front is forecast to reach the northern waters early this morning, then stall across the central waters during the day. As the front moves in, the gradient will relax and winds will lay down to 5-15kt. Seas have slowly been trending down this morning, still hovering at around 4-6 feet but expected to ease further as frontal boundary stalls and winds collapse. The front will be accompanied by an increased risk of thunderstorms for all waters, especially today and then trending towards Onslow and Raleigh Bays Friday and potentially into Saturday.

Outlook (Friday through Monday): A stalled front will continue to support an increased risk of thunderstorms through Friday, before ending across the southern waters by Saturday. Winds are expected to be noticeably lighter along the front over the next few days. However, a more dominant northerly flow will replace the recent stretch of southwesterly flow. Within this regime, seas of 2-4ft are expected through the weekend.

MHX WATCHES/WARNINGS/ADVISORIES

NC...Flood Watch through Friday morning for NCZ029-044>047-079>081- 203. Flood Watch through Friday evening for NCZ090>092-094-193>196- 198-199-204-205. MARINE...Small Craft Advisory until 11 AM EDT this morning for AMZ135- 152-154-156-158. Small Craft Advisory until 8 AM EDT this morning for AMZ150.