textproduct: Newport/Morehead City

WHAT HAS CHANGED

Rainfall amounts decreased slightly from 4-6" to 3-5" through Friday night.

The Heat Advisory has ended as of 7 PM.

Aviation Section Updated.

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...This evening, a cold front extends from northern VA to middle TN. Meanwhile, a mostly stationary prefrontal trough extends from the Tidewater region of VA to western NC. The prefrontal trough has been convectively active all day today thanks to a persistent SW LLJ feeding an influx of moisture into the boundary. While the LLJ is forecast to weaken some, an area of deep moisture convergence should remain in place along that trough through the night, favoring multiple rounds of convection.

Of note, a small SW to NE oriented linear convective feature has recently developed around the higher terrain of NW NC, and is moving east. The airmass downstream of this line should support a continuation across northern NC, aided by modest WAA and a continued influx of moisture within SW low-level flow. It may encounter a more deeply mixed, and more capped, airmass across central and eastern NC, but could potentially hold together in some form or fashion across the far northern reaches of ENC after sunset this evening with a gusty wind risk (40-50 mph).

Later this evening through early Thursday morning, low-level convergence should gradually shift south from VA into northern NC as the above-mentioned front and pre-frontal trough more or less merge. The front is then expected to stall across ENC during the day on Thursday, and may not push offshore until sometime on Saturday.

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 GEFS and ECMWF EFI, which show a strong signal for heavy rain over the area.

Perhaps the main complicating factor is where the strongest low- level forcing will reside as this is likely to be where the the most intense rainfall rates will occur. The latest guidance has trended towards the strongest convergence and most intense rates shifting south a bit quicker during the day Thursday, which would then setup more of a widespread moderate overrunning rainfall setup from Thursday night into Friday night. While this would still support notable rainfall totals, a faster shift south would tend to lower rainfall totals some thanks to a shorter residence time of the most intense rates. In light of this, guidance have trended down slightly with rainfall totals. This doesn't change the messaging much, but the Flood Watch will now reflect 3-5" vs 4-6". There is still some potential for a few areas to get up to 5-8" where those most intense rates last the longest.

While heavy rain and flooding is the primary risk, there may be just enough shear and instability to support a marginal severe thunderstorm risk through Friday. Deep, moist profiles should tend to favor water-loaded downdrafts, but some enhanced low- level shear may support a brief/weak tornado.

AVIATION /00Z THURSDAY THROUGH MONDAY/

A front will sag slowly south over the next 24 hours, interacting with a moist and unstable airmass, leading to an increased risk of SHRA and TSRA and low CIGs. Currently gusty winds are expected to trend lighter tonight through Thursday, gradually shifting to the north behind the aforementioned front. Reductions to VIS can be expected with the heavier SHRA and TSRA, with periods of LIFR/IFR VIS possible. The timing of SHRA and associated drops in CIG/VIS is dependent on the speed of the front. One scenario is the front parks over ENC, resulting in a prolonged period of SHRA and sub-VFR conditions from the morning through the evening Thursday. Another scenario (which is where models are currently trending) indicates a faster passage of the front. This would still bring heavy rain, but maybe for a shorter duration (a couple hours instead of the whole day), with low CIGs and more light to moderate rain setting up behind the front. Attempted to meet in the middle with this TAF issuance, while highlighting the most likely period of heavy rain with the +SHRA line.

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 into this evening in advance of a cold front approaching from the north. The front is forecast to reach the northern waters early Thursday 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 of 4-7ft this afternoon should lay down to 2-4ft by Thursday as the winds lay down. The front will be accompanied by an increased risk of thunderstorms for all waters, especially on Thursday.

Outlook (Friday through Monday): A stalled front will continue to support an increased risk of thunderstorms through Friday, although the risk should begin to decrease from north to south Thursday night, before ending across the southern waters by Friday evening. 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 from 2 AM EDT Thursday through Friday morning for NCZ029-044>047-079>081-203. Flood Watch from Thursday morning through Friday evening for NCZ090>092-094-193>196-198-199-204-205. Beach Hazards Statement until 8 PM EDT this evening for NCZ195- 196-199-204-205. MARINE...Small Craft Advisory until 2 AM EDT Thursday for AMZ131-230- 231. Small Craft Advisory until 11 AM EDT Thursday for AMZ135-152- 154-156-158. Small Craft Advisory until 5 AM EDT Thursday for AMZ136-137. Small Craft Advisory until 8 AM EDT Thursday for AMZ150.