Swell Matrix

Area Forecast Discussion

National Weather Service Newport/Morehead City Nc

700 am EDT Tue jul 17 2018

Synopsis

High pressure will remain offshore through today. A cold front will move in from the northwest tonight and push through the region Wednesday. The front will remain stalled south of the area through late week, then lift back north this weekend.

Near Term

Through today As of 7 AM Tue, Main change with AM update was to decrease pops through this morning, as little activity observed upstream. Still expecting sct to numerous coverage of shra/ts this afternoon, mainly away from immediate coast.

Previous discussion, As of 345 AM Tue, Lingering shra/ts near along the OBX early this morning in association with weak sfc low tracking up along the NC coast will move east and offshore before daybreak. Meanwhile, area of convection approaching the southern coastal waters from Cape Fear to the south may impact downeast Carteret before sunrise.

A broad upper trough, shortwave energy and sfc cold front will approach the area today. Scattered to numerous showers and storms are expected today. Best chances still appear to be along the coast during the first part of the day with convection moving off the water, then coverage likely transitioning inland during the afternoon hours as sfc convergence increases and daytime heating occurs. Forecast soundings continue to show CAPES increasing to 2500-3000 J/kg and bulk shear 10-20 kt. Some stronger storms will be possible in the afternoon and evening hours, but at this time it looks like the main threat will be heavy rain with the potential for localized flooding. Wpc has the area outlooked in a Slight Risk to Marginal risk of Excessive Rainfall. Expect PWAT values 2-2.3 inches. Low level thickness values, cloudy skies and SW flow support highs 85-90 degrees though TD's will be quite high in the mid 70s, so uncomfortable heat indices approaching 100 degrees.

Short Term

Wednesday As of 345 AM Tue, There may be a break in the convection early this evening, though cold front will enter from the west later in the evening through the overnight and bring more numerous thunderstorms through E NC. Best chances for shra/ts will be the coastal areas late at night through sunrise as the front exits the coastal plain. Again, could see periods of heavy rain rates with localized flooding from storms as PW's will remain above 2 inches.

Long Term

Wednesday through Monday As of 350 AM Tuesday, A cold front will cross the region early Wednesday followed by high pressure on Thursday and Friday. Expect unsettled conditions for the weekend into early next week with increased chances for showers and thunderstorms.

Wednesday/Wednesday Night, A broad trough aloft will move through the Northeastern U.S. While a cold front moves through the region early in the day. Guidance suggests a big gradient between northern and southern zones, and have slightly lowered PoPs for far northern zones as a result, while maintaining high chance to likely PoPs for the southern zones/waters. The front will serve as the main forcing mechanism for showers and thunderstorms. Instability will be plentiful and PWATs build back above 2 inches late Tuesday into Wednesday. Shear will be the limiting factor for organized severe storms. Biggest threats from any isolated severe storms are hail, damaging wind gust, and localized heavy rainfall. Temperatures will range mid to upper 80s, with lows in the upper 60s to low 70s.

Thursday and Friday, The upper trough over the NE U.S. Will lift northeast into the Canadian Maritimes while another trough digs into the upper Plains, with brief ridging between these two features moving east through the Mid-Atlantic States during this period. Broad high pressure at the surface will shift from the southern Great Lakes through PA/NY and off the southern New England coast, helping keep Thursday and most of Friday dry for Eastern NC. Guidance is in fairly good agreement with a weak surface low forming along a stalled boundary in eastern GA/southern SC which will lift northeast along the coast late Friday through the weekend. By Friday afternoon, chances for showers and thunderstorms increases for southern zones, esp near typical sea-breeze convective initiation in Onslow/Carteret counties. Max temps will remain in the upper 80s to near 90 deep inland, with mid 80s along the coast. Overnight lows will range from the low 70s inland to mid 70s along the coast/OBX.

Friday Night through Monday, The surface low mentioned above will continue to lift northeast along the Southeastern U.S. Coast through Saturday. The upper pattern becomes more favorable for widespread showers and thunderstorms by early Saturday with deep moist flow from the GOM and western Atlantic Ocean, deepening upper trough over the Midwestern States, with strong shortwaves rotating around the base of the trough. Details related to the surface low's strength and location are difficult to nail down at this time, but it appears that it will lift northeast through the area by late Saturday. Best chances for severe storms will be each afternoon coincident with peak heating. Saturday afternoon's timing will be linked with to surface low providing lift while Sunday afternoon's severe potential will be dependent upon the proximity of the upper trough, and it becoming negatively tilted, with multiple vort maxes rotating aroung the trough helping provide support aloft. Also, given duration of moist southerly flow during this period due to upper trough planted to the NW of the area, cannot rule out flooding potential despite recent dry conditions. Will highlight severe/flood potential in HWO at this time.

Temperatures Saturday through Monday will range from highs near 90 inland, with mid 80s for the coast. Minimum temps will range from the low to mid 70s.

Aviation

12z Tuesday through Saturday Through tonight As of 7 AM Tue, Mainly VFR expected through the TAF period. Approaching shortwave will produce sct to numerous rain showers, esp later this afternoon and tonight. Will continue mention of vcts in terminals for the afternoon hours, though coverage is not at its highest until later this evening. Variable and gusty winds expected in and around thunderstorms, and tempo reduction in vsbys and/or cigs.

Wednesday through Saturday As of 4 AM Tuesday, Sub-VFR conditions possible Wednesday, mainly for OAJ/EWN due to scattered showers and thunderstorms associated with a cold front passage. Vfr conditions return Thursday into Friday, with Sub-VFR possible late Friday night through Saturday associated with a weak surface low moving through the area which will aid in shower/thunderstorms development.

Marine

Through tonight As of 345 AM Tue, Current winds are WSW 10-15 kt across the coastal waters and sounds. The gradient tightens today ahead of an approaching cold front, with SSW/SW winds increasing to 15-25 kt and seas building to 4-7 ft. Sca continues for the waters south of Oregon Inlet, as well as Pamlico sound, this afternoon through overnight for increasing winds and building seas. Could see a few gusts to 25 kt across the northern waters this afternoon though not widespread enough to include in SCA.

Wednesday through Saturday As of 410 AM Tuesday, A cold front will move through the waters early Wednesday, with winds gradually veering behind it. W to NW winds 5-15 kts early Wednesday, becoming NE 5-10 kts in the afternoon. Front will move south of the waters late Wednesday night and Thursday with NE winds continuing at 5-15 kts during the period. Winds will veer E then SE 5-15 kts Friday. Seas will range 2-4 ft Wednesday through Friday. A surface low will lift northeast along the Southeastern U.S. Coast late Friday through Saturday, though details remain with exact location and strength of the low. With southerly winds 15-25 kt expected on Saturday, significantly undercut wave guidance, which was as high as 11-12 ft off the GFS-based Wavewatch, and will forecast SCA seas at 4 to 6 ft on Saturday.

Watches, Warnings, Advisories

Nc, none. Marine, small craft advisory from 2 pm this afternoon to 8 am EDT Wednesday for amz152-154-156-158. Small craft advisory from 2 pm this afternoon to 2 am EDT Wednesday for amz135.

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