Swell Matrix

Area Forecast Discussion

National Weather Service Newport/Morehead City Nc

828 pm EDT Wed Oct 21 2020

Synopsis

High pressure over the Atlantic will extend into the area through Friday. A weak front will cross Saturday night and dissipate Sunday.

Near Term

Until 6 am Thursday morning As of 815 PM Wed, Forecast in good shape and minimal changes needed for the evening update. Isolated showers across land areas have dissipated with loss of heating but still seeing a few offshore to near Ocracoke. Lamp guidance continues to back off with extent of fog development, but the pattern has changed little over the past 24 hrs and will continue to forecast late tonight into early Thu morning.

Previous discussion, Little change in the pattern this afternoon with an upper level high sitting just off the Mid- Atlantic coast ridging into the southeast CONUS, with broad largely zonal flow over the northern half of the U.S. This regime will largely continue through the short term, although the upper high is expected to weaken through tomorrow as TC Epsilon approaches Bermuda and a weak shortwave begins to trek across the Four Corners region into the Southern Plains.

Consequently, because of little change in the upper pattern the surface reflection has also held strong. North Atlantic high pressure continues to ridge well into the southern U.S. This morning's coastal trough has become more diffuse, although shower activity continues in its vicinity well over the waters. A few clusters of very weak showers developing along areas of weak surface convergence have managed to persist despite the upper level ridge thanks to a continued moist layer below 800 mb.

Tonight's forecast largely follows persistence given the steady pattern. Any existing precip activity will come to an end over land and pick up well offshore, with a few passing showers possible along coastal locales. Main concern tonight will again be the reformation of low stratus and potentially fog, although gradually increasing high cirrus associated with a disturbance over Florida could spoil more widespread fog formation. Best chance for low visibilities should be farther inland. Lows tonight will be slightly cooler as a very weak boundary drops in from the north, falling to around 60 inland but mid to upper 60s OBX.

Short Term

6 am Thursday morning through 6 pm Thursday As of 405 PM Wed, The upper ridge slowly begins to erode tomorrow but the surface high will remain firmly in control. Both global and hi- res guidance point to mainly dry conditions, with early morning low clouds giving way to cumulus by the afternoon and high clouds continuing to stream overhead. Low- level thicknesses fall ever so slightly tomorrow with weak CAA, pointing to highs in the upper 70s to around 80 inland.

Long Term

Thursday night through Wednesday As of 3 AM Wed, Offshore high pressure will cont to extend across the region through the work week with mainly dry conditions and mild temps. A weak front is expected to slowly cross Saturday night then dissipate.

Thu through Sat, Upr rdg centered along the coast Thu night will slowly slide offshore Fri and Sat with cont mainly dry weather. Temps will be a little above normal with highs mainly upr 70s to lows 80s and lows in the 60s with some beach locations around 70.

Saturday night thru Tue, A very weak cold front approaches from the NW Sat then moves into or thru the region Sat night before dissipating. Another high will briefly build in from the N Sunday then slide offshore early next week. Mdls cont to show limited QPF with weak front and cont slight chc to low chc pops Sun. Mon and Tue look mainly dry with stronger front remaining well to the W as high pres slides offshore to the N. Not much change in air mass this period with highs upper 70s/lower 80s and lows mostly 60s.

Aviation

00z Thursday through Monday Through Wednesday As of 8 PM Wed, VFR conditions prevail at the terminals this evening. The main challenge continues to be with the fog/stratus development late tonight. Lamp guidance has backed off bringing in a brief period of sub-VFR conditions at the terminals only around sunrise. However, the airmass has changed little over the past 24 hrs with light/calm winds overnight and near saturated conditions at the surface, so will stick closer to a persistence forecast. Fog should burn off by 13-14z with pred VFR expected Thursday.

Thu through Sunday As of 3 AM Wed, Persistent pattern with offshore high pres extending into the region keeping bulk of time precip free. A weak front will cross Sat night and dissipate Sun with wdly sct to sct shra poss. Will cont to see threat of late night and morn sub VFR in fog/low clouds with bulk of aftn and evenings VFR.

Marine

Through Thursday As of 410 PM Wed, Observation data shows mainly E to NE winds at around 5-10 kt over the waters this afternoon with seas of 3-5 feet over the coastal waters, with the odd 6 footer or two at or beyond 20 nm. Although E to NE winds at 10-15 kt are expected to continue through the short term period, boating conditions will deteriorate as swell from TC Epsilon begins to impact the region starting late tonight. More widespread 6 foot seas encroach on the waters after midnight, increasing to 7-9 feet especially for outer central waters. Dominant wave periods are expected increase to 14-16 seconds. Made some minor trends to SCA expiration times per latest guidance trends but overall advisory suite holds.

Thu night through Sunday As of 3 AM Wed, High pressure will cont to extend SW into the region thru Fri with persistent E to NE winds mainly in the 10 to 15 kt range. A weak front will approach Sat with winds becoming light and becoming more SE twrd evening. As the weak front crosses and dissipates will see winds becoming more NE to E Sun and remain light. Main focus/concern this period will be swells from Tropical Cyclone Epsilon that will grad deepen well offshore. Seas will build to 6 to 8 feet Thu and peak 6 to 9 ft Thu night and early Fri. The swell will very slowly subside over the weekend with seas finally dropping below 6 ft coastal waters later Sunday.

Watches, Warnings, Advisories

Nc, beach hazards statement from 8 am EDT Thursday through Thursday evening for ncz195-196-199-203>205. Marine, small craft advisory from 2 am Thursday to 6 pm EDT Sunday for amz152-154. Small craft advisory from 2 am Thursday to 5 pm EDT Sunday for amz156-158. Small craft advisory from 5 am Thursday to 2 pm EDT Sunday for amz150.

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