textproduct: Wakefield

WHAT HAS CHANGED

The timing of this system has trended faster. Gale Watches have been upgraded to Gale Warnings across all of the coastal waters with Gale Warnings remaining in effect for the mouth of the Chesapeake Bay. Coastal Flood Advisories have been issued for portions of east central VA along the Bay and tidal Rappahannock/Potomac. Coastal Flood Statements have been issued for Hampton Roads, and the tidal York/James.

The severe threat has increased across south-central Virginia Sunday afternoon and evening. Rainfall totals have trended lower for this weekend inland.

KEY MESSAGES

1) Rain chances increase tonight into Sunday as the remnants of Post- Tropical Cyclone Isaias move farther inland. There is a Slight Risk for severe weather Sunday.

2) A brief warmup is expected early next week with cooler temperatures later in the week.

3) Coastal Flood Advisories have been issued for portions of east-central VA along the Bay and tidal Rappahannock/Potomac for minor flooding Sunday. Coastal Flood Statements have been issued for Hampton Roads, the tidal York/James, and the bayside of the lower Maryland and VA eastern shore for nuisance flooding Sunday.

DISCUSSION

As of 305 PM EDT Saturday...

KEY MESSAGE 1...Rain chances increase tonight into Sunday as the remnants of Post-Tropical Cyclone Isaias move farther inland. There is a Slight Risk for severe weather Sunday.

Isaias is now a post-tropical cyclone centered over central AL. Meanwhile, a strong area of high pressure (~1035 mb) was located over interior portions of New England. This has resulted in CAD across the Mid Atlantic with the associated warm front across the Deep South and widespread cloud cover across the region. The remnants of Isaias will continue to track NE into Sun. As this occurs, the system will occlude and form a secondary surface low across the western Carolinas early Sun that will track NE across the local area late Sun afternoon into Sun evening. As this secondary surface low lifts NE, it will help lift a warm front north through the day.

Isentropic ascent has allowed for light showers aloft to continue to overspread the local area this afternoon. However, RH values were low with 50-60% RH common given temps in the low-mid 70s and dew points in the 50s for most (60s across far SE VA/NE NC). As such, most of these showers have been virga with only occasional, brief light sprinkles reaching the surface. However, as the low-levels saturate later this afternoon into tonight, RH will increase and rain will become more widespread from south to north. A widespread, wetting rain is still expected tonight into early Sun. Rain could be heavy at times. However, models continue to show a lull in the precip from late Sun morning into early Sun afternoon. This lull should allow for destabilization to occur, especially if some cloud breaks become present. However, the degree of destabilization remains in question with the HRRR showing more widespread convection (and therefore lower instability) whereas the NAM, RRFS, and several of the WRFs show lower coverage of showers and storms in the afternoon. Given the general model consensus for a lull in the precip, the HREF shows mean CAPE of above 1000 J/kg. The REFS is slightly low (700-1000 J/kg). In either case, this is plenty of instability (if realized) for October to cause severe weather.

CAMs continue to show either a line or broken line of supercells developing across west-central NC early Sun afternoon, moving NE with time into the local area by late Sun afternoon into Sun evening. This convection forms behind a mid-level dry slot which should aid in updraft growth and maintenance. Additionally, since this convection forms along a theta-e boundary on the SE side of a surface low, rich moisture will likely be in place ahead of the convection along with backed (SE) surface winds. This is also colocated with a strengthening LLJ which will add ample shear and helicity for rotating updrafts. As such, the threat for severe weather continues to increase with the main threat being a few tornadoes and/or damaging winds. SPC has a slight (level 2/5) risk for severe storms across the western two-thirds of the FA with a marginal risk along the coast. Given the track of the surface low and more favorable timing, the greatest threat for tornadoes is across portions of south- central VA late Sun afternoon into Sun evening. Storms should gradually weaken east of I-95 given the loss of diurnal instability. However, isolated severe weather could persist to the coast Sun night. The most likely timing for severe weather is from 2-10 PM. Will note that exact timing could change depending on the speed of the system as whole.

This line marks the end of the severe threat. However, another round of showers appears increasingly likely on the backside of the low Sun night into early Mon morning. Rain could be locally heavy even with this round. Given the multiple rounds of convection, confidence in exact rainfall totals has decreased. The current forecast shows 0.5-1" of rain for central VA and interior NE NC with 1-2" along the coast and across the western Piedmont. That being said, locally higher totals of 2-3"+ remain possible. WPC has maintained a marginal risk for excessive rainfall (ERO) tonight along the Albemarle Sound and Sun across far eastern portions of the FA.

Otherwise, E/ENE winds of 5-10 mph inland and 10-15 mph with gusts up to 20-25 mph along the coast this afternoon increase to 10-15 mph with gusts up to 20-25 mph inland and 15-20 mph with gusts up to 30- 35 mph along the coast late tonight into early Sun. The strongest winds look to be along and just north of the warm front as it lifts north across the area. Winds become SSE/SE and remain breezy (especially along the coast) Sun afternoon. Given the retreating CAD Sun, highs may struggle to warm above 70F across the far NW Piedmont but should be able to warm into the upper 70s across south-central and SE VA as well as NE NC. A few locations may even reach 80F.

KEY MESSAGE 2...A brief warmup is expected early next week with cooler temperatures later in the week.

Aloft, a ridge centered across the central CONUS gradually builds into the region through the week. Meanwhile, surface high pressure remains centered across the Deep South through midweek before a second area of high pressure builds in from the north late in the week. As such, a warmup is expected with highs in the 70s for most Mon, lower 80s for most Tue (mid-upper 70s across the Eastern Shore), and mid 80s for most Wed (upper 70s to near 80F for the Eastern Shore). The biggest change to the temperature forecast was that high temps Wed have trended much warmer given that the ridge is expected to be a bit more present across the local area. Temps gradually cool late in the week but remain at or above average through Fri. Otherwise, mainly dry conditions are expected from Mon- Thu.

KEY MESSAGE 3...Coastal Flood Advisories have been issued for portions of east-central VA along the Bay and tidal Rappahannock/Potomac for minor flooding Sunday. Coastal Flood Statements have been issued for Hampton Roads, the tidal York/James, and the bayside of the lower Maryland and VA eastern shore for nuisance flooding Sunday. A high Surf Advisory has been issued for the eastern shore for ~8 ft nearshore waves.

A rapid rise in water levels is expected with the Sunday high tide cycle, occurring mainly in the morning for the lower Chesapeake Bay, lower James, and during the afternoon farther north across the middle Peninsula/northern Neck and late afternoon into early evening for the lower Maryland eastern shore Bay zones. Given the E-SE wind direction, the highest impacts are across areas in the Advisory (east central VA along the tidal Rappahannock/Potomac and west shore of the Bay. This should be just one tide cycle with the fast moving nature of this system and winds becoming S-SW later Sunday and Sunday night.

AVIATION /19Z SATURDAY THROUGH THURSDAY/

As of 155 PM EDT Saturday...

Widespread cloud cover will persist through Sunday evening in association with the remnants of Post-Tropical Cyclone Isaias. CIGs were mainly VFR this afternoon but will gradually lower to MVFR at RIC/ECG by around 00-02z Sun, ORF/PHF by around 1-2z, and SBY around 9-10z. CIGs continue to lower to IFR at RIC/ECG by around 4-6z Sun, ORF/PHF around 6-8z, and SBY around 12z. IFR/LIFR CIGs are then expected to prevail through at least early Sun afternoon. CIGs may improve to MVFR Sun afternoon across most terminals behind a warm front lifting north. Showers spread north across the area late this afternoon into early Sun with the heaviest rain (and lowest VIS) expected late tonight into early Sun morning. A break in the convection is possible from late Sun morning into mid- afternoon on Sun with another round of showers and storms moving east across the area late Sun afternoon into Sun evening. The late day convection has the best chance for lightning and gusty winds as well as the potential for an isolated tornado. However, severe weather chances are highest inland and taper off near the coast. Otherwise, winds were generally E/ENE 5-10 kt inland and 10-15 kt with gusts up to 20-25 kt along the coast this afternoon. Winds increase late tonight into Sun morning, especially along the coast where 15-20 kt sustained winds with gusts up to 25-30 kt are possible. Winds become SE by Sun afternoon behind a warm front, gradually diminishing.

Outlook: Showers taper off Sun night into Mon morning with dry conditions expected after sunrise on Mon. CIGs are also expected to gradually improve Sun night into Mon.

MARINE

As of 400 PM EDT Saturday...

Key Messages:

- Sub-SCA conditions prevail through the first half of today.

- Gale Warnings and Small Craft Advisories in effect starting this afternoon into Sunday as the remnants of Isaias track through the TN Valley and towards the local area, with strong high pressure well off the east coast.

Even with Post-Tropical cyclone Isaias now a relatively weak sfc feature over Alabama, the pressure gradient has increased rather quickly today as a sfc trough now extends NE into the Carolina coastal plain and SE VA, as strong sfc high pressure of ~1031mb is centered just off the coast of New England. Ended up raising SCAs several hrs earlier for the lower Bay, lower James, and southern coastal waters as E winds have been ~20 kt with higher gusts since late this morning. Waves are 3-4 ft in the lower Bay, and seas are 4-5 ft in the ocean S of Cape Charles. Farther north, winds are elevated but somewhat lighter.

The overall trends have been for a faster arrival of the stronger winds and this appears to continue for the overnight hrs and on Sunday. As the sfc trough and associated warm front lift northward overnight, pressure falls should enhance the E-SE winds enough for strong SCAs to low-end Gales, primarily during the 06-12Z timeframe south, and 3-6 hrs later to the north. While it looks marginal, decided to upgrade the remaining Gale Watches to Warnings for the ocean (so now Gales are in effect for all Ocean zones and for the mouth of the Bay). Strong SCAs are in effect elsewhere.

The gradient is forecast to slacken considerably from N to S by Sunday afternoon. Waves in the bay build to 3-5 ft Sunday (but up to 5-7 ft at the mouth of the Bay), before relaxing to 2-3 ft later in the day. Seas offshore increase to 6-9 ft nearshore and 7-11 ft in the 20-60 nm zones. 5+ ft seas and SCA headlines will likely linger well into Monday for the Atlantic coastal waters.

A cold front is forecast to cross the waters in the wake of the departing system Monday morning. Another period of SCA conditions is likely for the Bay through early afternoon as cooler and drier air filters into the region. Mainly sub-SCA conditions Mon night through midweek as the arrival of the mid- week front has slowed down and may not be until Thursday or Friday.

AKQ WATCHES/WARNINGS/ADVISORIES

MD...High Surf Advisory from 6 AM to 6 PM EDT Sunday for MDZ025. NC...None. VA...High Surf Advisory from 6 AM to 6 PM EDT Sunday for VAZ099-100. Coastal Flood Advisory from 11 AM to 6 PM EDT Sunday for VAZ075>077-521-522. Coastal Flood Advisory from 9 AM to 4 PM EDT Sunday for VAZ078- 085-086. MARINE...Small Craft Advisory until 7 PM EDT Sunday for ANZ630>632. Small Craft Advisory until 4 PM EDT Sunday for ANZ633-639. Small Craft Advisory until 4 AM EDT Sunday for ANZ634-656. Gale Warning from 4 AM to noon EDT Sunday for ANZ634-654-656- 684-686. Small Craft Advisory from 7 PM this evening to 4 PM EDT Sunday for ANZ635>637. Small Craft Advisory from 10 PM this evening to 7 AM EDT Sunday for ANZ650-652. Gale Warning from 7 AM to 4 PM EDT Sunday for ANZ650-652-680- 682. Small Craft Advisory from 7 PM this evening to 4 AM EDT Sunday for ANZ654. Small Craft Advisory until midnight EDT tonight for ANZ658. Gale Warning from midnight tonight to 10 AM EDT Sunday for ANZ658-688.