Marine Weather and Tide Forecast for Carrollton, VA

KEY MESSAGES
1) Rain chances increase tonight into Sunday as the remnants of Hurricane Isaias move farther inland. There is a Slight Risk (level 2/5) for severe weather Sunday.

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

3) Nuisance to Minor tidal flooding is expected with the high tide cycle Sunday for portions of Hampton Roads, the western shore of the Chesapeake Bay and the lower Maryland eastern shore.

DISCUSSION
As of 310 AM EDT Saturday...

KEY MESSAGE 1...Rain chances increase Saturday night into Sunday as the remnants of Hurricane Isaias move farther inland. There is a Slight Risk (level 2/5) for severe weather Sunday.

Hurricane Isaias made landfall on the FL panhandle late last evening and was just starting to cross into Alabama as of 2am as it degrades. Here locally in the Mid-Atlantic sfc high pressure is still in charge for now. Isaias will transition into an extra- tropical system as it treks north today toward TN/KY/WV. A warm front will extend east from the parent low and push north towards the FA. A subtle coastal trough forming along the front along with high pressure ridging down the mountains will set up a relatively weak CAD over the piedmont tonight into tomorrow. The FA will spend Sunday morning-mid day in the warm sector, then the low will progress northeast and drag a cold front through Sunday evening. The evolution of this system will bring widespread rain to the area as well as the chance for a few tornadoes and strong winds.

Rain will arrive ahead of the warm front as early as this afternoon to far southern/southwestern counties then spreads across the area in earnest after 8pm, continuing overnight. This is when the bulk of appreciable rainfall should fall and when the aforementioned coastal trough could locally enhance rainfall near the Outer Banks.
The 00z high res models and ensembles as well as the global deterministic models are leaning hard on the idea of a dry slot across central portions of the area, roughly along the I-95 corridor, after the warm front lifts through the area. A secondary line of showers/storms would then impact the area ahead of the cold front. As a result, the projected precip totals are less than previous model suites. The high res models indicate a widespread ~0.5" with locally higher 1-2" along coastal SE VA and NE NC.
Meanwhile, a global ensemble like the GEFS has something similar in its 10th percentile with a mean of 1-2" for most and 2-2.5" for the southeast. The 90th percentile has around 3". The NBM, of course, reflects this spread with a wide range in its percentiles from less than an inch in the 10th to around 3" in the 90th. The dry slot was incorporated into the QPF since confidence is increasing in this solution. Now expecting 1-1.5" total along the coast and across the piedmont with central portions of the area receiving less than an inch. Areas near the Albemarle Sound may experience locally higher amounts of 2-3". Flood threat is low, but urban and poor drainage areas could see localized flooding Sunday morning.

The threat for severe weather comes in as the low traverses northern VA/MD and drags a cold front through the local area. Most of the CAMs depict a broken line of convection and/or supercells Sunday afternoon ahead of the front. An influx of instability to around 800- 1000 J/kg (per RRFS/REFS) would support strong to severe storms. The modeled wind profile is favorable for supercells with SE winds at the sfc, strengthening deep layer shear, and curved hodographs. This could mean strong to severe winds and even a few tornadoes. Of course if the dry slot is never realized, it would likely put a damper on instability and therefore severe chances. Also, the CAD setup will likely limit severe potential for at least areas NW of Richmond. SPC has upgraded the entire FA to a Slight Risk with a 5% tornado risk and 15% severe wind risk.

Regarding temperatures, highs will be in the upper 60s in the piedmont and low 70s E of I-95 today. Tomorrow, highs will range from the upper 70s/around 80 in the southeast to the low 70s in the northwest. Breezy conditions are forecast as well with gusts of 20- 25mph inland and 25-35mph at the coast starting this afternoon through tomorrow, peaking early Sunday morning.

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. This will result in a brief warm-up with highs in the mid to upper 70s on Monday and low 80s on Tues. Per usual, the Eastern Shore can expect to be several degrees cooler each day. Still a tad warm on Wed, then cooling back to seasonal norms later in the week through the weekend. Mostly dry through mid-week, then trending toward a more unsettled pattern starting Thurs.

KEY MESSAGE 3..Nuisance to Minor tidal flooding is expected with the high tide cycle Sunday for portions of Hampton Roads, the western shore of the Chesapeake Bay and the lower Maryland eastern shore.

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, potentially approaching moderate flood locally would be the northern Neck along the tidal Potomac. 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 /12Z SATURDAY THROUGH WEDNESDAY/
As of 655 AM EDT Saturday...

VFR conditions prevail for the first half of the 12z/10 TAF period. High level cloud cover will continue across the area today well out ahead of Hurricane Isaias which made landfall on the FL panhandle late last evening. Easterly winds increase to around 10 kt today, becoming gusty at ORF and ECG during the afternoon through the rest of the period. Clouds thicken and lower later in the period, becoming MVFR everywhere but SBY after 00z tonight. CIGs drop further to IFR at RIC and ECG after 06z. Light rain has already made its way into far southern portions of the forecast area and is already showing up in the obs at ECG. Rain will spread to the rest of the terminals during the evening and will continue through tomorrow.

Outlook: Widespread rain moves into the area from south to north Sat night into Sun associated with the remnants of Isaias. Degraded VIS and CIGs are likely. Additionally, breezy conditions are expected late Sat night into early Sun with E winds increasing to 10-15 kt with gusts up to 20 kt inland and 15-20 kt with gusts up to 25-30 kt along the coast. Winds become SE Sun afternoon behind a warm front lifting north.

MARINE
As of 310 AM 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.

Isaias is rapidly transitioning into an extratropical cyclone as it interacts with a strong shortwave aloft over the central Gulf Coast.
1026mb high pressure remains over the Mid-Atlantic ahead of Isaias' remnant circulation, leading to easterly winds 5-10 kt over the local waters. Waves are around 1 foot in the bay with seas around 2 ft.

The surface high will transition slowly eastward today and strengthen to 1030+mb as the extratropical remnants of Isaias slowly weaken over the Tennessee Valley. The resulting pressure gradient will steepen across the region with easterly winds increasing to 15-20 kt with gusts to 25 kt from south to north through the afternoon. No changes were required to the previously issued SCA headlines with small craft conditions likely in the Currituck Sound, lower James River, and Chesapeake Bay by mid to late afternoon. Winds increase further overnight with SCAs going into effect for the remaining zones. Have added a ramp up SCA for the Atlantic zones north of Parramore Island tonight. Also upgraded the previous Gale Watches to Gale Warnings for the mouth of the bay and ocean zones south of Parramore Island as we are within 24 hours of the strongest winds. A warm front lifts northward tonight/Sunday with easterly winds becoming SE and increasing to 20-25 kt with gusts to 30 kt in the bay/sound/rivers and 25-30 kt with gusts to 35 kt for the mouth of the bay and Atlantic coastal waters. This period of gale conditions will be rather brief (~6-9 hours at any one point) with winds expected to diminish slightly and become SSE behind the warm frontal passage. Ongoing Gale Watches north of Parramore Island will likely be upgraded to Gale Warnings on the day shift today.

The gradient is forecast to slacken considerably by Sunday evening.
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 Sunday night/Monday AM.
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. There is a chance that a High Surf Advisory may be needed Sunday, especially for the eastern shore, but confidence is not high so will hold off for now.

A cold front is forecast to cross the waters in the wake of the departing system Monday morning. Latest guidance suggests another brief period of SCA conditions are possible across portions of the Ches Bay through early afternoon as cooler and drier air filter into the region. Another front crosses the waters Wednesday with SCA conditions possible once again.

AKQ WATCHES/WARNINGS/ADVISORIES
MD...None.
NC...None.
VA...None.
MARINE...Small Craft Advisory from 7 PM this evening to 7 PM EDT Sunday for ANZ630-631.
Small Craft Advisory from 4 PM this afternoon to 7 PM EDT Sunday for ANZ632.
Small Craft Advisory from 4 PM this afternoon to 4 PM EDT Sunday for ANZ633-639.
Small Craft Advisory from 4 PM this afternoon to 4 AM EDT Sunday for ANZ634.
Gale Warning from 4 AM to 1 PM EDT Sunday for ANZ634.
Small Craft Advisory from 10 PM this evening to 4 PM EDT Sunday for ANZ635>637.
Small Craft Advisory from 1 AM to 10 AM EDT Sunday for ANZ650- 652.
Gale Watch from Sunday morning through Sunday evening for ANZ650-652-680-682.
Small Craft Advisory from 10 PM this evening to 4 AM EDT Sunday for ANZ654-656.
Gale Warning from 4 AM to 4 PM EDT Sunday for ANZ654-656-684- 686.
Small Craft Advisory from 4 PM this afternoon to midnight EDT tonight for ANZ658.
Gale Warning from midnight tonight to noon EDT Sunday for ANZ658-688.