textproduct: Wakefield

WHAT HAS CHANGED

Hurricane Isaias has been upgraded to a major, category 3 hurricane. The aviation discussion has also been updated.

KEY MESSAGES

1) Seasonable to slightly above average temperatures and dry conditions through Saturday.

2) Rain chances return Saturday night through early Monday.

DISCUSSION

As of 255 AM EDT Friday...

KEY MESSAGE 1...Seasonable to slightly above average temperatures and dry conditions through Saturday.

Moisture at the upper levels is streaming north and east from Hurricane Isaias early this morning, leading to a high level cloud deck spreading across the local region. Sfc high pressure is in place over the Mid Atlantic and Great Lakes region today with a cold front situated to the south. Today will be on the warm side despite the clouds with highs in the mid to upper 70s. Cooler tomorrow as winds become onshore and breezy. Highs will be in the low 70s. Lows tonight will be in 50s to around 60 for most and in the mid 60s close to the Albemarle Sound. Will note that statistical models indicate temps as low as the upper 40s in the piedmont. Mostly dry through tomorrow evening, but a few showers could sneak into south- central VA as early as late Saturday afternoon.

KEY MESSAGE 2...Rain chances return Saturday night through early Monday.

The forecast for the latter half of the weekend has held fairly steady since yesterday. There is increasing confidence that moisture gets pulled northward and then pushed eastward across the region as Isaias makes landfall and merges with an upper trough in vicinity of the Mid-South. Confidence in timing has increased some as the model guidance has came into better agreement for the onset of accumulated rainfall, showing the 06-12z Sunday timeframe. The 00z ensembles continue to show PW values aob 200% of normal along with a plume of minor instability (<500 J/kg) surging N ahead of the trough. This could lead to heavy rainfall for areas and the slight chance for thunderstorms on Sunday. The highest rainfall totals will likely be in the southern half of the area as there is a hint in the guidance of more enhanced rainfall along a coastal trough. The presence of a coastal trough would also suggest a band of drier air setting up somewhere over the area. This could lead to a large spread in rainfall totals across the area. There is still spread between the 10th and 90th percentile QPF in the 00z/09 ensemble guidance, but amounts generally trended up again. Several ensembles now show a 10th percentile (reasonable low end) QPF of over an inch across the south and ~0.75" elsewhere and a 90th percentile (reasonable high end) of a widespread 2-4" with localized areas upwards of 5". Leaned heavily on the WPC QPF, which is close to the mean amounts from the models. This yielded 2-3" in the southeast, around 2" in Louisa/Fluvanna, and around 1.5" in between where that possible dry slot could set up.

The coastal trough would also suggest an in situ wedge resulting in cooler temperatures and more stable conditions Sunday across the Piedmont. Deeper moisture erodes Sunday night into Monday. However, there are lingering PoPs as the upper trough swings across the region. Behind this system, drier air will filter back in later Monday through the middle of the week. Temperatures should remain near average late this weekend through the middle of next week.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

As of 140 PM EDT Friday...

VFR conditions continue through the 18z taf period. Mainly high clouds with occasional mid-level clouds will linger over the area through the weekend ahead of Hurricane Isaias. CIGs gradually lower Sat from south to north. However, MVFR CIGs likely remain away from the local terminals through 00z Sun. Similarly, dry conditions continue through the 18z taf period. Winds remain light and variable through early Sat. E/ENE winds increase to 5-10 kt inland and 10-15 kt with gusts up to 20 kt along the coast by Sat afternoon.

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 300 AM EDT Friday...

Key Messages:

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

- A short period of Gale conditions is possible with Small Craft Advisories likely Saturday night into early next week as the remnants of Isaias track through the TN Valley and towards the local area, with strong high pressure well off the east coast.

High pressure is noted over the region on surface analysis early this morning. Winds are very light (~5 kt) with waves 1 ft in the bay and seas 1-3 ft offshore. A weak cold front will drop south across the waters, mainly before sunrise, with N winds becoming NE 10-15 kt before falling back into the 5-10 kt range by early afternoon. Seas are expected to stay in 2-3 ft range through most of Saturday. Waves in the bay will be 1-2 ft.

Hurricane Isaias continues to slowly strengthen in the central Gulf early this morning. Current movement is NE but the circulation is expected to turn N this afternoon ahead of a Gulf Coast landfall this evening. While direct impacts are not anticipated locally, the interaction of the remnants of Isaias with an upper-level system is likely to lead to increased E-SE flow from late Saturday afternoon through early Monday morning. The 00z guidance suite has come in a little stronger for winds locally with a brief period of Gale conditions looking more likely Sunday morning into the afternoon. ENE flow begins to strengthen by Saturday afternoon with SCA headlines likely for the southern Ches Bay and lower James River. SCA conditions will expand to all local waters by Saturday evening, continuing overnight. Local wind probs for 34 kt gusts have increased to 50-60% for the southern Chesapeake Bay and Atlantic coastal waters. Will hold off on any Gale Watches with this forecast cycle given that it appears Gale force gusts will only last 3-6 hours at any one location. The strongest winds are forecast across the southern waters near sunrise on Sunday, lifting quickly northward into early Sunday afternoon. Winds will rapidly shift from E-SE as the low makes its closest approach. The gradient is forecast to slacken considerably by Sunday evening. Waves in the bay build to 3-5 ft Sunday (highest S) before relaxing to 2-3 ft early Monday AM. Seas offshore increase to 6-8 ft nearshore and 7-10 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 late Monday into Tuesday with a stronger front expected Tuesday into Wednesday. Decent cold advection behind this second front could lead to another period of SCA conditions midweek.

AKQ WATCHES/WARNINGS/ADVISORIES

MD...None. NC...None. VA...None. MARINE...Small Craft Advisory from 7 PM Saturday to 7 PM EDT Sunday for ANZ630-631. Small Craft Advisory from 4 PM Saturday to 7 PM EDT Sunday for ANZ632. Small Craft Advisory from 4 PM Saturday to 4 PM EDT Sunday for ANZ633-639. Small Craft Advisory from 4 PM Saturday to 4 AM EDT Sunday for ANZ634. Gale Watch from late Saturday night through Sunday afternoon for ANZ634. Small Craft Advisory from 10 PM Saturday to 4 PM EDT Sunday for ANZ635>637. Gale Watch from Sunday morning through Sunday evening for ANZ650-652-680-682. Small Craft Advisory from 10 PM Saturday to 4 AM EDT Sunday for ANZ654-656. Gale Watch from late Saturday night through Sunday afternoon for ANZ654-656-684-686. Small Craft Advisory from 4 PM Saturday to midnight EDT Saturday night for ANZ658. Gale Watch from late Saturday night through Sunday morning for ANZ658-688.