textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated the Aviation section with the 12Z TAFs.

KEY MESSAGES

1. The remnants of Isaias brings rain, some potentially heavy at times, gusty winds and a low risk for an isolated severe thunderstorm.

2. Minor tidal flooding possible with this morning's high tide, mainly for coastal areas within Delaware Bay. A Coastal Flood Advisory is in effect for Kent County, DE.

DISCUSSION

KEY MESSAGE 1...The remnants of Isaias brings rain, some potentially heavy at times, gusty winds and a low risk for an isolated severe thunderstorm.

A closed mid level low and surface low, the remnants of former Hurricane Isaias, is forecast to slide across the Mid-Atlantic region tonight into early Monday morning. As this occurs, it is forecast to weaken further with the closed mid level low opening up more into a trough. The main impacts for our area will be widespread rainfall and some gusty winds. An east to southeast robust low-level jet (around 925 mb) on the order of 40-60 knots will overspread our area this morning and this will rapidly increase the warm air advection and moisture advection across the region. PWAT values are expected to surge into the 1.75 to 2.25 inch range. As this coincides with strong forcing for ascent today, some periods of heavier rain should occur. Total rainfall amounts still look to be 1-2 inches across the entire area, however up to 3 inches will be possible where some enhancement and/or embedded convective elements occur. This event should initially be in the form of stratiform rain before transitioning to more convective/showery tonight into early Monday morning. WPC has maintained most of the region in a Marginal Risk (level 1 out of 4) for excessive rainfall for today into tonight, which means isolated instances of flash flooding will be possible. There are currently no river gauges forecast to reach minor flood stage, however if even heavier rain occurs into northern NJ (especially 2.5+ inches), this could cause some gauges in the Raritan basin (the Millstone River) to rise to minor flood stage. If rainfall rates become high enough for a time, then some urban/roadway flooding will also be possible.

As the low-level jet moves across the area and the warm sector gradually spreads northward later today, an easterly wind will increase and become gusty. Wind gusts up to 30 mph are anticipated inland with gusts up to 40 mph along the coast. The winds should diminish tonight as the remnant surface low slides across our area and the low-level jet shifts away from our region.

While this is the remnants of a tropical system, it has had plenty of time being a post-tropical system prior to reach our area. Nevertheless, low-level shear profiles increase quite a bit for a time this afternoon into evening as the main rain shield starts to shift north and east of our area. During this time, some instability may try to advect northward across Delmarva into southern New Jersey especially, but the window of opportunity is rather small where lingering stronger deep-layer shear overlaps with some increase in instability. Perhaps a few transient low- topped supercells with an isolated damaging wind gust are possible as a result, but confidence remains low. The severe scenario, however, is highly contingent on how much higher dew points advect northward with enough low-level instability, and this looks to be greater to our south and southwest. The risk for a weak/brief tornado in our area remains very low.

Some showers linger early Monday morning, especially from about the I-95 corridor on south and east, then drying should quickly occur during Monday as a north to northwest wind increases for a time and the entire weakening system exits to our east and northeast.

KEY MESSAGE 2...Minor tidal flooding possible with this morning's high tide, mainly for coastal areas within Delaware Bay. A Coastal Flood Advisory is in effect for Kent County, DE.

With a period of east/southeasterly flow expected and the upcoming New Moon, increased tidal levels are expected later this weekend. This will result in spotty to widespread minor tidal flooding, mainly for coastal communities along Delaware Bay. The only forecast point currently forecast to reach widespread minor is Bowers Beach. As a result, went ahead an issued a Coastal Flood Advisory from 7 AM to 1 PM for Kent County, DE. An additional round of Coastal Flood Advisories may be needed for some Delware Bay communities for the Monday morning high tide.

This won't be a significant event for the Atlantic Ocean coastline, where only spotty minor tidal flooding is expected from Barnegat Bay on south. This includes the Delaware Beaches and back bay communities in Sussex County, DE.

Overall, this event will be nothing like late September.

The current forecast has no tidal flooding for areas along the Atlantic coastline north of Barnegat Bay. The forecast for the tidal Delaware River and Chesapeake Bay also has tide levels staying below flood stage at this time.

AVIATION /13Z SUNDAY THROUGH THURSDAY/

The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas.

Today...MVFR conditions have developed and will continue to drop to IFR due to lowering ceilings. Widespread rains continue through the day with visibility restrictions. Periods of LIFR conditions possible. Pockets of moderate to heavy rain at times with VCTS late afternoon. Winds also remain out of the east but increase to 10-15 kt with gusts to 20-25 kt. A few gusts up to 30 kts possible at KMIV and KACY. Moderate confidence.

Tonight...Sub-VFR conditions prevail. Rain becomes more scattered overnight with VCTS. Vis restrictions may ease to MVFR, but IFR/LIFR ceilings remain. Winds gradually back to the NNE and ease to around 10 kts. Moderate confidence in low ceilings, but low confidence overall.

Outlook...

Monday...Sub-VFR possible in the morning due to low clouds. Conditions gradually trend towards VFR throughout the day.

Monday night through Tuesday...Primarily VFR. No significant weather.

Wednesday...VFR. Gusty WNW winds possible.

Thursday...VFR. No significant weather.

MARINE

Small Craft Advisories for the coastal ocean waters were extended into Monday night.

For Sunday, easterly winds increase further to 30 kts with occasional gusts upwards of 35 kts, particularly this morning. Seas continue to build to 7-10 feet by Sunday afternoon. A Small Craft Advisory is in effect for the Delaware Bay and all of the Atlantic coastal waters until tonight. Due to the occasional nature of gale force gusts, the Gale Watch has been cancelled for the offshore waters. Visibility restrictions are likely in rain which could be moderate to heavy at times.

Winds shift more southerly and diminish below advisory criteria as the low center moves across the waters overnight before shifting more northerly as the low begins to depart early Monday morning. Seas will be slow to subside, staying elevated around 6-8 feet.

Outlook...

Monday...SCA conditions for the coastal ocean waters due to lingering seas of 6-8 feet and northerly wind gusts upwards of 25 kts that gradually diminish into Monday night.

Tuesday through Thursday...No marine hazards expected.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...Coastal Flood Advisory until 1 PM EDT this afternoon for DEZ002. MD...None. MARINE...Small Craft Advisory until 10 PM EDT this evening for ANZ430- 431. Small Craft Advisory until 4 AM EDT Tuesday for ANZ450. Small Craft Advisory until 4 AM EDT Tuesday for ANZ451-452. Small Craft Advisory until 2 AM EDT Tuesday for ANZ453>455.