textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Gale Watch issued for most of our marine zones for Sunday into Sunday night.

No significant changes to the forecast or messaging regarding Isaias's remnants impacting the area on Sunday.

Aviation section updated for the 18Z TAFs.

KEY MESSAGES

1. Tranquil, dry weather will prevail through Saturday with no significant weather hazards anticipated.

2. The remnants of Hurricane Isaias will impact the area Sunday into Sunday night, bringing moderate rain, breezy conditions, and a low threat of a tornado.

3. Minor tidal flooding possible with Sunday morning's high tide, mainly for coastal areas within Delaware Bay.

DISCUSSION

KEY MESSAGE 1...Tranquil, dry weather will prevail through Saturday with no significant weather hazards anticipated.

High pressure will remain over the area through tonight. This will lead to continued tranquil weather conditions, though it will be a bit breezy until this evening. Cirrus associated with the outflow from Isaias will continue to spread across southern portions of the region, slowly lifting northward. Tonight, winds should quickly diminish, allowing for temperatures to cool fairly quickly in areas where cloud cover has not yet moved in. Overnight lows will likely be in the low 40s across the Poconos, Lehigh Valley, and adjacent areas of far northern NJ, the mid to upper 40s across much of southeastern PA and most of NJ, and low 50s across Delmarva.

On Saturday, the high is expected to begin shifting slowly eastward away from the area. It will remain dry, but cloud cover should steadily increase through the day. As a result, afternoon highs will be a couple of degrees cooler on Saturday than today, but still in the low 70s for most. However, as the high pressure center shifts northeastward, winds will settle out of the east-northeast. The onshore flow will knock temperatures down even further for locations near the coast.

KEY MESSAGE 2...The remnants of Hurricane Isaias will impact the area Sunday into Sunday night, bringing moderate rain, breezy conditions, and a low threat of a tornado.

The primary forecast concern is for Sunday into Sunday night, when the remnants of Hurricane Isaias in the Gulf will be impacting our region. Isaias is expected to make landfall this evening in the western Florida panhandle as it begins interacting with an upper trough. From there, it is expected to undergo extratropical transition and continue northward into the Tennessee Valley through Saturday night, and then northeastward in the direction of our area on Sunday.

Guidance has come into good consensus that Isaias's remnants will impact our region beginning Sunday and into Sunday night, and perhaps lingering into early Monday. Widespread moderate to locally heavy rainfall will be the primary sensible impact, along with breeze ESE winds during the daytime and into the evening hours on Sunday. PWats are modeled to be in the 1.5-2+ inch range, so while the rain should be mainly stratiform in nature, some periods of convectively enhanced heavy rainfall will be possible, especially later in the day and into the evening. Rain will push out of the area overnight, but some showers and drizzle will likely linger overnight and into Monday.

The rainfall forecast has remained mostly unchanged from before, and we expect a widespread 1-2" rainfall event across our area, with potentially for isolated amounts up to 3" possible. Guidance suggests the heaviest rain should occur toward the coast of New Jersey and Delmarva, but this could shift locations. WPC has maintained most of the region in a Marginal Risk (1 of 4) Excessive Rainfall Outlook for Sunday, meaning at least isolated instances of flooding will be possible. Flooding is not anticipated to be a significant concern with this event, however some localized minor urban and poor drainage flooding is possible along with ponding on roads. There are currently no river gauges forecast to reach flood stage, however if the axis of heavier rain shifts north into northern NJ (especially in the 2-3" range), this could cause some gauges in the Raritan basin (namely the Millstone River) to rise to near minor flood stage.

ESE winds will increase to 10-20 mph on Sunday, with gusts up to 30 mph possible (perhaps up to 40 mph along the immediate coast). Temperatures will remain steady in the upper 50s and 60s much of the day. Long story short, a wet and breezy Sunday.

Aside from the rain, with the system lifting over our region, shear and CAPE may reach values just high enough to support some isolated severe storms Sunday evening into Sunday night. Our southern zones remain in a Marginal Risk (1 of 5) Severe Thunderstorm Outlook for Sunday, mainly for the low risk of a brief, weak tornado or damaging wind gust. Some rumbles of thunder will be possible by Sunday evening with the rain.

KEY MESSAGE 3...Minor tidal flooding possible with Sunday morning's high tide, mainly for coastal areas within Delaware Bay.

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, but further north, Reedy Point could hit that level as well. Will wait another forecast cycle or two to determine if any Coastal Flood Advisories are needed. There is higher confidence in Cape May and Cumberland County in NJ and Sussex County in Delaware only reaching spotty minor. Overall though, this event will be nothing like late September.

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

AVIATION /00Z SATURDAY THROUGH WEDNESDAY/

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

Tonight...VFR with increasing high clouds. West-northwest winds in the evening around 5 kt will becoming lgt/vrb overnight. Calm periods likely. High confidence.

Saturday...VFR with SCT/BKN high clouds. Light winds in the morning will eventually settle out of the east at 5-10 kt. High confidence.

Outlook...

Saturday night...VFR. No significant weather.

Sunday through Monday...Restrictions are expected in rain and low clouds. Gusty ESE winds on Sunday.

Monday night through Tuesday...Primarily VFR. Isolated showers and thunderstorms are possible Tuesday afternoon, which could lead to brief restrictions.

Wednesday...VFR. Gusty NNW winds possible.

MARINE

West- northwest winds around 10 kt into this evening, becoming northerly overnight at 5-10 kt. Winds will increase out of the east on Saturday to 10-15 kt with gusts up to 20 kt. Seas 1-3 feet. Fair weather.

Outlook...

Saturday night...No marine hazards currently anticipated with winds under 25 kts and seas below 5 feet.

Sunday through Monday...Gale force ESE wind gusts possible on Sunday, then advisory conditions expected to persist through Monday. Gale Watch issued for most of our marine zones for Sunday into Sunday evening. Seas building to 8-12 feet across the Atlantic waters Sunday into Sunday night before diminishing into Monday. Visibility restrictions are likely in rain and perhaps spray.

Tuesday...No marine hazards expected.

Tuesday night through Wednesday...Advisory conditions probable as a cold front moves offshore. Northwest winds gusting up to 25 kts and seas up to 5 feet.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Gale Watch from Sunday morning through Sunday evening for ANZ430-431-451>455. Gale Watch from Sunday morning through Sunday evening for ANZ481>483-485.