textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

1. 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.

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

DISCUSSION

KEY MESSAGE 1...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 made landfall yesterday evening in the western Florida panhandle and now continues to interact with an upper trough. Extratropical transition is ongoing and the resultant hybrid low will 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 continues to shift where the heaviest corridor of rainfall will be, but continues to most likely be somewhere along the I-95 corridor and southeast, though confidence on narrowing down the exact location remains very low. 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 2...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 /12Z SATURDAY THROUGH WEDNESDAY/

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

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

Tonight...VFR. No significant weather. High confidence.

Outlook...

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

Winds will increase out of the east today to 10-15 kt with gusts up to 20 kt by this evening. Wind gusts of 25 kts possible towards late tonight and early Sunday morning. Seas 1-3 feet, increasing to 2-4 feet tonight. Fair weather.

Outlook...

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. Small Craft Advisory from noon Sunday to 6 AM EDT Monday for ANZ450. Gale Watch from Sunday morning through Sunday evening for ANZ481>483-485.