textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated aviation section for 12Z TAFs.

KEY MESSAGES

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

2. The remnants of what is now Hurricane Isaias will approach the area late this weekend bringing rain and a few thunderstorms back to the region Sunday and Sunday night.

DISCUSSION

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

High pressure will build in today in the wake of a weak cold front, bringing more dry weather. Highs today will generally be in the low to mid 70s so not too far off from average for this time of year. Some cirrus has already started to move into southern areas and this will likely be creeping northward as the day progresses, but sunshine should get through it for the most part.

This evening, the center of high pressure will be centered right over the area but will then start to gradually retreat east and northeastward towards New England heading into Saturday. Expect increasing mid and high level cloudiness through the day Saturday as moisture starts to stream northward in the upper levels. However it remains dry through the day. Most areas will see highs similar to Friday however the winds will be coming around to easterly on the south side of the high to our north so this will keep it a bit cooler near the coast.

KEY MESSAGE 2...The remnants of what is now Hurricane Isaias will approach the area late this weekend bringing rain and a few thunderstorms back to the region Sunday and Sunday night.

The primary forecast concern for the latter part of this weekend into early next week will be the remnants of what is currently Hurricane Isaias in the Gulf. It may intensify further before making landfall somewhere along the northern Gulf coast tonight as it begins interacting with an upper trough. From there, it is expected to undergo extratropical transition and continue northward towards portions of the Ohio Valley through Saturday night, and then northeastward in the direction of our area on Sunday.

Some modest timing discrepancies remain amongst model guidance this morning, but there is strong agreement that the remnants of Isaias will bring some impacts to the region beginning Sunday and perhaps lingering into early Monday. At this point in time, it appears that widespread rain will be the primary impact. It should be noted that PWATs are modeled to be in the 1.5-2+ inch range, so some periods of heavy rainfall will be possible. Our current forecast is for storm totals in the 1.0 to 2.0 inch range. Some areas could see over 2.0 inches, with the best chance of higher totals presently located in the Delmarva and southern New Jersey. WPC has placed 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. We will continue to monitor trends over the coming days.

Aside from the rain potential, with the system lifting over our region, shear and CAPE may reach values just high enough to support some isolated severe storms Sunday/Sunday night, so our southern zones have been placed in a Marginal Risk (1 of 5) Severe Thunderstorm Outlook for Sunday.

Finally, the easterly and southeasterly surface flow preceeding and during the passage of the system may result in minor tidal flooding Sunday into Monday.

AVIATION /10Z FRIDAY THROUGH TUESDAY/

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

Today...VFR. W-NW winds 5 to 10 kt in the morning, then 10 to 15 kt with gusts up to 20 kt in the afternoon. High confidence.

Tonight...VFR. NW winds 5 kt or less, becoming light/variable late. High confidence.

Outlook...

Saturday through Saturday night...VFR. No significant weather.

Sunday through Monday...Sub-VFR conditions are likely in rain and low clouds.

Monday night through Tuesday...Primarily VFR. Isolated showers are possible Tuesday afternoon, which could lead to brief periods of sub-VFR conditions.

MARINE

Winds continue mainly out of the west for today at around 5-10 knots. Seas around 1-2 feet today and tonight.

Outlook...

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

Sunday through Monday...Advisory conditions are possible with wind gusts in excess of 25 kts and seas in excess of 5 feet as the remnants of Hurricane Isaias move through. Visibility restrictions are possible in rain and perhaps spray.

Tuesday...Conditions return to below Small Craft Advisory levels with west to southwest winds around 10-15 knots and seas 2-4 feet.

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...None.