Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
Issued by NWS Mt. Holly, NJ
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861 FXUS61 KPHI 161918 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 318 PM EDT Mon Sep 16 2024 .SYNOPSIS... High pressure will be in control through tonight. One area of low pressure tracks northwestward into the Carolinas while a secondary low passes off to our east, bringing increasing chances for showers across our area through midweek. Unsettled conditions persist through the end of the week as high pressure tries to build in for next weekend and early next week. && .NEAR TERM /THROUGH TUESDAY/... High pressure to the northeast continues to weaken allowing an increased onshore flow with added moisture to continue over the area. Showers haven`t made it too far north as of the late afternoon, but chances do increase tonight from south to north. For tonight slight chance pops will be across Delmarva and south NJ. On Tuesday the pops continue to increase, reaching up into central NJ and the Lehigh Valley of PA. Overall QPF is expected to be less than a tenth of an inch for tonight and Tuesday, with the highest totals across Delmarva. Lows tonight will remain on the mild side with the onshore flow and clouds in place. Readings will fall to the mid/upper 60s for the S/E areas and mid/50s to low 60s elsewhere. On Tuesday, it`ll continue rather cloudy as the onshore flow continues scattered showers are expected, especially for the southern half of the CWA, as moisture associated with a low pressure system approaches. Up across the far north, breaks in the clouds and some limited sunshine is possible. Highs on Tuesday will be similar than todays with mid/upper 70s common. Winds will be Northeast to East around 10 mph. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... The remnants of Potential Tropical Cyclone 8, its associated tropical moisture, and a secondary coastal low will be the main talking points of the short term period. Tropical moisture will be advected north during the term resulting in periods of heavy rain supported by several shortwaves embedded in the upper flow. The first wave still looks to be on pace to affect the region late Tuesday night into the day on Wednesday. This will be associated with a secondary coastal low that develops off the Carolinas separating itself from the upper low associated with PTC8. This secondary low will lift northward paralleling our coastline while remaining offshore. The biggest difference at this point amongst models, is just how far offshore this secondary low will be. If the low, takes a closer track to the coast, then more in the way of heavy rain looks plausible during the day on Wednesday. If the track is further offshore as indicated by some guidance, there may be enough dry air filtering in from the north to keep any beneficial rainfall offshore. Regardless, PWATs are forecast to be around 2 inches, so some tropical related downpours are possible through the period. In terms of the flood risk, the risk really isn`t that high due to the dry conditions that have occurred over the past couple of weeks. This is supported well by the Weather Prediction Center which now keeps only southern NJ and the Delmarva in a Marginal Risk for Excessive Rainfall on Wednesday. Heading into Wednesday night and Thursday, the forecast varies significantly due to the fact that global and short-range guidance are struggling to depict the upper pattern. The GFS keeps an open deep trough over the East Coast, while the ECMWF closes the trough into a closed low which meanders overhead. So, while there is potential for showers to continue into Wednesday night and Thursday, the confidence in this in actually occuring is low. As a result, have kept a 20-40% chance of showers across the entire region during this period. Storm total rainfall through Thursday is expected to be around 0.50-1.00 inches from the I-95 south and east with roughly 0.25-0.50 inches north and west of I-95. In terms of temperatures, we are looking at highs in the 70s on Wednesday and Thursday with lows in the 60s thanks to the tropical airmass in place. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... The blocking pattern aloft will likely continue as a deep trough will remain within the vicinity of the East Coast through much of the period. This will yield unsettled and cool conditions through the end of the week, before turning potentially more tranquil to kick off the weekend into next week. As of now, most of the deterministic guidance keeps the deep upper trough over the East Coast through about Saturday before an upper ridge begins to move over the top into early next week. This will keep the threat for showers and cool weather to occur through Friday, before high pressure builds to our north and east for Saturday onwards. While there will still be a chance of a shower or two over the southern portions of the area, for the most part the forecast is trending drier for the weekend and into early next week. However, with blocking patterns, weather features are often difficult to predict, so there likely will be some variance to the forecast in the coming days. In terms of temperatures, most of the region does appear to stay on the cooler side of normal with temps mostly in the 70s during the day and in the 50s at night. && .AVIATION /19Z MONDAY THROUGH SATURDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...Lowering CIGS across the terminals this evening with most sites expected to go IFR overnight. The CIGS lower first for KACY/KMIV and latest for KRDG/KABE. The timing and exact CIGs are medium confidence at best. A couple stray showers are possible for southern DE. East to Northeast winds around 10 knots decreasing to around 5 kts overnight. Medium/low confid overall. Tuesday...Low CIGS early then improvement to VFR by late morning. A few showers in the afternoon are possible, but not included in the 18Z TAFs. East winds increasing to around 10 knots. Medium confid. Outlook... Tuesday night through Thursday...Sub-VFR conditions likely with periods of rain and isolated thunderstorms. Locally heavy rain is possible at times especially Tuesday night into Wednesday. Thursday night through Saturday...Primarily VFR expected. Slight chance for a shower or thunderstorm which may cause temporary restrictions. && .MARINE... SCA conditions will continue across the waters, save the upper Delaware Bay, tonight and Tuesday. East to Northeast winds around 15 kts with gusts 25 to 30 kts expected. Seas will be generally 5 to 8 ft. Fair this evening then scattered showers possible for the Delaware waters late tonight and all waters for Tuesday. Outlook... Tuesday night through Wednesday night...SCA conditions to continue due to elevated seas around 5-6 feet. As a result, there will likely will need to be an extension to the current SCA in effect. Thursday...SCA conditions possible as seas will be around 4-5 feet. Thursday night through Saturday...SCA conditions likely to redevelop with seas building from 4-6 feet to 6-8 feet. Winds may gust up to 30 kt on Saturday as well. Rip currents... For Monday and Tuesday, east winds will average 15 to 20 mph with breaking waves of 2 to 4 feet with an 8 to 9 second period. This results in a HIGH risk for the development of dangerous and life threatening rip currents for the Delaware Beaches and Jersey Shore. A Rip Current Statement is now in effect for both Monday and Tuesday. For specific beach forecasts, visit weather.gov/beach/phi && .TIDES/COASTAL FLOODING... Continued onshore flow will result in some minor tidal flooding, mainly along the Atlantic coast and within the Delaware Bay. Coastal Flood Advisories were issued for tonight`s high tide for coastal locations in South Jersey and southern Delaware. For the Delaware Bay, a Coastal Flood Advisory was issued for Cumberland County, NJ and Kent, DE. For the upper Delaware Bay, tidal Delaware River, and central and northern NJ coast (north of Atlantic County), only spotty minor flooding is expected for tonight`s high tide. As we get into the middle of the week, water is anticipated to continue to pile up in the back bays and up the Delaware River with prolonged onshore flow. This may result in further advisories as early as Tuesday evening. However, only minor flooding is expected at this time. Will let the current advisories for Monday night run their course before deciding on an extension and/or expansion of the Coastal Flood Advisory. No tidal flooding is expected along the Eastern Shore of Maryland currently. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...Coastal Flood Advisory until midnight EDT tonight for NJZ021>025. High Risk for Rip Currents through Tuesday evening for NJZ014- 024>026. DE...Coastal Flood Advisory until midnight EDT tonight for DEZ002>004. High Risk for Rip Currents through Tuesday evening for DEZ004. MD...None. MARINE...Small Craft Advisory until 6 PM EDT Tuesday for ANZ431. Small Craft Advisory until 6 AM EDT Wednesday for ANZ450>455. && $$ SYNOPSIS...DeSilva/Hoeflich NEAR TERM...OHara SHORT TERM...DeSilva/Hoeflich LONG TERM...DeSilva/Hoeflich AVIATION...DeSilva/OHara MARINE...DeSilva/OHara TIDES/COASTAL FLOODING...WFO PHI