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Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
Issued by NWS Mt. Holly, NJ
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030 FXUS61 KPHI 160804 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 404 AM EDT Fri Aug 16 2024 .SYNOPSIS... Weak high pressure moves offshore by later today, then a cold front slowly works its way across our region Sunday night before shifting offshore during Monday. Meanwhile, Hurricane Ernesto will track well east of our region over the weekend. High pressure builds in from the west later Tuesday through Thursday. && .NEAR TERM /THROUGH TONIGHT/... Broad high pressure moving offshore will bring us a dry end to the work week before the next low pressure system begins to approach the region tonight. Temperatures early this morning are in the mid 60s across much the area with a few spots in the heart of the urban corridor remaining above 70 and higher elevations dipping below 60. Skies are again mostly clear with light to calm winds. Temperatures are forecast to fall into the low 60s across most of the region though the urban corridor is expected to remain in the upper 60s. We are again seeing indications this morning of the formation of some valley fog/patchy ground fog, but again, this should burn off relatively quickly after sunrise. For the daytime hours today, temperatures will be in the upper 80s to near 90 across most of the area (a few upper 70s remaining sprinkled in at the coast and higher elevations) as southerly flow returns to the region with the high sliding offshore. While the center of the surface high is drifting away, the arrival of the upper level ridge will increase subsidence and should keep the entire area dry through the day today. The ridge then passes offshore later this evening into tonight. With the departure of the upper-level ridge and surface high, the next low pressure system will then begin to approach our region tonight. Guidance maintains a slightly slower progression so most of the area should stay dry tonight and any areas that do see some widely scattered showers, likely won`t see them until well after midnight tonight. PoPs 20-40% for the western third of the region (increasing from east to west) with lower PoPs everywhere else. With increasing clouds and continued light southerly winds, lows look to be in the upper 60s to near 70 across most of the region. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... Showers and some thunderstorms increase during the weekend as a slow moving system arrives from the west. As low pressure moves into the eastern Great Lakes on Saturday, another shortwave will slide out ahead of it, resulting in showers and some thunderstorms increasing by later Saturday afternoon and night. Southerly will result in a humid air mass as dew points increase into the upper 60s to low 70s Saturday then into the lower to perhaps mid 70s on Sunday. Given the precipitable water values of around 2 inches, locally heavy rain will occur with any heavier convective cells especially along and north/west of I-95. The coastal areas may remain dry during much of Saturday. While some convective may attempt to organize into a few small clusters across mainly parts of our western zones, the severe weather risk looks to mainly be to our west and southwest where there is a Marginal Risk (level 1 out of 5). As we go through Sunday, additional showers and thunderstorms are expected especially in the afternoon and evening as increasing forcing for ascent overspreads the region and a cold front starts to arrive. The available moisture, with precipitable water values around 2 inches, will once again lead to potentially locally heavy rain. As the front gradually works its way across our area later Sunday, a secondary low develops along it in the vicinity of our area. This may assist in focusing a cluster of showers/thunder with locally very heavy rain. As a result, the flash flooding risk has increased some for Sunday afternoon and evening from about the urban I-95 corridor to the north and west (Slight Risk, level 1 out of 4, for excessive rainfall leading to flash flooding for parts of our area). While the deep-layer shear is forecast to be on the weaker side, enough instability along with steepening low-level lapse rates may result in an isolated severe thunderstorm risk (Marginal Risk, level 1 out of 5) with locally strong winds the main threat, especially if some convective cores become strong enough to promote more efficient downdraft winds due to water loading. While PoPs for measurable rainfall are included in the region for the entire weekend, it is not expected to be a washout and the greatest showers and some thunderstorms should be mostly each afternoon and evening. In addition, Hurricane Ernesto will track northward with its center remaining several hundred miles east of our area, and this will keep the associated moisture maximum also out to sea. Therefore while there will be no direct impacts to our area from the hurricane, larger swells will be driven into the coast resulting in rough surf conditions and there will also be dangerous/life-threatening rip currents. && .LONG TERM /MONDAY THROUGH THURSDAY/... Summary...Some showers and thunderstorms Monday, then improving conditions along with it becoming noticeably cooler and less humid. Synoptic Overview...An upper-level trough remains across the East however this is forecast to weaken some with time. At the surface, a cold front is forecast to be shifting offshore Monday, then a secondary cold front arrives during Tuesday. An area of high pressure builds eastward later Tuesday and settles over our area Wednesday into Thursday. For Monday...An upper-level trough will continue to overspread the East, and this will drive a cold front offshore of our area. While a humid air mass will continue, some lowering of the high dew points is expected to occur late in the day and especially at night. Forcing for ascent with the arriving trough and slowly exiting front will result in some additional showers and thunderstorms especially in the afternoon and early evening. Plenty of moisture in place will once again provide the potential for some locally heavy rain. For Tuesday through Thursday...The upper-level trough is forecast to remain over the East, although it may weaken some with time. Some guidance has indicated the trough becomes reinforced Tuesday, however some of that same guidance has now shifted this more up into New England. A secondary cold front may move through from the northwest Tuesday, and while this looks to be weak at this time kept in slight chance PoPs (20 percent) for possible isolated showers. Meanwhile, surface high pressure centered near the Midwest tied to a ridge builds toward our area later Tuesday, then it should settle over our area Wednesday into Thursday. A noticeably cooler and less humid air mass is forecast to continue to advect into our area, with most of the area topping out into the 70s both Tuesday and Wednesday and then perhaps a touch warmer on Thursday. && .AVIATION /08Z FRIDAY THROUGH TUESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Early this morning...VFR with some passing clouds. Winds light and variable to calm at times. High confidence. Today...VFR with some scattered cumulus clouds and building cirrus. Winds light in the morning becoming S-SSW around 5-10 kts in the afternoon. Sea breeze at KMIV/KACY after 18-20Z may lead to a subtle wind shift to the SSE. High confidence on prevailing VFR conditions. Tonight...VFR conditions expected with increasing mid-level clouds, particularly after 06Z. An isolated shower may approach KRDG/KABE after 09Z. SSE winds around 5 knots or less. High confidence on prevailing VFR conditions. Outlook... Saturday and Sunday...Times of sub-VFR due to showers and some thunderstorms, some with locally heavy rain, especially each afternoon and evening. Some areas of stratus possible. Monday...Times of sub-VFR with some showers and thunderstorms, especially in the afternoon and evening. Tuesday...VFR. && .MARINE... No marine headlines are anticipated through the day today. For tonight, a Small Craft Advisory remains in effect for Atlantic Ocean coastal waters beginning at 10 PM EDT. Seas initially 1-2 feet this morning building to 2-4 feet later this afternoon. Seas begin to exceed 5 feet late this evening and continue to build towards 5-7 feet by late tonight. Winds of 5-10 kts with gusts around 15 knots expected throughout the period. Outlook... Saturday and Sunday...A Small Craft Advisory now in effect through Sunday night for the New Jersey and Delaware Atlantic coastal waters for seas 5 to 7 feet due to larger swells from distant Hurricane Ernesto. The conditions on Delaware Bay are anticipated to stay below Small Craft Advisory criteria. Monday...Small Craft Advisory conditions linger as seas slowly subside on the Atlantic coastal waters. The conditions on Delaware Bay are anticipated to stay below Small Craft Advisory criteria. Tuesday...The conditions are anticipated to be below Small Craft Advisory criteria. Rip Currents... Today...South winds will increase to 10 to 15 mph with occasional gusts up to 20 mph in the afternoon. Breaking waves will average 2 to 3 feet with a long period swell of 12-14 seconds developing. Given the increasing period, wave height, and winds, there is a MODERATE risk for the development of dangerous rip currents for the Jersey Shore and Delaware Beaches. For Saturday and Sunday, Hurricane Ernesto will track well east of our region. However, larger swells arriving from this storm and breaking into the surf zone will result in very dangerous rip currents at the Jersey Shore and at the Delaware Beaches. Breaking waves could reach as high as 5 to 8 feet. Some beach erosion is possible. The high risk of rip currents could linger into early next week as well. For specific beach forecasts, visit weather.gov/beach/phi && .TIDES/COASTAL FLOODING... With long period swells and rough seas/surf expected to arrive this weekend from distant Hurricane Ernesto coinciding with an approaching full moon on Monday, at least some spotty minor coastal flooding is anticipated to develop along the Atlantic coasts of New Jersey and Delaware, Delaware Bay, and the tidal Delaware River. The primary high tide cycles of impact will be evening to nighttime high tides, perhaps beginning as early as Saturday in some areas. As long period swells persist and astronomical high tides increase Sunday and Monday, more widespread minor coastal flooding may be possible with the evening to nighttime high tides those days. Anyone with interests in these areas that are susceptible to minor coastal flooding should monitor the latest forecasts and remain alert for any advisories that may be issued in future updates as confidence in the forecast increases. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...High Risk for Rip Currents from late tonight through Sunday evening for NJZ014-024>026. DE...High Risk for Rip Currents from late tonight through Sunday evening for DEZ004. MD...None. MARINE...Small Craft Advisory from 10 PM this evening to 6 AM EDT Monday for ANZ450>455. && $$ SYNOPSIS...Gorse NEAR TERM...AKL SHORT TERM...Gorse LONG TERM...Gorse AVIATION...AKL/Gorse MARINE...AKL/Gorse/Staarmann TIDES/COASTAL FLOODING...Staarmann