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Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
Issued by NWS Mt. Holly, NJ
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831 FXUS61 KPHI 150758 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 358 AM EDT Thu Aug 15 2024 .SYNOPSIS... Weak high pressure over the area moves offshore late Friday, then a cold front slowly works its way across our region Sunday night before moving offshore on Monday. Meanwhile, Hurricane Ernesto will track well east of our region during the weekend. High pressure builds in from the west later Tuesday through Wednesday. && .NEAR TERM /THROUGH TONIGHT/... Broad high pressure will continue to be the dominant feature through the near term forecast period but it will be weakening and slowly drifting eastward through this timeframe. Temperatures early this morning are in the upper 50s to mid 60s across the area with a few spots in the heart of the urban corridor remaining near 70. Skies are clear with light winds which is resulting in some valley fog/patchy ground fog, particularly in northwest New Jersey. The valley fog may extend southward into the Lehigh Valley as we head towards dawn this morning. For the daytime hours today, temperatures will be in the mid 80s across most of the area (some upper 70s at the coast and higher elevations). With the center of the high slowly drifting to the east, winds look to be even lighter today compared to yesterday (less than 10 mph for most locations). A sea breeze looks to again develop this afternoon, and with the light flow, may make it into the I-95 corridor by this evening. Skies look to be partly to mostly sunny as some cumulus develops in the afternoon hours. Some mid and upper-level shortwave energy may once again help spark a few isolated showers or a thunderstorm this afternoon/evening, most likely in northern New Jersey as well as along the sea breeze in southern New Jersey. With cumulus and any convection once again rapidly dissipating after sunset, conditions tonight will be quite similar to early this morning. Surface high pressure becoming centered near/south of the region will lead to mostly clear skies and light to calm winds. Lows mainly in the 60s expected. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... Turning more humid to start the weekend and also an increase in the chances for showers and thunderstorms. Dangerous rip currents and surf are expected due to distant Hurricane Ernesto. A closed low centered over the Midwest and Upper Great Lakes Friday will slowly shift eastward through Saturday night. Some weak ridging in the mid levels Friday is forecast to slide across our area, which will support a weak area of high pressure. This along with a slower eastward advancement of the closed low results in a dry Friday, at least during the daytime hours. While some clouds are expected to increase, a slower arrival of the aforementioned trough should result in more sunshine hanging on longer Friday. The low-level flow turns more southerly Friday and this will start to advect more low- level moisture into our area, however a warm front is forecast to still be to our west and southwest. As a result, a very warm Friday afternoon is forecast with many areas getting into the upper 80s (some spots could touch 90 degrees). Ample boundary layer heating may lower the dew points some during peak heating, then these start to inch up through the 60s at night. Showers and thunderstorms well to our west during the day Friday are forecast to arrive into at least our western zones during the evening and spread eastward overnight. This is also within a moisture plume as precipitable water values increase to 1.5-2.0 inches. Some of this activity however may dissipate with an eastward extent given lowering instability and it outrunning the main forcing for ascent. As we go through Saturday, a humid air mass is forecast to overspread our area as a warm front arrives and boosts the dew point to 70 degrees or above. An initial band of convection looks to push across our western and northern areas with this possibly extending father south. The precipitable water values are forecast to be around 2 inches, and this will set the stage for locally heavy rain (possibly localized flash flooding) associated with the convection. There may be multiple rounds of showers and some thunderstorms (some possibly organized into clusters), with an increase especially later in the afternoon and evening as height falls overspread our area with the incoming upper-level trough. The intensity of the thunderstorms will depend on the extent of the cloud cover (instability), and the shear magnitude which looks to be on the weak side in our area. Weaker mid level lapse rates may also hold down the instability some. Overall though as of now, an isolated risk for severe thunderstorms is mainly to our west and southwest. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... Summary...Some showers and thunderstorms continue into early next week as a cold front works its way across our area and then offshore. Hurricane Ernesto remains well offshore into Monday, although dangerous surf and rip currents will continue for a while longer. Synoptic Overview...An upper-level trough shifts eastward and settles across the Northeast and Mid-Atlantic regions. This trough may be reinforced around mid-week. At the surface, low pressure tracks to our north Sunday into Monday and a cold front then crosses our area Sunday night into Monday. A weak surface low may develop across our area Sunday night into Monday along the occluded front/triple point. A secondary cold front may move through during Tuesday, then high pressure gradually arrives later Tuesday through Wednesday. For Sunday and Monday...Surface low pressure tracks to our north with a trailing cold front working its way across our area Sunday night into Monday. As the trough axis gets much closer, a secondary low may develop along the occluding front/triple point as it crosses our area. A humid air mass (dew points into the lower 70s) will remain in place ahead of the cold front and this keeps the precipitable water values at around 2 inches. Forcing for ascent with the incoming trough and front/low will result in showers and some thunderstorms especially each afternoon and evening. A locally heavy rain risk is present, although the flash flooding potential at this time looks to be on the low side. The intensity of thunderstorms is less certain as this will depend on the extent of the showers, cloud cover and magnitude of the instability. The PoPs increase with these peaking mostly each afternoon and evening. This trough will keep Hurricane Ernesto and its associated moisture maximum well east of our area. For Tuesday and Wednesday...The upper-level trough is forecast to remain over the East, with it possibly being reinforced some into Wednesday. While the initial cold front is well offshore, a secondary cold front may move through from the northwest sometime during Tuesday. Meanwhile, surface high pressure centered near the Midwest tied to a ridge should build toward our area. While a shower or thunderstorm cannot be ruled out with the presence of the trough aloft and the incoming secondary cold front, the chances look reduced given additional drying and surface high pressure building more into our area. Dew points are forecast to lower and the temperatures also cool. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Early this morning...VFR/SKC. Winds 5 kts or less, favoring a N to NW direction. Some sites (e.g., KMIV/KACY) will see winds go light and variable for the period. High confidence. Today...VFR. Winds 5 kts or less, favoring a N to NW direction, or remaining light and variable through much of the day. A sea- breeze will likely once again develop causing a SE/SSE wind shift for at least KMIV/KACY beginning around 18-20Z. Sea-breeze my end up penetrating further inland toward I-95 given the prevailing background flow. High confidence overall, moderate confidence in sea- breeze timing. Tonight...VFR with mostly clear skies. Winds light and variable to calm at times. High confidence. Outlook... Friday through Sunday...Times of sub-VFR conditions due to showers and some thunderstorms some of which could be locally heavy, starting Friday night into Saturday. Monday..Some additional showers and thunderstorms around. && .MARINE... No marine headlines are anticipated through tonight. Winds around 5- 10 kts with seas around 1-2 feet. Fair weather. Outlook... Friday...The conditions are anticipated to be below Small Craft Advisory criteria. Saturday and Sunday...Small Craft Advisory conditions especially for the Atlantic coastal waters, mainly for elevated seas due to larger swells from distant Hurricane Ernesto. Monday...The Small Craft Advisory conditions may continue as seas/swells slowly subside. Rip Currents... Today...Light north winds will become south 5 to 10 mph in the afternoon as sea breezes develop. Breaking waves will be around 1 foot with a 9 second period. Therefore, there is a LOW risk for the development of dangerous rip currents at the Jersey Shore and at Delaware Beaches. Friday...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. With winds more parallel/slightly offshore, there is a LOW risk for the development of dangerous rip currents for 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. For specific beach forecasts, visit weather.gov/beach/phi && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ SYNOPSIS...Gorse NEAR TERM...AKL SHORT TERM...Gorse LONG TERM...Gorse AVIATION...AKL/Gorse MARINE...AKL/Gorse