Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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358 FXUS61 KPHI 292005 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 405 PM EDT Thu Sep 29 2016 .SYNOPSIS... Low pressure to the west will gradually move northeast toward the Great Lakes and weaken through Sunday. It will continue to slowly move eastward by Tuesday and bring a cold front through the region. Several other waves of low pressure will move around the larger low and unsettled weather will prevail. High pressure builds to our north for Tuesday into Wednesday. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... **stormy** Please do not estimate the power of this event for tonight and Friday morning! A strong easterly gale together with a pwat axis of almost 2 inches and max inflow almost coincidentally aligned nw-se through De BAY this evening and crossing normal to the coastal front or inverted trough developed by the cold air damming of the past 24 hours, will result in considerable flooding, both freshwater and tidal. Along and north of I-78...periods of rain and drizzle FCST basis: 50/50 blended 12z/gfs/nam mos. Thunder probably south and east of PHL as per the modeled negative SWI. FFA expanded into SNJ. EC is probably going to be correct with max rainfall from this entire event in our area. We are thinking storm totals widespread 3-6" delmarva with isolated 1 foot or even more over Sussex County DE. For the new watch area...widespread 2-4 expected with at least isolated 6+ close to DE Bay and the Atlantic coast. When i see EC synoptic scale qpf of 6"...my mind thinks potential 9. I`m not saying 9 but if the EC pans out...highly efficient rains with embedded convection can yield more than model guidance. We realize this is the only model guidance with this much qpf. We also realize that model guidance has been focused west of our area and we`re realizing quite a bit more than modeled. Wind: NPW may not have large enough areal coverage into central DE and will rereview by 6 PM. Coastal flood: It appears a serious situation is developing for Cape May and Sussex county DE where a moderate coastal flood event appears locked in. The long duration of strong onshore winds (gale gusts, now almost 24 hours) builds the waters in the back bays, sometimes more than the ocean front. Follow the advice of local officials. RER`s already GED and will update this late today and again at 1 am. Dual pol STA looks much better than the legacy STP at DOX and DIX for the Delmarva (DOX returned to service early yesterday afternoon, missing the morning heavy rain that occurred MD e shore). That means adding 70 to 90% to LEGACY output on the DELMARVA should be helpful/useful reality. 9.6 max so far...isolated in southern DE---HARBESON...more general 4-5 inchers other parts of the Delmarva. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... Heavy rains shift north during the day as the inflow and pwat axis shift north. Heavy rains near and north of I-78 of shorter duration, so no flood watch there. Cool and drizzly in the wake of diminishing wind and rain. 50 50 blended 12z/29 GFS/NAM MOS guidance. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... Unsettled weather continues to be forecast for much of the extended period, especially the end of this week into the weekend. The persistent upper low to the w will gradually will and move n and ewd. Various different disturbances will move around this low, and these individual features are difficult to time at best. So unsettled wx is expected Sat and again on Sun, there shud be more dry than wet periods and Sun will be drier than Sat, there will still be lingering precip and clouds into the weekend. The upr low finally crosses thru New Eng late Mon into Tue and any last vestiges of precip shud go with it. There cud be some precip on Mon, but again, small chcs. Tue cud end up being a decent day then by midweek the global mdls have divided themselves into 2 camps, a faster and slower camp. If the faster camp is correct we could...repeat could (also could not) have impacts from tropical storm Matthew by mid or late week. If the slower camp is correct, then any potential impacts would be much later. There are still a lot of differences in the mdls wrt to both track and speed of the sys. Please see latest NHC advisories. && .AVIATION /20Z THURSDAY THROUGH TUESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Through tonight...MVFR cigs variable IFR conditions in showery rains...some of that rain will be heavy. e-ne winds gust 20-30 kt at times, except 35-40 kt vcnty ACY. Iso thunder possible but not in the TAF attm due to low confidence. Friday...MVFR CIGS variable IFR conditions in stratus/periods of rain-drizzle. East to northeast winds are expected to gust 20-30 knots for much of the area Friday, with the strongest winds near the coast. Winds diminish during the afternoon. OUTLOOK... Fri night-Sat night...A prolonged period of MVFR or IFR conditions. Some SHRA expected to affect the TAF sites through the period. Moderate confidence. Sun-Mon...Some improvement, possibly to VFR. Low chc SHRA. Moderate confidence. && .MARINE... GLW continued with verification of gales already most areas. Only upper DE Bay waters have not yet verified and they may not til late today. Extended GLW a few hours and its all posted. Waves heights 8 to 14 ft throughout through Friday morning slowly subsiding late Friday. Outlook... Fri night-Sat...Gale warning has been extended into overnight Friday night for the northern waters and could be extended further. Elsewhere, conds will gradually decrease into Saturday, but a backend SCA is likely before conds drop below. Sat night-Mon...Wind and seas expected to drop below SCA criteria Sat night or early Sun mrng and remain there thru Mon. RIP CURRENTS... There is a high risk for the formation of dangerous rip currents along the NJ shore and the DE beaches today. Wave heights along the coasts 5 to 9 feet. Friday...Mount Holly`s last day of our daily 530am surf zone forecast this year...probably high risk due to residual heavy surf DE and ongoing easterly gale NJ. We`ve had a complication in the HIGH RIP headline (double headline), so we hope to clear this up at 630 PM. && .HYDROLOGY... Thinking that guidance is constantly modeling max rainfall far too far west. The increasingly ely inflow at the sfc this evening combined with being closer to the sbli subzero and constant instability aloft through Friday and increasing 850 inflow to -4SD as well as growing pwat axis to 2" by Friday morning as well as the 12z ECMWF favoring the coastal front has resulted in an expansion of the FFA expanded into SNJ. EC is probably going to be correct with max rainfall from this entire event in our area. We are thinking storm totals widespread 3-6" delmarva with isolated 1 foot or even more over Sussex County DE. For the new watch area...widespread 2-4 expected with at least isolated 6+ close to DE Bay and the Atlantic coast. When i see EC synoptic scale qpf of 6"...my mind thinks potential 9. I`m not saying 9 but if the EC pans out...highly efficient rains with embedded convection can yield more than model guidance. We realize this is the only model guidance with this much qpf. We also realize that model guidance has been focused west of our area and we`re realizing quite a bit more than modeled. FFA. RER`s already GED and will update this RER later today and add ACY PHL ILG records by 5PM in the climate section. Dual pol STA looks much better than the legacy STP at DOX and DIX for the Delmarva (recall DOX came back on line early yesterday afternoon, missing the Wednesday morning heavy rain that occurred on parts of MD`s eastern upper shore). that means add 70 to 90% to LEGACY out put on the DELMARVA should be helpful. 9.5" max (isolated in s DE), mostly 4`s and 5`s, so far. 00z/29 ECMWF 48 hr max rainfall about 5" Md E shore. 12z/29 ECMWF 24 hr max rainfall through 12z Friday, 6" near Cape May. && .TIDES/COASTAL FLOODING... It appears a serious situation is developing for Cape May and Sussex county DE where a moderate coastal flood event appears locked in. The long duration of strong onshore winds (gale gusts, now almost 24 hours) builds the waters in the back bays, sometimes more than the ocean front. Follow the advice of local officials. Otherwise advisories continue as previously forecast today. Last evening ACY was a touch into flood at 712PM (6.35 MLLW with threshold 6.3). This morning Atlantic City NOS registered 6.6Ft MLLW or .3 ft over the threshold. This morning Lewes DE registered 6.6` MLLW (threshold 6.3), Cape May 7.15 ft (threshold 7 feet MLLW) Since tonight`s high tide cycle is higher than that of this morning, and inflow should be stronger, flooding will be worse...probably half a foot to a foot deeper, and expect reaching MDT threshold s NJ and De Atlc shores. The following two high tide cycles Friday will probably endure minor tidal inundation flooding, especially NJ. Additionally...waves this morning were at least 7 to 8 feet on the coast (BTHD1) and may grow to 10 feet tonight. This could add splashover wave runup problems to the lowlands. && .CLIMATE... September will be/is a top 10 warmest month through most of our forecast area, for the 3rd consecutive month! Also September will be/is enjoying a second consecutive top 5 warmest month in the period of record for PHL and ABE. We`ve run the actual numbers through the 28th, then added the forecast high/low for 29th and 30th. Philadelphia: Expect a 73.8 degree average or about 5 degrees above the monthly normal of 69.1. This will be a #4 or #5 warmest September on record for Philadelphia. Philadelphia September average temperature rankings 75.4 -1881 74.5 -2015 74.1 -1931 74.1 -1930 73.8 -2005 and 2016 #4 (small chance PHL avg will be 73.7 or #5 ranking) 72.9 -2010 72.9 - 1921 Philly ranked #7 warmest July followed by a warmest ever August in the POR dating back to 1874. Atlantic City: Expect a 71.2 degree monthly average temperature, or 4 degrees above the monthly normal of 67.2. This would equate to an 8th warmest September in the period of record dating back to 1874. Atlantic City recorded a #7 warmest July and then a warmest ever August. 73.3 - 1961 72.8 - 1881 72.3 - 1931 and 1930 71.7 - 1921 71.6 - 2015 71.5 - 1933 71.3 - 2005 71.2 - 2016 #8 71.0 - 2010 70.6 - 2011 and 1906 Allentown: Expect a monthly average of 69.4 degrees, or 5.5 degrees above the monthly normal of 63.9 and a 4th warmest September on record. Allentown ranked 8th warmest July and #2 warmest August in the period of record. 70.8 - 1961 70.3 - 1980 69.7 - 2015 69.4 - 1931 and 2016 (small chance Allentown will rank #5 at 69.3 degrees) 68.7 - 2005 Daily rainfall records for September 29 where there is maybe a small chance of exceeding: PHL 1.87 1963 ILG 1.97 1963 GED 1.35 2015 RDG 3.55 1934 && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Flash Flood Watch through Friday afternoon for PAZ070-071. NJ...Coastal Flood Warning until 1 AM EDT Friday for NJZ020>027. High Rip Current Risk through Friday afternoon for NJZ014- 024>026. Flash Flood Watch through Friday afternoon for NJZ016>027. Wind Advisory until 6 AM EDT Friday for NJZ020-022>027. Coastal Flood Advisory until 2 AM EDT Friday for NJZ016. Wind Advisory from 11 PM this evening to noon EDT Friday for NJZ013-014. Coastal Flood Advisory until 1 AM EDT Friday for NJZ012>014. DE...Coastal Flood Warning until 1 AM EDT Friday for DEZ002>004. High Rip Current Risk through Friday afternoon for DEZ004. Flash Flood Watch through Friday afternoon for DEZ001>004. Wind Advisory until 6 AM EDT Friday for DEZ003-004. Coastal Flood Advisory until 2 AM EDT Friday for DEZ001. MD...Flash Flood Watch through Friday afternoon for MDZ008-012-015- 019-020. MARINE...Gale Warning until noon EDT Friday for ANZ452-453. Gale Warning until 2 AM EDT Saturday for ANZ450-451. Gale Warning until 8 AM EDT Friday for ANZ454-455. Gale Warning until 6 AM EDT Friday for ANZ430-431. && $$ Synopsis...Nierenberg Near Term...Drag 405 Short Term...Drag 405 Long Term...Nierenberg Aviation...Drag/Nierenberg 405 Marine...Drag/Nierenberg 405 Hydrology...405 Tides/Coastal Flooding...405 Climate...

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