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Forecast Discussion for New York City/Upton, NY
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975 FXUS61 KOKX 210848 AFDOKX Area Forecast Discussion National Weather Service New York NY 448 AM EDT Sun Jun 21 2026 .WHAT HAS CHANGED... Slight risk of excessive rainfall has shifted south to only include NE NJ and the NYC metro with a marginal risk elsewhere. && .KEY MESSAGES... 1) Isolated showers and a rumble of thunder possible this afternoon, mainly across the interior. 2) Heavy rainfall Monday afternoon into Monday night will bring the potential of urban and poor drainage flood impacts, as well as localized flash flooding. 3) There is a marginal risk for severe thunderstorms in the vicinity of NE NJ and the NYC metro Monday afternoon and evening. 4) Showers and thunderstorms are possible Thursday and Friday. && .DISCUSSION... .KEY MESSAGE 1... The passage of a shortwave this afternoon may develop isolated showers, mainly across the interior. Instability based on forecast soundings is relatively shallow, but there is enough present above the freezing level to support potential of a few lightning strikes. Dry subcloud layer also supports locally gusty winds in any of the isolated showers. Any shower development this afternoon will quickly dissipate this evening as the shortwave energy passes to the east. .KEY MESSAGE 2... Developing low pressure over the Plains today will quickly move east towards the area tonight. An associated warm front will approach Monday morning and set up near the region Monday afternoon and evening. The system has the potential to bring periods of moderate to locally heavy showers and thunderstorms Monday afternoon into Monday night. The modeling is continuing to struggle with the placement of the warm front and axis of heaviest rainfall. Some of this uncertainty is tied to convective errors with timing/strength/location of the system. High resolution models are starting to come into range, but offer little agreement on the evolution of where the heaviest rainfall/convection will ultimately occur. Despite the aforementioned uncertainties, the synoptic environment supports deep moisture convergence in the vicinity of the warm front/low pressure. Models continue to signal potential of precipitable waters ranging from 1.75-2.25", especially Monday afternoon and evening. Forecast soundings also indicate a fairly deep warm cloud layer with freezing levels progged around 12-14kft. This is a good indication of efficient warm rain processes and supports the potential of heavy downpours. The greatest potential for heavy rain appears to be late Monday afternoon into the first half of Monday night when there will likely be a combo of deep moisture pooling in the vicinity of the warm front and support aloft from the approach of a middle level shortwave. Some of the global models also signal amplification of an upper jet over Northern New England, which may help with heavy rain development Monday evening. Average basin rainfall amounts continue to range from 1-2 inches with locally higher amounts possible. Rainfall rates may reach 1- 1.5"/hr and could locally reach 2"/hr. This supports the potential for urban/poor drainage flooding and mainly a localized flash flood risk. The main concern appears to be across the heavily urbanized NE NJ and the NYC metro where these rainfall rates can produce urban flash flooding. The risk for river and stream flooding is low as recent dry conditions have led to fairly high flash flood/headwater guidance. Around 2 inches in an hour and 2-3 inches in 3 hours is needed for flash flooding across NE NJ. Across the interior and Southern CT, 3 inches in an hour and 4 inches in 3 hours is needed to reach minor flood stage on rivers/streams. Cannot completely rule out some of the flashier streams reaching minor flood stage based on the 3 hour guidance. In collaboration with WPC and neighboring offices, the slight risk for excessive rainfall has been scaled back to mainly include urban NE NJ and the NYC metro in our CWA. Elsewhere, the risk is marginal, which is supported by the recent dry conditions, high flash flood/headwater guidance, and expectation that these areas can handle the heavy rain potential compared to the urban corridor. There has been a trend in the last 24 hours to linger showers, potentially embedded thunder late Monday night into early Tuesday. This is due to a slower timing of the low pressure, which may not completely move east of the area until Tuesday afternoon. The heavy rain/flooding threat should diminish after midnight, but a few locally heavy downpours could linger across Long Island/SE CT into the first half of Tuesday morning. .KEY MESSAGE 3... Confidence in severe thunderstorms Monday afternoon and evening continues to be low at this time. Instability looks to be maximized to the south of the area across the Middle Atlantic. However, the warm front nearby or over the area could be a mechanism to support isolated severe thunderstorm development. Currently, this potential looks to be mainly across NE NJ, NYC metro, and western Long Island where SPC has continued with a marginal risk. The main threat is from damaging wind gusts and an isolated tornado due to low level directional shear and proximity of the warm front. The severe threat could increase and cover more of the area if the instability and warm front were to trend north. .KEY MESSAGE 4... Southwest flow aloft looks to set up by late Thursday into Friday ahead of the next shortwave/cold front. This would help to trigger the potential for showers and a few thunderstorms. Confidence is starting to increase that the greatest potential ends up on Friday when the shortwave axis is currently progged to move across the area. Any severe/hydro impacts are uncertain at this time since this is 5-6 days out. && .AVIATION /09Z SUNDAY THROUGH THURSDAY/... Weak high pressure will be in place through tonight. Mainly VFR. Some showers with brief MVFR conds are possible this afternoon into early evening. Can`t rule out thunder as well, but not enough probability to include in TAFs. W winds under 10kt bcmg W-SW around 10kt later this morning. Sea breezes probable for some of the coastal terminals late this morning into the afternoon. ...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty... Shifts to SW, then S may be off by an hour or two at KJFK. Sea breeze potentially does not reach KLGA, which would then lead to winds remaining westerly all afternoon. .OUTLOOK FOR 06Z MONDAY THROUGH THURSDAY... Late tonight: VFR. Monday-Monday night: VFR in the morning, lowering to MVFR and lower in the afternoon with rain. Rain and IFR at night. Chance of a thunderstorm as well both afternoon and night. SE gusts around 20kt possible. Tuesday: IFR with lingering rain/showers to start. Improving to MVFR in the afternoon, then VFR late in the day. Still a chance of a shower during the afternoon. Wednesday: VFR. Thursday: VFR in the morning. Chance of MVFR in the afternoon with potential showers/TSTMs. Southerly wind gusts 15-20 kt possible in the afternoon into evening. Detailed information, including hourly TAF wind component forecasts, can be found at: https:/www.weather.gov/zny/n90 && .MARINE... Winds and seas will be below SCA levels through Monday morning. the next chance for SCA conditions will be late Monday into Monday night when winds and seas ramp up, especially on the ocean. Seas subside Tuesday morning, with high pressure likely keeping conditions below SCA levels from late Tuesday through Thursday. Rip Currents: The rip current risk is moderate at SE Suffolk beaches where a 3ft S swell @ 8 seconds likely persists. The rip current risk is low for the rest of the ocean beaches with a 2ft S swell @ 8 seconds. On Monday, the rip current risk is moderate, especially in the afternoon and evening with increasing S flow and wind waves 3-4 ft. The risk could become high late in the day for western beaches if higher winds and wind waves occur earlier than currently expected. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ DISCUSSION...DS AVIATION...JC MARINE...DS |
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