Area Forecast Discussion

WHAT HAS CHANGED

Severe Thunderstorm Watch in effect until 12 am this evening for NYC, northeast NJ, and the LoHud Valley. Damaging wind gusts are the primary threat from these storms.

KEY MESSAGES

1) A window remains for severe thunderstorms and localized flash flooding through this evening. Additional strong to severe thunderstorms are possible once again late Friday afternoon and evening.

2) Hot and humid conditions continue through Friday and a Heat Advisory remains in effect for much of the region.

3) Potential for more strong to severe thunderstorms Sunday late afternoon and evening.

4) There is the potential for minor coastal flooding this weekend.

DISCUSSION

.KEY MESSAGE 1... Severe Thunderstorm Watch in effect until midnight local time for western half of the forecast area, including NYC.

Line of showers and thunderstorms continues to work east into Eastern PA and Upstate NY as a shortwave trough moves into the Northeast. The line has become more organized with embedded severe thunderstorms, but should start to wane in intensity as it reaches a diurnally stable air mass after dark. Can't rule out damaging wind gusts along and ahead of the line as it enters the forecast area by 9 or 10 pm, before the activity weakens in a more stable air mass along the coast.

For Friday, it may largely be a repeat of Thursday with some conditional instability building during the afternoon hours with the heat and humidity. The main difference will be a more potent upper level short wave moving through the region and a weak surface cold front that could provide some more lift across the region to support storm development. However, like today, there is a lag in the timing of this feature and storms may not arrive until the very late afternoon into the evening hours, as instability will wane across the region, which will directly impact storm coverage. Therefore, have trended down storm chances but a strong to severe storm threat remains possible.

KEY MESSAGE 2

This afternoon, temperatures across the region have reached the upper 80s and lower 90s with dew points in the 70s. This has resulted in heat index values in the upper 90s and lower 100s. These hot conditions will subside this evening with some shower and storm activity developing across the region and the loss of peak diurnal heating.

Behind tonight's convective activity, an upper ridge will return north on Friday and allow for similar conditions to today. 850 mb temperatures will surge toward the 20 C mark, translating to surface temperatures in the upper 80s to lower 90s. Moisture across the region will remain elevated with surface dew points in the upper 60s to lower 70s. Together, this will allow for Heat Index Values to be in the mid 90s to lower 100s on Friday. The Heat Advisory remains valid for much of the area through 8 PM Friday.

Temperatures and heat index values will remain muted in the lower to mid 80s for coastal SE CT and Eastern Long Island, and these areas will stay out of the Heat Advisory.

KEY MESSAGE 3

An upper level shortwave trough approaches on Sunday along with an associated cold front at the surface. Most of the day will be sunny and hot with an increasing southerly flow. At this time, afternoon temps in the upper 80s to lower 90s and dewpoints in the lower 60s do not raise a concern for heat hazards.

While it is too far out for specific details, there is at least potential for strong to severe thunderstorms during the late afternoon and evening on Sunday. There is decent agreement among the global models with QPF output along the approaching cold front, along with a tongue of instability stretching into northeast NJ. The SPC has outlined NYC and north and west in a Day 4 slight risk, with the CSU-MLP showing a marginal risk.

KEY MESSAGE 4

With the approach of a new moon astronomical tides will climb some into the weekend. For mainly the southern bays of Queens, western LI, and SW CT minor coastal flood benchmarks may be approached for the Saturday and Sunday evening high tide cycles. The relatively higher chance of minor benchmarks being met or exceeded is for the Sunday evening high tide due to slightly higher tide levels. Coastal flood headlines may be needed in subsequent updates.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

Weak elongated low pressure remains near the region through the TAF period. A cold front approaches from the west Friday afternoon.

VFR outside of SHRA/TSRA.

Line of thunderstorms now just east of KAVP and KMDT at 00Z continues to advance east into the region this evening. Latest timing brings the activity into NYC terminals as early as 2Z, likely closer to 3Z for KLGA and KJFK. MVFR or lower conds and brief wind gusts to 40 kt or greater possible with the line. The convection should begin to weaken as it pushes further east, and any lingering showers should exit the area by 5Z with dry conditions returning throughout. Additional chances for TSRA return Friday afternoon, with PROB30 toward 20-21z thru 2-3Z Sat.

Outside of any convective activity, winds are generally westerly (or more variable) tonight, with speeds around 10 kt for the city terminals, and 5 to 10 kt for most outlying terminals. W to SW winds take shape again with similar wind speeds Friday, gusts to around 20 kt possible in the afternoon.

NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty

Timing of TSRA this evening could be off +/- 1 hr.

Brief gusts to 40+ kt possible with/ahead of the thunderstorms.

Gusts on Friday may initiate sooner than indicated in TAF.

.OUTLOOK FOR 00Z SATURDAY THROUGH TUESDAY...

Friday Night: MVFR or lower possible thru mid evening with chance for showers and thunderstorms. There is potential for some storms to be severe with damaging winds.

Saturday: VFR.

Sunday: Mainly VFR, then slight chance of a shower or thunderstorm with brief MVFR or lower possible late in the day. Showers likely at night with MVFR or lower possible and a slight chance of thunderstorms. Southerly wind gusts 20-25 kt afternoon and evening.

Monday: Mainly VFR. Slight chance of a shower with MVFR possible early for eastern most terminals.

Tuesday: Mainly VFR. Slight chance of a shower or thunderstorm towards evening and at night.

Detailed information, including hourly TAF wind component forecasts, can be found at: https:/www.weather.gov/zny/n90

MARINE

Light flow of 5 to 15 kts is expected through Saturday and Small Craft Advisory headlines are not expected at this time. Winds will be southwesterly through Friday evening before shifting to the northwest behind a cold front.

There is potential for brief Small Craft Advisory conditions Sunday into Sunday night with an increasing southerly flow ahead of a cold front. This will likely be real marginal and mainly for the ocean waters, with 25 kt gusts and 4-5 ft seas.

Rip Currents...

For today, there is a moderate rip current risk with SW winds around 10 kt and surf around 3 ft.

On Friday, a SW flow around 10kt and a 3ft 6s swell from the south will combine to bring a moderate risk of rip currents for southern Nassau and southern Suffolk. The risk for NYC beaches is low, with a bit of a weaker swell. It is marginal overall for all beaches, but RCMOS helped lean towards increasing the risk.

The risk lowers to low on Saturday with a west wind under 10 kt and a lingering 2 ft southerly swell.

CLIMATE

Record High Temperatures:

June 11: KEWR: 96/2000 KBDR: 93/1984 KNYC: 95/1973 KLGA: 96/1984 KJFK: 93/1984 KISP: 93/1973

June 12: KEWR: 97/2017 KBDR: 93/2017 KNYC: 93/2017 KLGA: 96/2017 KJFK: 92/2017 KISP: 91/2017

Record High Minimum Temperatures:

June 11: KEWR: 77/1984 KBDR: 71/2008 KNYC: 78/1984 KLGA: 76/1973 KJFK: 76/1984 KISP: 71/1984

June 12: KEWR: 74/1973 KBDR: 69/1973 KNYC: 76/2017 KLGA: 76/2017 KJFK: 73/1970 KISP: 70/1973

June 13: KEWR: 74/2005 KBDR: 71/2017 KNYC: 77/2017 KLGA: 80/2017 KJFK: 72/2017 KISP: 70/1969

OKX WATCHES / WARNINGS / ADVISORIES

CT...Heat Advisory until 8 PM EDT Friday for CTZ005>010. Air Quality Alert until 11 PM EDT this evening for CTZ009>012. Air Quality Alert from 11 AM to 11 PM EDT Friday for CTZ009>012. NY...Heat Advisory until 8 PM EDT Friday for NYZ067>075-078-080- 176>179. Air Quality Alert until 11 PM EDT this evening for NYZ071>075- 078>081-176>179. NJ...Heat Advisory until 8 PM EDT Friday for NJZ002-004-006-103>108. MARINE...None.