A strong cold front crossed the region during the early morning hours of August 21. High precipitable water and storm motion parallel to the front combined to produce heavy rain that led to flash flooding over parts of Nassau County.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS OKX wrote it up.
A strong cold front crossed the region during the early morning hours of August 21. High precipitable water and storm motion parallel to the front combined to produce heavy rain that led to flash flooding over parts of Nassau County. In Garden City, a trained spotter measured 2 inches of rain.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS New York, NY wrote its last area forecast discussion before the first event at Aug 21, 2:14 AM EST, 46 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NEW YORK NY 314 AM EDT FRI AUG 21 2015 .SYNOPSIS... A COLD FRONT SLOWLY CROSSES THE AREA TODAY AND TONIGHT. THE FRONT WILL DISSIPATE OVER OR JUST EAST OF THE AREA THIS WEEKEND WHILE HIGH PRESSURE BUILDS TO THE NORTH AND WEAK LOW PRESSURE PASSES WELL OFFSHORE. A SLOW MOVING COLD FRONT WILL APPROACH ON MONDAY...THEN PASS THROUGH MONDAY NIGHT INTO TUESDAY. HIGH PRESSURE WILL RETURN FROM TUESDAY NIGHT INTO THURSDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... HEAVIEST RAIN FROM THE SHOWERS AND EMBEDDED THUNDERSTORMS AHEAD OF THE COLD FRONT HAS OCCURRED JUST UPSTREAM AND INTO WESTERN ORANGE COUNTY. WILL ATTEMPT TO DRAW POPS ACCORDING TO SHOWER/TSTM TRENDS AND MESOSCALE GUIDANCE. FRONT SLOWS AND NEARLY STALLS AS UPPER FLOW BECOMES NEARLY PARALLEL. UPPER LIFT PASSES WELL TO THE NORTH AND EAST TODAY...WITH WEAK SUBSIDENCE THEREAFTER. WEAK CONVERGENCE THOUGH ALONG THE FRONT COULD STILL TRIGGER A FEW SHOWERS AND TSTMS THIS AFTERNOON...WITH HIGHEST POPS OBVIOUSLY THIS MORNING AHEAD OF THE FRONT. TOOK A BLEND OF THE MOS...WITH READINGS ABOVE NORMAL BY A FEW DEGREES. THERE IS A MODERATE RISK FOR RIP CURRENT DEVELOPMENT AT THE OCEANFRONT TODAY. && .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/... DRIER AIR DOES BEGIN TO FILTER IN ON THE BACK SIDE OF THE FRONT TONIGHT AND SATURDAY. THEN DEEPER MOISTURE BEGINS TO INCREASE FROM EAST TO WEST SAT NIGHT. SFC HIGH PRESSURE BUILDS TO THE WEST. EASTERN SECTIONS COULD STILL SEE AN ISOLATED SHOWER OR AFTERNOON TSTM...CLOSER TO THE FRONT AND POSSIBLY AIDED BY WEAK VORT ADV ALOFT. IN FACT...THE FRONT MAY RETROGRADE SOMEWHAT AS STACKED LOW PRESSURE REMAINS ANCHORED OVER THE WESTERN ATLANTIC. WARM CONDITIONS PREVAIL WITH A MOS BLEND FOLLOWED. && .LONG TERM /SUNDAY THROUGH THURSDAY/... THE FRONTAL BOUNDARY REMAINS ACROSS THE AREA SUNDAY AS A BROAD LOW PRESSURE AREA WELL OFF THE SOUTHERN MID ATLANTIC SLOWLY LIFTS NORTHWARD...WITH INCREASING HUMIDITY AND CHANCES FOR SHOWERS AND TSTMS THROUGHOUT...ESPECIALLY NEAR WHERE THE WEAKENING BOUNDARY SETS UP WHICH APPEARS UNCERTAIN ATTM. BY MON...THE BOUNDARY WILL HAVE WASHED OUT ENTIRELY AS THE LOW STARTS TO PULL OFF TO THE EAST...AND HIGH PRESSURE BRIEFLY NOSES DOWN FROM NEW ENGLAND...BUT AIR MASS SHOWERS/TSTMS STILL LOOK POSSIBLE ESPECIALLY OVER INTERIOR SOUTHERN CT...THEN ALSO WESTERN SECTIONS BY LATE AFTERNOON AS A COLD FRONT BEGINS TO APPROACH. THIS SLOW MOVING COLD FRONT SHOULD BRING CHANCES OF SHOWERS/TSTMS THROUGHOUT FROM MON NIGHT INTO MUCH OF THE DAYTIME HRS ON TUE. TEMPS FROM SAT THROUGH TUE LOOK TO BE NEAR AVG. HIGH PRESSURE WILL THEN GRADUALLY BUILD IN BEHIND THE FRONT FROM WED INTO THU...WITH ONLY SLIGHTLY COOLER DAYTIME TEMPS BUT NOTICEABLY LOWER HUMIDITY AND NIGHTTIME TEMPS...WITH LOWS IN THE 50S AND 60S. && .AVIATION /07Z FRIDAY THROUGH TUESDAY/... A COLD FRONT MOVES THROUGH THE NYC AREA TERMINALS 11-13Z...THE FRONT THEN SLOWS DOWN AND NEARLY STALLS OVER LONG ISLAND. MOSTLY MVFR WITH SOME IFR IN RAIN MOVING THROUGH. RAIN ENDS IN THE CITY BY SUNRISE. FOR THE CITY AND POINTS WEST...CONDS IMPROVE TO VFR BY NOON...TAKING LONGER FARTHER EAST...WHERE ADDITIONAL SHOWERS COULD OCCUR THIS AFTN WITH DAYTIME HEATING. TSTMS NOT EXPECTED TO PASS DIRECTLY OVER ANY TERMINAL...BUT BEST CHANCE WOULD BE AT KSWF BY 08Z. WINDS PRIMARILY UNDER 10KT...BUT DIRECTIONS...ESPECIALLY AFTER THE COLD FRONT PASSAGE IS LOW T0 MODERATE CONFIDENCE. THERE COULD BE A PERIOD OF A FEW HOURS WHERE WINDS ARE LIGHT AND VARIABLE BEFORE SHIFTING BACK SE MID-LATE AFTN FOR THE CITY TERMINALS. .OUTLOOK FOR 06Z SATURDAY THROUGH TUESDAY... .FRIDAY NIGHT-SATURDAY...VFR. .SATURDAY NIGHT...MVFR OR LOWER POSSIBLE ACROSS CT/LI TERMINALS WITH SHRA. .SUNDAY-TUESDAY...MVFR OR LOWER POSSIBLE WITH A CHANCE OF SHRA/TSRA. && .MARINE... PRESSURE GRADIENT RELAXES WITH WINDS 10 KT OR LESS FORECAST THROUGH TONIGHT ON ALL WATERS. WAVES ARE FORECAST TO REMAIN 4 FT OR LESS ON THE COASTAL OCEAN WATERS. A LONG SE FETCH BETWEEN HIGH PRESSURE EAST OF NOVA SCOTIA AND LOW PRESSURE SLOWLY MOVING NORTHWARD WELL OFF THE SOUTHERN MID ATLANTIC COAST WILL GENERATE SWELLS DIRECTED AT THE COASTAL WATERS...THAT COULD BE AS HIGH AS 5 FT FROM SUNDAY AFTERNOON INTO MON MORNING. && .HYDROLOGY... MORNING URBAN AND POOR DRAINAGE FLOODING IS POSSIBLE LOCALLY IN HEAVIER SHOWERS. ANY ACTIVITY THIS AFTERNOON WILL BE SCATTERED TO ISOLATED IN NATURE. NO SIGNIFICANT WIDESPREAD RAINFALL IS EXPECTED THIS WEEKEND AND THROUGH THE MIDDLE OF NEXT WEEK. HOWEVER...WITH A HUMID AIR MASS AND WEAK FRONTAL BOUNDARY IN PLACE...LOCALLY HEAVY RAINFALL MAY BE POSSIBLE ANYWHERE WITHIN THE AREA DURING TIMES OF PEAK HEATING EACH AFTERNOON FROM SUNDAY INTO TUESDAY. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...NONE. NY...NONE. NJ...NONE. MARINE...NONE. && SYNOPSIS...PW NEAR TERM...PW SHORT TERM...PW LONG TERM...GOODMAN/PW AVIATION...JC MARINE...PW HYDROLOGY...PW
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE NEW YORK NY 316 AM EDT FRI AUG 21 2015 CTZ005>012-NJZ002-004-006-103>108-NYZ067>075-078>081-176>179-220900- NORTHERN FAIRFIELD-NORTHERN NEW HAVEN-NORTHERN MIDDLESEX- NORTHERN NEW LONDON-SOUTHERN FAIRFIELD-SOUTHERN NEW HAVEN- SOUTHERN MIDDLESEX-SOUTHERN NEW LONDON-WESTERN PASSAIC- EASTERN PASSAIC-HUDSON-WESTERN BERGEN-EASTERN BERGEN-WESTERN ESSEX- EASTERN ESSEX-WESTERN UNION-EASTERN UNION-ORANGE-PUTNAM-ROCKLAND- NORTHERN WESTCHESTER-SOUTHERN WESTCHESTER-NEW YORK (MANHATTAN)-BRONX- RICHMOND (STATEN ISLAND)-KINGS (BROOKLYN)-NORTHWESTERN SUFFOLK- NORTHEASTERN SUFFOLK-SOUTHWESTERN SUFFOLK-SOUTHEASTERN SUFFOLK- NORTHERN QUEENS-NORTHERN NASSAU-SOUTHERN QUEENS-SOUTHERN NASSAU- 316 AM EDT FRI AUG 21 2015 THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHERN CONNECTICUT...NORTHEAST NEW JERSEY AND SOUTHEAST NEW YORK. .DAY ONE...TODAY AND TONIGHT. THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY. NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME THAT WOULD MEET NATIONAL WEATHER SERVICE WARNING CRITERIA. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME. && THIS HAZARDOUS WEATHER OUTLOOK PROVIDES A SUMMARY OF POTENTIAL WIDESPREAD HAZARDOUS WEATHER EVENTS THAT MAY REACH NWS WARNING CRITERIA. MOST LONG FUSED NWS WATCHES...WARNINGS AND ADVISORIES IN EFFECT ARE HIGHLIGHTED. PLEASE REFER TO THE LATEST NWS FORECASTS FOR WEATHER NOT MEETING NWS WARNING CRITERIA. ANZ330-335-338-340-345-350-353-355-220900- LONG ISLAND SOUND EAST OF NEW HAVEN CT/PORT JEFFERSON NY- LONG ISLAND SOUND WEST OF NEW HAVEN CT/PORT JEFFERSON NY- NEW YORK HARBOR-PECONIC AND GARDINERS BAYS- SOUTH SHORE BAYS FROM JONES INLET THROUGH SHINNECOCK BAY- MORICHES INLET NY TO MONTAUK POINT NY OUT 20 NM- FIRE ISLAND INLET NY TO MORICHES INLET NY OUT 20 NM- SANDY HOOK NJ TO FIRE ISLAND INLET NY OUT 20 NM- 316 AM EDT FRI AUG 21 2015 THIS HAZARDOUS WEATHER OUTLOOK IS FOR ATLANTIC COASTAL WATERS. .DAY ONE...TODAY AND TONIGHT. THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY. NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME THAT WOULD MEET NATIONAL WEATHER SERVICE WARNING CRITERIA. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME. && THIS HAZARDOUS WEATHER OUTLOOK PROVIDES A SUMMARY OF POTENTIAL WIDESPREAD HAZARDOUS WEATHER EVENTS THAT MAY REACH NWS WARNING CRITERIA. MOST LONG FUSED NWS WATCHES...WARNINGS AND ADVISORIES IN EFFECT ARE HIGHLIGHTED. PLEASE REFER TO THE LATEST NWS FORECASTS FOR WEATHER NOT MEETING NWS WARNING CRITERIA.
The Brookhaven radar (KOKX), 81 km away, was scanning. The volume nearest the first event began at 08:01 UTC.
3 flash flood, 1 heavy rain. Local standard time, as filed.
The John F. Kennedy International Airport ASOS reported 2.26 inches of rain in two hours between 4:00am and 6:00am EDT, including 1.79 inches between 5:00am and 6:00am EDT.
Park Street was closed from Suffolk Boulevard to Cayuga Avenue in Atlantic Beach due to flash flooding.
Meadow Lane was closed from Broadway to Kenridge Road in Lawrence due to flash flooding.
All lanes were closed on the Northern State Parkway at Exit 35 for Route 106/107 in Jericho.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in New York in 2015Every state in 2015This day in weather historyWarnings in New York, August 2015
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 602722, 593170, 593171, 593172.