Status:Ongoing analysis Material from: Linus


1. Impact

On 29 September 2023 New York City was hit by record-breaking rainfall. Especially the eastern part of the metropolitan was hit and JFK Airport measured 219 mm/24h.

2. Description of the event

The plots below show analyses of MSLP and 6 hour rainfall from 27 September 00UTC to 1 October 00UTC, every 12th hour.

The plots below show analyses of z500 and T850 from 26 September to 2 October 00UTC, every 24 hour.

The plot below shows the total precipitation from NEXRAD for 29 September.

3. Predictability


3.1 Data assimilation


3.2 HRES

The plots below show 24-hour precipitation (29 September 00UTC - 30 September 00UTC) in observations (first plot) concatenated short forecasts (second plot) and ENS control forecasts with different lead times. The box marks 0.5x0.5 degree centred on JFK Airport. The forecasts missed the westward extent of the rainfall. note that the symobl for JFK is missing on the observation plot (should be black with 219 mm).

3.3 ENS

The plots below shows EFI and SOT for 1-day precipitation (29 September 00UTC - 30 September 00UTC)  from different initial dates.The EFI did not reach 0.9 for the area around New York even in the shortest forecast.

The plot below shows the forecast evolution plot for 24-hour precipitation (29 September 00UTC - 30 September 00UTC)  a 0.5x0.5 box  centred on JFK Airport. Mean of observations - green hourglass, Concatenated 6-hour forecasts - green dot, ENS control –red, ENS blue box-and-whisker, Model climate – cyan box-and-whisker. Ensemble mean as black diamonds. Triangle marks the maximum in the model climate based on 1800 forecasts. The area mean from NEXRAD was 160 mm.

3.4 Monthly forecasts

3.5 Comparison with other centres

4. Experience from general performance/other cases

5. Good and bad aspects of the forecasts for the event

  • Signal for the precipitation in the medium-range forecasts, but missed the westward extent and therefore missed New York

6. Additional material