Status: Ongoing analysis Material from: Linus
1. Impact
On 29 August the tropical cyclone made landfall on the shores of Louisiana as a Cat 4 hurricane. The weather system continued to the north-east, and caused severe flash floods in New York City on 1-2 September. The events were discussed in the WMO/WWRP Hiweather project for evaluation of the warning chain.
2. Description of the event
The plots below show analyses of MSLP and 6-hour forecasts of precipitation from 29 August 12UTC to 3 September 00UTC, every 12 hour.
3. Predictability
3.1 Data assimilation
3.2 HRES
The plots below show observations from SYNOP (first plot) and HRES forecasts of 24-hour precipitation valid 1 September 12UTC - 2 September 12UTC, from different initial dates (all 00UTC).
3.3 ENS
The plots below show the tropical cyclone track for the operational ECMWF forecasts from 29 August 00UTC (first plot) to 24 August 00UTC (last plot). The symbols shows the position on 29 August 18UTC. HRES (red), ENS CF (blue), ENS PF (grey) and BestTrack (black).
The plots below show the tropical cyclone track for the e-suite ECMWF forecasts from 29 August 00UTC (first plot) to 24 August 00UTC (last plot). The symbols shows the position on 29 August 18UTC. HRES (red), ENS CF (blue), ENS PF (grey) and BestTrack (black).
The plots below show EFI for 1-day precipitation 2 September, from different initial times. Note that the rain in New York City fell between 1 and 2 September, but the EFI is only calculated for 00-00UTC.
The plot below shows the forecast evolution plot for 24-hour precipitation valid 1 Sept 12UTC - 2 Sept 12UTC over New York City. HRES –red, ENS CF – purple, ENS blue box-and-whisker, Model climate – red box-and-whisker. Triangle marks the maximum in the model climate based on 1200 forecasts and the green hourglass marks the average of the observations in the 0.5 degree box.
3.4 Monthly forecasts
3.5 Comparison with other centres
The plots below show the tropical cyclone track for the operational ECMWF forecasts from 27 August 00UTC for ECMWF operational, ECMWF e-suite, GEFS and MOGREPS ensembles. The symbols shows the position on 29 August 18UTC. HRES (red), ENS CF (blue), ENS PF (grey) and BestTrack (black). The is based on tracks from the TIGGE XML exchange.
4. Experience from general performance/other cases
5. Good and bad aspects of the forecasts for the event
- The signal of the system passing New York City was picked up from 28 August and onwards
- Also short-range HRES forecasts predicted the most intense rainfall too far north, in relation to New York City