Material from: Linus, Ervin, ...
1. Overview
Storm Amy was the first windstorm of the season for north-western Europe and hit Ireland, Scotland, Norway and other countries on 3-4 October with severe winds. The cyclone formed from the synoptic system related to the tropical cyclones Humberto and Imelda in the western Atlantic. The new low-pressure system moved quickly and intensified on 3 October and reached northern Ireland and western Scotland on that evening.
2. Analyses and Observations
2.1 Event Definition
The evaluation will focus on the 24-hour maximum mean wind on 3 October 12UTC to 4 October 12UTC in the box 1x1 degree box centred on Tiree, Scotland (56.5N, 6.9W)
2.2 Analyses
The plots below show analyses of MSLP and 6 hour rainfall from 1 October 12UTC to 4 October 12UTC, every 12th hour.
2.3 Observations
The plot below shows the time series of 10-metre wind speed observation for Tiree and analysis and first guess departures.
2.4 Climatological perspective
3. Forecasts
3.1 Data assimilation and observation usage
3.2 Single Forecasts for the event based on 00UTC forecasts (defined in Section 2.1)
Observations and analysis for the event
Control forecast (IFS 9-km resolution)
DestinE (IFS 4.4km resolution)
Hybrid
AIFS-single (AIFSv1.0 ~0.25 resolution)
AIFS-CRPS ensemble (~0.25 degree resolution)
3.3 Ensemble distribution
EFI (based on IFS 9-km ensemble)
Forecast Evolution plot
The plot below shows the evolution of 24-hour maximum mean wind in a 1x1 degree box centred on Tiree (see plots above). Note that the observation station on Tiree broke down during the event, so the observed maximum might be underestimated.
Legend:
Observation - green hourglass
Analysis - green dot
ENS CF - red dot
DestinE 4.4km - evergreen
AIFS-single - cyan dot
Hybrid - orange dot
ENS distribution - blue
AIFS-ENS distribution - pink
ENS m-climate - cyan
ENS m-climate maximum - black triangle
The plot below shows the same as above but for 24-hour maximum wind gusts. (But without AIFS.)
The plot below shows the evolution the 10-metre mean wind on 4 October 00UTC in a 0.5x0.5 degree box on the south-west coast of Norway (see observation plot to the right). The extreme wind speed in the both ensembles for the shortest forecast (step 0) is believed to be fixed by the changes in the tuning of the SPP scheme in 50r1.
The plot below shows the evolution of the minimum pressure in the box 3x3 degree box cented on 60N, 3W on 4 October 00UTC.
The plots below show the cyclone feature maps valid 4 October 00UTC with the dots coloured by the cyclone minimum pressure.
3.4 Sub-seasonal forecasts
3.5 Comparison with other centres
4. Hazard Forecasts
5. Dedicated Experiments
6. Event Summary
6.1 Good and bad aspects of the forecasts for the event
- Reasonable signal in the medium-range for a strong system
- Some really good forecasts from the Hybrid system
- Underestimation of the most extreme winds in AIFS