Tropical cyclone forecast verification - measures of error
The Met Office verification scheme identifies the centre of a tropical cyclone in the model by a combination of a local maximum of relative vorticity at 850hPa and a local minimum of mean sea-level pressure.
The terms used in the statistics tables are explained below.
- Possibly verified - number of forecasts with verifying observations
- Detection rate - percentage of possibly-verified forecasts which are detected by the Met Office tropical cyclone tracker.
- Mean AT - mean of positional errors in the along track direction
- Mean CT - mean of positional errors in the cross track direction
- Track skill - percentage skill of model forecast position against CLIPER (Climatology/Persistence)
- Mean DPE - mean of direct positional errors
- Intensity tendency skill - percentage skill of model in predicting strengthening or weakening (positive if better than chance).
- Central pressure bias - mean bias in the forecast central pressure
See below for a diagrammatic explanation of track error statistics.
- DPE values are always positive
- ATE values are positive if the forecast position lies ahead of the observed position along the tropical cyclone track
- CTE values are positive if the forecast position lies right of the observed track in the northern hemisphere and left of the observed track in the southern hemisphere
- Track skill positive if the model forecast has lower errors than CLIPER
- Intensity tendency skill positive if model forecast better than chance
- Central pressure bias positive if model forecast weaker than observations
Further details of the method used to track tropical cyclones and verify forecasts in Met Office models is available in this publication:
Heming, J.T., 2016. Tropical cyclone tracking and verification techniques for Met Office numerical weather prediction models. Meteorological Applications.