The terms used in the statistics tables are explained below.
- Possibly verified - number of forecasts fulfilling requirements 1, 2 and 4 below
- Detection rate - percentage of possibly-verified forecasts which also fulfil requirement 3 below
- Mean DX - mean of positional errors in the east-west direction
- Mean DY - mean of positional errors in the north-south direction
- 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
- Mean DPE - mean of direct positional errors
- Intensity skill - percentage skill of model in predicting strengthening or weakening (positive if better than chance).
All errors are measured in kilometres except where indicated.
- Observed maximum wind at least 31 knots at the verifying time.
- Forecast tropical cyclone centre equatorwards of 50 degrees.
- Forecast tropical cyclone centre relative vorticity above a critical limit for verification (1.30x10-4 per second).
- Observation within 6 hours of verifying time present for use in verification.
- Track skill is defined as:- (CLIPER DPE - Model DPE) / CLIPER DPE x 100%
- Positive skill indicates the model forecast is better than CLIPER
- Negative skill indicates the CLIPER forecast is better than the model
See below for a diagrammatic explanation of other error statistics and their sign conventions, for full details see the forecast tracks verification method.
Key to terms
|Forecast position: verifying against observation OB2|
|Direct positional error|
|Error in the east-west direction|
|Error in the north-south direction|
|Error in the along-track direction|
|Error in the cross track direction|
- DPE values are always positive
- DX errors are positive if the forecast position lies eastwards of the observed position
- DY errors are positive if the forecast position lies polewards of the observed position
- AT errors are positive if the forecast position lies ahead of the observed position along the tropical cyclone track
- CT errors 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.
Last Updated: 24 August 2011