# Presentation: 668481

## Prediction of Consensus TC Track Forecast Error and

**Correctors to Improve Consensus TC Track Forecasts**
**Joint Hurricane Testbed Project**
**James S. Goerss**
**NRL  Monterey **
**March 22, 2006**

## Predicting TC Track Forecast Error

** ****	****Predictors of consensus forecast error must be ****	****quantities that are available prior to the time when ****	****official forecasts must be issued.**
**	****Consensus model spread is defined to be the average ****	****distance of the member forecasts from the consensus ****	****forecast.**
** ****	****The possible predictors are consensus model spread; ****	****initial and forecast TC intensity; initial TC location and ****	****forecast displacement of TC location (latitude and ****	****longitude); TC speed of motion; and number of ****	****members available (for CONU).**

## Predicting TC Track Forecast Error

** ****	****Using stepwise linear regression and the ****	****aforementioned pool of predictors for the 2001-2004 ****	****seasons, regression models were found to predict ****	****consensus TC track forecast error for each combination ****	****of forecast length, consensus model, and basin.**
** ****	****The regression models were then used to determine the ****	****radii of circular areas drawn around the consensus ****	****model forecast positions within which the verifying TC ****	****position was expected to be contained approximately ****	****75% of the time.**
**	****These circular areas were graphically displayed on the ****	****ATCF for use by the forecasters at NHC and JTWC. ****	**

## 2005 Atlantic 

**2005 Atlantic **
**Forecast Availability Percentage**

## 72-h Predicted Consensus Error 

**72-h Predicted Consensus Error **
**Hurricane Katrina - 12Z 26 August 2005**

## 72-h Predicted Consensus Error 

**72-h Predicted Consensus Error **
**Hurricane Katrina - 18Z 26 August 2005**

## 72-h Predicted Consensus Error 

**72-h Predicted Consensus Error **
**Hurricane Rita - 06Z 21 September 2005**

## 48-h Predicted Consensus Error 

**48-h Predicted Consensus Error **
**Hurricane Rita - 06Z 22 September 2005**

## 2005 Atlantic and Eastern North Pacific

**2005 Atlantic and Eastern North Pacific**
** ****Predicted Error Validation for CONU**

## Predicting Consensus Model Correctors

** ****	****The techniques used to predict consensus error were ****	****applied to predict the east-west and north-south ****	****forecast error of the consensus models.**
**	****Regression models to predict CONU and GUNA east-****	****west and north-south forecast error for all forecast ****	****lengths in the Atlantic were derived using the ****	****aforementioned pool of predictors for the 2001-2002, ****	****2001-2003, and 2001-2004 seasons.**
** ****	****These predicted errors were then used as correctors to ****	****be applied to the consensus model forecasts for the ****	****2003, 2004, and 2005 seasons, respectively.**

## Predicting Consensus Model Correctors

** ****	****The mean of the CONU and GUNA east-west and north-****	****south forecast errors for all forecast lengths in the ****	****Atlantic were also found for the 2001-2002, 2001-2003, ****	****and 2001-2004 seasons to be used as bias correctors ****	****for the consensus models for the 2003, 2004, and 2005 ****	****seasons, respectively.**
**	****For both CONU and GUNA, the bias correctors were ****	****found to be more effective than the statistical correctors ****	****derived using the regression models for forecast ****	****lengths less than or equal to 72 h.**
** ****	****For CONU, the application of only the statistical ****	****corrector for the north-south error was most effective at ****	****96 h and 120 h.  For GUNA, the application of the north-****	****south statistical corrector and the east-west bias ****	****corrector was most effective at 96 h and 120 h.**

## 2003-2005 Atlantic TC Forecast Error (nm)

**Statistical Correction - Homogeneous Comparison**

**1075**

**716**

**456**

**Number of Forecasts**

**873**

**572**

## 2003-2005 Atlantic TC Forecast Error (nm)

**Statistical Correction - Homogeneous Comparison**

## CONU and CCON Forecast Tracks

**CONU and CCON Forecast Tracks**
**Hurricane Wilma – 12Z 20 October 2005**

## Summary

**	****For the 2005 Atlantic season, the circular areas displayed by ****	****the CONU Predicted Consensus Error product contained ****	****the verifying TC position 76%, 77%, 77%, 75%, and 75% of ****	****the time at 24 h, 48 h, 72 h, 96 h, and 120 h, respectively.  **
** ****	****For the 2005 Atlantic season, the predicted radii for CONU ****	****varied from 30-200 nm at 24 h, 55-285 nm at 48 h, 60-370 nm ****	****at 72 h, 135-590 nm at 96 h, and 180-840 nm at 120 h. (NHC ****	****Potential Day 1-5 Track Area graphic uses 81, 150, 225, 282, ****	****and 374 nm, respectively) **
** ****	****For the 2005 eastern North Pacific season, the circular ****	****areas displayed by the CONU Predicted Consensus Error ****	****product contained the verifying TC position 76%, 84%, 83%, ****	****90%, and 94% of the time at 24 h, 48 h, 72 h, 96 h, and 120 h, ****	****respectively.  This was consistent with the exceptionally ****	****small CONU forecast errors of 80 nm at 48 h, 111 nm at 72 h, ****	****136 nm at 96 h, and 161 nm at 120**** h. **

## Summary

**	****For the 2005 eastern North Pacific season, the predicted ****	****radii for CONU varied from 55-160 nm at 24 h, 110-205 ****	****nm at 48 h, 135-370 nm at 72 h, 175-450 nm at 96 h, and 255-****	****535 nm at 120 h.  (NHC Potential Day 1-5 Track Area graphic ****	****uses 72, 131, 185, 196, and 223 nm, respectively). **
** ****	****Corrected consensus forecasts (CCON and CGUN) were ****	****derived for the 2003-2005 seasons using a combination of ****	****bias and regression-based statistical correctors.  The CCON ****	****improvements were significant at the 99% level at 24-72 h, ****	****the 90% level at 96 h, and the 97% level at 120 h.  The CGUN ****	****improvements were significant at the 99% level at 24-72 h, ****	****the 80% level at 96 h, and the 85% level at 120 h.****	**

## Questions?

## 2005 Atlantic TC Forecast Error (nm)

**2005 Atlantic TC Forecast Error (nm)**
**Statistical Correction from 2001-2004 Data**
**Homogeneous Comparison**

**448**

**290**

**167**

**Number of Forecasts**

**358**

**225**

## 2005 Atlantic TC Forecast Error (nm)

**2005 Atlantic TC Forecast Error (nm)**
**Statistical Correction from 2001-2004 Data**
**Homogeneous Comparison**

**386**

**216**

**90**

**Number of Forecasts**

**297**

**154**

## 2004 Atlantic TC Forecast Error (nm)

**2004 Atlantic TC Forecast Error (nm)**
**Statistical Correction from 2001-2003 Data**
**Homogeneous Comparison**

**338**

**249**

**174**

**Number of Forecasts**

**289**

**210**

## 2004 Atlantic TC Forecast Error (nm)

**2004 Atlantic TC Forecast Error (nm)**
**Statistical Correction from 2001-2003 Data**
**Homogeneous Comparison**

**299**

**216**

**132**

**Number of Forecasts**

**253**

**165**

## 2003 Atlantic TC Forecast Error (nm)

**2003 Atlantic TC Forecast Error (nm)**
**Statistical Correction from 2001-2002 Data**
**Homogeneous Comparison**

**289**

**177**

**115**

**Number of Forecasts**

**226**

**137**

## 2003 Atlantic TC Forecast Error (nm)

**2003 Atlantic TC Forecast Error (nm)**
**Statistical Correction from 2001-2002 Data**
**Homogeneous Comparison**

**236**

**145**

**92**

**Number of Forecasts**

**181**

**112**