# Presentation: 004601

## 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 7, 2007**

## 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 2001-2005 ****	****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. ****	****This graphical predicted consensus error product is ****	****referred to as GPCE (“gypsy”).**

## 2006 Atlantic

**2006 Atlantic**
**Consensus (Ensemble) Model Comparison**

**215**

**179**

**143**

**107**

**83**

**Number of Forecasts**

**Forecast Availability Percentage**

**TC Forecast Error (nm)**

## 48-h Predicted Consensus Error 

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

## GPCE Validation

**GPCE Validation**
**2005-2006 Atlantic and Eastern North Pacific **

**GPCE Validation**
** ****(Percent)**

**CONU Forecast Error**
** ****(nm)**

## Predicting Consensus Model Correctors

**Atlantic**

** ****	****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 2001-2005 ****	****seasons.**
** ****	****The means of the CONU and GUNA east-west and ****	****north-south forecast errors for all forecast lengths in ****	****the Atlantic were also found for the 2001-2005 seasons ****	****to be used as bias correctors.**

## Predicting Consensus Model Correctors

**Atlantic**

** ****	****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.**
** ****	****Using these strategies, “corrected consensus” forecast ****	****guidance (CCON and CGUN) was produced for the ****	****2006 season and installed on the ATCF as experimental ****	****guidance.**

## 2006 Atlantic TC Forecast Error (nm)

**2006 Atlantic TC Forecast Error (nm)**
**Corrected Consensus - Homogeneous Comparison**

**207**

**131**

**75**

**Number of Forecasts**

**169**

**97**

## 2006 Atlantic TC Forecast Error (nm)

**2006 Atlantic TC Forecast Error (nm)**
**Corrected Consensus - Homogeneous Comparison**

**173**

**98**

**50**

**Number of Forecasts**

**136**

**68**

## Predicting Consensus Model Correctors

**Eastern North Pacific**

**	****Regression models to predict CONU east-west and ****	****north-south forecast error for all forecast lengths in the ****	****eastern North Pacific were derived using the ****	****aforementioned pool of predictors for the 2002-2005 ****	****seasons.**
** ****	****The means of the CONU east-west and north-south ****	****forecast errors for all forecast lengths in the eastern ****	****North Pacific were also found for the 2002-2005 ****	****seasons to be used as bias correctors.**
** ****	****The statistical correctors derived using the regression ****	****models were found to be more effective than the bias ****	****correctors for all forecast lengths and were used to ****	****produce “corrected consensus” guidance (CCON) for ****	****the 2006 season.**

## 2002-2006 Eastern North Pacific 

**120-h CONU East-West Error vs. Initial Latitude**

## CONU and CCON Forecast Tracks

**CONU and CCON Forecast Tracks**
**Hurricane Daniel – 00Z 20 July 2006**

## 2006 Eastern North Pacific TC Forecast Error (nm)

**2006 Eastern North Pacific TC Forecast Error (nm)**
**Corrected Consensus - Homogeneous Comparison**

**297**

**156**

**61**

**Number of Forecasts**

**223**

**98**

## Summary

**	****For the 2006 Atlantic season, the circular areas displayed by ****	****GPCE contained the verifying TC position 81%, 79%, 74%, ****	****79%, and 77% of the time at 24 h, 48 h, 72 h, 96 h, and 120 h, ****	****respectively.  **
** ****	****For the 2006 Atlantic season, the predicted radii for CONU ****	****varied from 40-105 nm at 24 h, 70-240 nm at 48 h, 115-400 ****	****nm at 72 h, 165-560 nm at 96 h, and 200-550 nm at 120 h. ****	****(NHC Potential Day 1-5 Track Area graphic uses 70, 128, ****	****188, 231, and 303 nm, respectively) **
** ****	****For the 2006 eastern North Pacific season, the circular ****	****areas displayed by GPCE contained the verifying TC ****	****position 61%, 67%, 63%, 68%, and 67% of the time at 24 h, ****	****48 h, 72 h, 96 h, and 120 h, respectively.  **

## Summary

**	****For the 2005 eastern North Pacific season, the predicted ****	****radii for CONU varied from 25-105 nm at 24 h, 70-180 ****	****nm at ****	****48 h, 100-325 nm at 72 h, 145-340 nm at 96 h, and 200-535 ****	****nm at 120 h.  (NHC Potential Day 1-5 Track Area graphic ****	****uses 66, 117, 167, 192, and 231 nm, respectively). **
** ****	****Corrected consensus forecast guidance (CCON and CGUN) ****	****was produced for the Atlantic and installed on the ATCF as ****	****experimental guidance for the 2006 season.  For most ****	****forecast lengths the CCON and CGUN forecast errors were ****	****slightly less than those for CONU and GUNA.**
**	****Corrected consensus forecast guidance (CCON) was ****	****produced for the eastern North Pacific and will be installed ****	****on the ATCF for use as experimental guidance for the 2007 ****	****season.  Independent test results for 2006 were quite ****	****promising.**

## Questions?