Verification of model wind structure and rainfall forecasts for 2008 Atlantic storms

Tim MarchokNOAA / GFDL

Collaborators: Rob Rogers (NOAA / AOML / HRD)

Bob Tuleya (NCEP/EMC & Old Dominion Univ.)

Mark Powell (NOAA / AOML / HRD)

HFIP Hurricane Diagnostics and

Verification Workshop

NHC, Miami, FL

04 May 2009

Motivation

• Inland flooding from TC rainfall accounts for a significant percentage of deaths from U.S. landfalling TCs.

• Storm size / structure has a major impact on the amount of damage at landfall.

…both aspects have only recently begun to receive attention in terms of model evaluation

Outline

• Rainfall validation & techniques

• Application of TC QPF validation techniques to 2008 U.S. landfalling storms

• Development of model wind structure validation techniques

• Application of wind structure validation techniques to 2008 Atlantic TCs

• Rainfall patterns

• Rainfall mean & volume

• Extreme amounts

Rainfall validation: What to focus on?

The TC track: An anchor for QPF validation

GFDL

NAMGFSR-CLIPER

HWRFStage IV

Example: Hurricane Gustav 72-h total rainfall

2008 Landfalling Storms

Rainfall Patterns

20052008Equitable Threat Scores

Pattern Correlations: GFS (r = 0.78)

HWRF (r = 0.60)

GFDL (r = 0.53)

NAM (r = 0.52)

R-CLIPER (r = 0.51)

(2008)

Mean Rainfall

Rainfall volume

2008 2005

Comparison of rain volume bias by model

2008 Landfalling Storms

50% level

Difference between obs

rain value and fcst rain value at 50% level determines

index

Track-relative rain flux analyses

Rain volume: Rain flux in select bands

0–100 km

300-400 km

GFDL, HWRF GFS, NAM

Skill Indices: Pattern Matching

Pattern Matching (2005)

0.44

0.48

0.71

0.59

0 0.2 0.4 0.6 0.8 1

RCLIP

NAM

GFS

GFDL

2008 2005

• GFS performs the best in both samples

• All models have skill relative to R-CLIPER

Pattern Matching (2008)

0.40

0.48

0.78

0.52

0.50

0 0.2 0.4 0.6 0.8 1

RCLIP

NAM

GFS

HWRF

GFDL

Skill Indices: Mean / Volume

Volume (2005)

0.72

0.75

0.68

0.72

0 0.2 0.4 0.6 0.8 1

RCLIP

NAM

GFS

GFDL

2008 2005

Mean / Volume (2008)

0.36

0.80

0.79

0.32

0.70

0 0.2 0.4 0.6 0.8 1

RCLIP

NAM

GFS

HWRF

GFDL

Skill Indices: Extreme Amounts

Extreme Amounts (2005)

0.62

0.76

0.77

0.57

0 0.2 0.4 0.6 0.8 1

RCLIP

NAM

GFS

GFDL

2008 2005

• GFDL overforecasts the large amounts, HWRF underforecasts them, resulting in comparable indices

• GFS performs best despite lowest resolution

Extreme Amounts (2008)

0

0.56

0.82

0.62

0.61

0 0.2 0.4 0.6 0.8 1

RCLIP

NAM

GFS

HWRF

GFDL

Rainfall Summary

• Validation techniques address unique TC rainfall attributes:Pattern matchingRainfall volumeExtreme amounts

• TC QPF skill indices for operational forecast evaluation

• GFS most skillful in 2008 (similar to 2005)

Outline

• Rainfall validation & techniques

• Application of TC QPF validation techniques to 2008 U.S. landfalling storms

• Development of model wind structure validation techniques

• Application of wind structure validation techniques to 2008 Atlantic TCs

The importance of near-surface wind structure

Area_TSKatrina

Area_TSCharley

= Factor of 9

Focus is on continuous / homogeneous methods

• Distribution of WindsFractional areal coveragePDFs of the winds

• Radial StructureEarth-relative profilesStorm motion-relative profilesRadius of max winds

• Storm Destructive Potential IKE, SDP, WDP (Powell and Reinhold

2007)

• Others?

Cases included in study…

Distribution: Fractional Areal Coverage (34-kt winds)

Storm- sample

average at tau=00h

NW

SW SE

NE

Distribution: Fractional Areal Coverage (34-kt winds)

Storm- sample

average at tau=48h

NW

SW SE

NE

Distribution: Fractional Areal Coverage (64-kt winds)

Storm- sample

average at tau=00h

NW

SW SE

NE

Distribution: Fractional Areal Coverage (64-kt winds)

Storm- sample

average at tau=48h

NW

SW SE

NE

Radial profiles of the wind (all cases)

NW

SW SE

NE

Tau= 00h

Radial profiles of the wind (all cases)

NW

SW SE

NE

Tau= 48h

Radial profiles of the wind (Hurricanes only)

NW

SW SE

NE

Tau= 00h

Radial profiles of the wind (Hurricanes only)

NW

SW SE

NE

Tau= 48h

Radius of Maximum Winds

Forecasts of Integrated Kinetic Energy

GFDL Ike Intensity Forecasts HWRF Ike Intensity Forecasts

Max

Win

d (k

ts)

Max

Win

d (k

ts)

IKE

(T

J)

IKE

(T

J)

GFDL Ike IKE (V>18 m/s) Forecasts HWRF Ike IKE (V>18 m/s) Forecasts

Forecasts of Integrated Kinetic Energy

Wind Structure Summary

• Methods complementary to wind radii validation

• Focus on various aspects of wind fieldDistributionRadial structure IKE / Storm destructive potentialOthers…?

• Some biases already evident