Modeling Tropical Cyclone Modeling Tropical Cyclone Gridded Wind Field Gridded Wind Field

Forecasts Forecasts

26th Conference on Hurricanes and Tropical 26th Conference on Hurricanes and Tropical MeteorologyMeteorology

3—7 May 20043—7 May 2004Miami, FLMiami, FL

Ken WatersKen Waters

Joel ClineJoel Cline

National Weather ServiceNational Weather Service

Honolulu, HawaiiHonolulu, Hawaii

Modeling Tropical Cyclone Gridded Modeling Tropical Cyclone Gridded Wind Field ForecastsWind Field Forecasts

• BackgroundBackground

• Process/AlgorithmProcess/Algorithm

• IssuesIssues

• ResultsResults

• Future PlansFuture Plans

Background: PurposeBackground: Purpose• The goal:The goal:

– An hourly forecast estimate of surface wind speeds and An hourly forecast estimate of surface wind speeds and direction for 31 island points in the West Pacificdirection for 31 island points in the West Pacific

• Needed for:Needed for:

– Terminal Aviation Forecasts (TAFs) for 24-hour periodTerminal Aviation Forecasts (TAFs) for 24-hour period– Hourly wind forecast needed to help determine start/stop Hourly wind forecast needed to help determine start/stop

times for Tropical Storm and Typhoon Watches and times for Tropical Storm and Typhoon Watches and WarningsWarnings

– Wind grid information for possible initialization of digital Wind grid information for possible initialization of digital wind grids (National Digital Forecast Database) wind grids (National Digital Forecast Database)

Background: Warning PointsBackground: Warning Points

• Official Tropical Cyclone Warnings Official Tropical Cyclone Warnings are produced by the DoD Joint are produced by the DoD Joint Typhoon Warning Center in Pearl Typhoon Warning Center in Pearl HarborHarbor

• Forecast of position and maximum Forecast of position and maximum sustained wind speed for Hours 00, sustained wind speed for Hours 00, 12, 24, 36, 48, 72, 96, and 12012, 24, 36, 48, 72, 96, and 120

• Estimated wind radii by quadrant for Estimated wind radii by quadrant for Hours 00-72Hours 00-72

Background: Source WarningsBackground: Source Warnings

Background: JTWC forecastBackground: JTWC forecast

Max Wind

12 Hour ForecastLat/LongMax Wind

Initial PositionLat/Long

24 Hour Forecast

Background: JTWC forecast – Background: JTWC forecast – Example Graphic Showing Example Graphic Showing

Wind Radii InformationWind Radii Information

Process/Algorithm: Rankine Process/Algorithm: Rankine VortexVortex

• Anthes (1982):Anthes (1982):

000

0 rrRwherer

RRVrV

x

V(r) = Velocity at distance “r” from center of storm

V(R0) = Maximum Wind Speed at Radius of Maximum Wind, R0

x = exponential “form factor”, typically between 0.5 and 0.7

r0 = Radius of storm influence

Process/Algorithm: Rankine Process/Algorithm: Rankine VortexVortex

• For winds inside the Radius of For winds inside the Radius of Maximum Wind (RMW), use:Maximum Wind (RMW), use:

influence of radius maximum r

WindMaximum of Radius R

storm ofcenter from distance radial r

0

0

000

0

rRrwhere

R

rRVrV

Process/Algorithm:Process/Algorithm:

• Interpolate storm forecast to obtain hourly Interpolate storm forecast to obtain hourly positions and maximum wind speedpositions and maximum wind speed

• Apply the wind formula for a regular grid Apply the wind formula for a regular grid centered upon the storm at each hourly centered upon the storm at each hourly position as well as for selected point position as well as for selected point locations (e.g., islands) at each hour based locations (e.g., islands) at each hour based on distance from storm to the islandon distance from storm to the island

• Compute simple wind direction orthogonal Compute simple wind direction orthogonal to line between the storm and the pointto line between the storm and the point

Process/Algorithm:Process/Algorithm:

• National Digital Forecast Database requires National Digital Forecast Database requires offices to produce surface wind grids of at offices to produce surface wind grids of at least 5 km resolution every 3 hoursleast 5 km resolution every 3 hours

• Following example shows a method of Following example shows a method of populating the wind field based solely on the populating the wind field based solely on the wind radii (quadrant) information inside the wind radii (quadrant) information inside the warning --- not using Rankine vortexwarning --- not using Rankine vortex

Issues:Issues:• Determination of Radius of Maximum Wind (RMW) Determination of Radius of Maximum Wind (RMW)

--- not part of forecast but input to the formula--- not part of forecast but input to the formula

• Determination of the exponential “shape” factor Determination of the exponential “shape” factor • How rapidly does wind speed fall off as one moves away from How rapidly does wind speed fall off as one moves away from

center?center?

• Variances include spectrum from huge storm down to “midget” Variances include spectrum from huge storm down to “midget” typhoonstyphoons

• Inherent dangers with using a highly deterministic Inherent dangers with using a highly deterministic approach to describe difficult-to-predict tropical approach to describe difficult-to-predict tropical cyclone movement and intensitycyclone movement and intensity

Results: Typhoon Sudal Apr 9, Results: Typhoon Sudal Apr 9, 20042004

Warning #20Warning #20SYMMETRIC MODEL PREDICTED WINDS FOR:

Koror Ngulu Yap

0 340 25 334 56 59 69

1 339 26 330 59 66 73

2 338 26 325 62 74 77

3 337 27 319 66 84 81

4 336 27 312 69 95 84

5 335 28 304 72 106 84

6 334 28 296 74 118 83

7 333 29 286 76 128 80

8 332 29 277 76 136 76

9 330 30 267 75 144 72

10 329 31 259 73 150 68

11 327 31 251 70 154 64

12 326 32 245 67 158 61

13 324 32 241 63 164 59

14 321 33 238 59 169 56

15 319 33 236 56 173 54

16 316 33 234 53 176 52

17 314 34 232 50 180 50

18 311 34 231 48 182 48

HOURLY POSITION/CLOSEST POINT:

# Lat Lon Wind Mvmt Dstnc/Dirctn

from (naut mi)

0 8.8 138.5 110.0 282 8 55 SSE Yap

1 8.8 138.4 110.4 282 8 50 SSE Yap

2 8.9 138.3 110.8 282 8 45 SSE Yap

3 8.9 138.2 111.2 282 8 42 S Yap

4 8.9 138.0 111.7 282 8 40 S Yap

5 8.9 137.9 112.1 282 8 40 SSW Yap

6 8.9 137.8 112.5 282 8 42 SSW Yap

7 9.0 137.7 112.9 282 8 44 SW Yap

8 9.0 137.6 113.3 282 8 48 SW Yap

9 9.0 137.4 113.8 282 8 50 N Ngulu

10 9.1 137.3 114.2 282 8 53 N Ngulu

Future PlansFuture Plans

• Asymmetric wind structure (moving storm)Asymmetric wind structure (moving storm)

• Environmental blending (e.g., SW monsoon Environmental blending (e.g., SW monsoon flow)flow)

• Verification (using…? QuikSCAT? Recon?)Verification (using…? QuikSCAT? Recon?)

• Create netCDF grids for possible use in Create netCDF grids for possible use in initializing National Digital Forecast initializing National Digital Forecast Database wind gridsDatabase wind grids

• Explore methods to estimate exponential Explore methods to estimate exponential factor and Radius of Maximum Windfactor and Radius of Maximum Wind

Questions?Questions?

• Text data files can be found at:Text data files can be found at:– http://www.prh.noaa.gov/hq/regsci/windhttp://www.prh.noaa.gov/hq/regsci/wind– Graphics planned for this spring/summerGraphics planned for this spring/summer

Ken WatersRegional Scientist

National Weather Service, Pacific Region737 Bishop St., Ste. 2200

Honolulu, HI

808-532-6413, cell: 808-271-7204Ken.waters@noaa.gov