Wind Speed and Intensity Probabilities

Wind Speed and Intensity Probabilities

Michael J. Brennan National Hurricane Center

2011 National Hurricane Conference Evacuation Decision Making Workshop

18 April 2011 1

Outline • The reality of forecast uncertainty • Quick overview of probability products • Why small probabilities for extreme events

matter • Reading and interpreting the probability

products • Examples

2

Atlantic 5-Year Mean NHC Forecast Errors

3

Track errors increase about 40-55 n mi per day

Intensity errors level off because intensity is much more bounded problem

All forecasts have errors

How Can You, as Decision Makers, Deal with Forecast Uncertainties?

4 NHC probability products can help

Verifying 5-day Position of Ida

TD 11 (later Hurricane Ida) Advisory Number 1

Issued 10:00 AM EST 4 November 2009

5-day position error about 600 miles

5-day NHC Forecast

Overview of Wind Speed Probability Products

5

How the Wind Speed/Intensity Probabilities are Created

6

• 1,000 realistic alternative scenarios created using – Official NHC track, intensity

and wind radii forecasts

– Historical NHC track and intensity forecast errors

– Climatology and persistence wind radii model

• Probability of exceeding 34, 50, and 64 kt wind thresholds computed

• Accounts for inland wind decay

Influence of Track Model Spread on Probabilities

• Wind speed and intensity probability products account for situational track forecast uncertainty

• Situations where track model spread is small uses smaller NHC historical track forecast errors and results in a narrower probability swath

• Situations where track model spread is large uses larger NHC historical track forecast errors and results in a broader probability swath

7

Available Probability Products 1. Wind Speed Probability

Product • Depicts location-specific

probabilities for 34-kt (tropical-storm-force), 50-kt (58-mph), and 64-kt (hurricane-force) winds

• Text product contains cumulative and individual time period onset probabilities for a fixed set of locations

• Graphics depict point-specific cumulative probabilities over a large domain 8

Available Probability Products 2. Intensity Probability Table • Shows probability of tropical cyclone intensity (maximum wind)

falling in various categories: • Dissipated, tropical depression, tropical storm, hurricane, and

Saffir-Simpson Hurricane Wind Scale categories 1-5 • Available at the top of the wind speed probability text product

and as a stand-alone graphic

9

Why do Small Probabilities of Extreme Events Matter?

10

11

U.S. Hurricane Watch and Warning Statistics (2000-2008)

• Average storm-total watch length 477 miles

• Average storm-total length with hurricane-force 89 miles winds for cases when watch issued

• Probability of hurricane winds at point under watch 19%

• Average storm-total warning length 403 miles

• Average storm-total length with hurricane-force 99 miles winds for cases when warning issued

• Probability of hurricane winds at warned point 25%

Information courtesy Andrea Schumacher CIRA

12

13

33% 22% <1% <1% <1% <1%

<1%

<1% 3%

<1% 1%

<1% 3%

<1% 2%

<1% 7%

<1%

20% <1%

<1%

1% 2%

<1% 5%

<1% 1% 1% 1%

<1% <1% <1% 8%

<1%

<1% 1% 1%

<1% 3% <1% 2%

<1% 5% <1% 1%

<1% 3%

<1% 14% <1%

<1%

<1% 3% <1% 3%

<1% 1% 1% 3% <1% 2% 1% 6%

<1%

UConn Butler UConn 1% <1%

14

Golden Beach Apalachicola

Intracoastal City

Destin Chokoloskee

Suwannee River Lake Okeechobee Tarpon Springs

Englewood

Aucilla River Fort Pierce Matagorda

San Luis Pass

St. Augustine

Pascagoula

Sabine Pass

Flamingo

Yankeetown

Vero Beach

Ann Maria Island Dry Tortugas Keaton Beach Key Largo

Port O’Connor Titusville Indian Pass

Ocean Reef

Baffin Bay

New Smyrna Bch

Card Snd Bridge

MS/AL Border

High Island

Cocoa Beach Anclote Key Craig Key

Sargent

Key West Steinhatchee R. Florida Bay Corpus Christi

Sebastian Inlet Mouth MS River

Jupiter Inlet

Ochlockonee R.

Boca Raton

Cameron

Panama City Bonita Beach Bayport

E Cape Sable Longboat Key 7-Mile Bridge

Freeport

Stuart Port Aransas Flagler Beach

St. Marks Ocean Reef Cstl

Port Mansfield Deerfield Beach

Hallandale Bch

Morgan City

Mouth Pearl R.

Grande Isle

Who is going to get hurricane force winds?

5 day forecast 14

15


Intracoastal City

Destin Chokoloskee


Englewood


San Luis Pass

St. Augustine

Pascagoula

Sabine Pass

Flamingo

Yankeetown

Vero Beach



Ocean Reef

Baffin Bay

New Smyrna Bch

Card Snd Bridge

MS/AL Border

High Island


Sargent



Jupiter Inlet

Ochlockonee R.

Boca Raton

Cameron



Freeport




Hallandale Bch

Morgan City

Mouth Pearl R.

Grande Isle

Who is going to get hurricane force winds? Golden Beach

Intracoastal City

Chokoloskee

Lake Okeechobee

Englewood

Fort Pierce

Jupiter Inlet

New Smyrna Bch

Ocean Reef

Pascagoula

Key Largo

Flamingo

Vero Beach

Titusville

Deerfield Beach

Dry Tortugas

Hallandale Bch

MS/AL Border

Cocoa Beach

Craig Key

Key West

Florida Bay

Sebastian Inlet

Card Snd Bridge

Boca Raton

Panama City

Bonita Beach

Ocean Reef Cstl

Flagler Beach

E Cape Sable

7-Mile Bridge

Stuart

4 day forecast 15

16


Intracoastal City

Destin Chokoloskee


Englewood


San Luis Pass

St. Augustine

Pascagoula

Sabine Pass

Flamingo

Yankeetown

Vero Beach



Ocean Reef

Baffin Bay

New Smyrna Bch

Card Snd Bridge

MS/AL Border

High Island


Sargent



Jupiter Inlet

Ochlockonee R.

Boca Raton

Cameron



Freeport




Hallandale Bch

Morgan City

Mouth Pearl R.

Grande Isle


Golden Beach Intracoastal City

Chokoloskee

Lake Okeechobee Lake Okeechobee

Englewood

Fort Pierce Fort Pierce

Jupiter Inlet Jupiter Inlet

New Smyrna Bch

Ocean Reef

Ocean Reef Pascagoula

Key Largo Key Largo

Flamingo

Flamingo

Vero Beach

Titusville

Deerfield Beach

Dry Tortugas

Deerfield Beach

Hallandale Bch

Hallandale Bch

MS/AL Border

Cocoa Beach

Craig Key Craig Key

Key West

Florida Bay Florida Bay

Sebastian Inlet

Card Snd Bridge Card Snd Bridge

Boca Raton

Boca Raton Panama City

Bonita Beach

Ocean Reef Cstl

Flagler Beach

E Cape Sable

7-Mile Bridge

Stuart Stuart

Ocean Reef Cstl

E Cape Sable

3 day forecast 16

17


Intracoastal City

Destin Chokoloskee


Englewood


San Luis Pass

St. Augustine

Pascagoula

Sabine Pass

Flamingo

Yankeetown

Vero Beach



Ocean Reef

Baffin Bay

New Smyrna Bch

Card Snd Bridge

MS/AL Border

High Island


Sargent



Jupiter Inlet

Ochlockonee R.

Boca Raton

Cameron



Freeport




Hallandale Bch

Morgan City

Mouth Pearl R.

Grande Isle


Golden Beach

Golden Beach Intracoastal City

Chokoloskee


Englewood



Jupiter Inlet New Smyrna Bch

Ocean Reef


Key Largo Key Largo

Key Largo

Flamingo

Flamingo

Vero Beach

Titusville

Deerfield Beach

Dry Tortugas

Deerfield Beach

Ocean Reef

Hallandale Bch

Hallandale Bch

Hallandale Bch MS/AL Border

Cocoa Beach

Craig Key Craig Key

Key West


Florida Bay Sebastian Inlet


Boca Raton


Bonita Beach

Ocean Reef Cstl

Flagler Beach

E Cape Sable

7-Mile Bridge

Stuart Stuart

Ocean Reef Cstl

Ocean Reef Cstl

E Cape Sable

E Cape Sable

2 day forecast 17

18


Intracoastal City

Destin Chokoloskee


Englewood


San Luis Pass

St. Augustine

Pascagoula

Sabine Pass

Flamingo

Yankeetown

Vero Beach



Ocean Reef

Baffin Bay

New Smyrna Bch

Card Snd Bridge

MS/AL Border

High Island


Sargent



Jupiter Inlet

Ochlockonee R.

Boca Raton

Cameron



Freeport




Hallandale Bch

Morgan City

Mouth Pearl R.

Grande Isle


Golden Beach

Golden Beach

Golden Beach

Intracoastal City

Chokoloskee


Englewood



Jupiter Inlet New Smyrna Bch

Ocean Reef


Key Largo Key Largo

Key Largo

Key Largo

Flamingo

Flamingo

Vero Beach

Titusville

Deerfield Beach

Dry Tortugas

Deerfield Beach

Ocean Reef

Hallandale Bch

Hallandale Bch

Hallandale Bch MS/AL Border

Cocoa Beach

Craig Key Craig Key

Key West


Florida Bay

Florida Bay

Sebastian Inlet


Boca Raton


Bonita Beach

Ocean Reef Cstl

Flagler Beach

E Cape Sable

7-Mile Bridge

Stuart Stuart

Ocean Reef Cstl

Ocean Reef Cstl

E Cape Sable

E Cape Sable

Ocean Reef Cstl

1 day forecast 18

What the Probabilities Tell You That the Cone of Uncertainty Can’t

19

20

20

21

Chances of hurricane-force winds at Tampa Bay and Port Charlotte

are both around 30%

Tampa

Port Charlotte

21

Impacts Can be Felt Well Outside the Cone • The cone only displays

information about track uncertainty

• It contains no information about specific impacts!

• TC impacts can occur well outside the area enclosed by the cone – TC center is expected to

move outside the cone about 1/3 of the time

– Cone narrows near the time of greatest impact due to smaller official track forecast errors

22

Impacts Can be Felt Well Outside the Cone

23

Impacts Can be Felt Well Outside the Cone

24

Interpreting the Wind Speed Probability Text Product

25

26

Wind Speed Probability Text Product

26

27

34 kt probabilities at Charlotte NC

What is the chance that winds of tropical storm force (34 kt or greater) will occur at Charlotte NC during the next five days?

Example Interpretation of Output

27

28


What is the chance that winds of tropical storm force (34 kt or greater) will occur at Charlotte NC during the next five days? 42%


28

29


What is the chance that winds of tropical storm force (34 kt or greater) will occur at Charlotte NC during the next five days? 42% When are these winds most likely to start?


29

30


What is the chance that winds of tropical storm force (34 kt or greater) will occur at Charlotte NC during the next five days? 42% When are these winds most likely to start? From 18Z Sun to 18Z Mon (18% chance)


30

Case Example Hurricane Earl (2010)

31

Hurricane Earl (2010) • An case where tropical-storm

and hurricane-force winds may or may not affect any locations along the coast of North Carolina depending on the track and size of Earl

• Given the track of Earl parallel to the coast, small changes in the forecast track result in large changes in the wind speed probabilities

• We’ll examine trends in the 34-kt and 64-kt wind speed probabilities at Cape Hatteras through the event

32

33

0 0 04

63 4 4

911

14 13 1215 16

2123

36

28

36

13

19

1 0 03

6 7

20

25

2023 23

33

46

56 55 54

62 63

69

79

90 9195

98 99 99 99 99

0

10

20

30

40

50

60

70

80

90

100

13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

Cum

ulat

ive

5-da

y Pr

obab

ility

(%)

Advisory Number

Trend of 34-kt and 64-kt Cumulative Wind Speed Probabilites at Cape Hatteras, NC for Hurricane Earl (2010)

64-kt

34-kt

Day 5 forecast point in official forecast reaches

latitude of Cape Hatteras

Hurricane Earl Advisory 16 – 5 AM EDT 29 Aug. 2010

34

34-kt probabilities 64-kt probabilities

35

0 0 04

63 4 4

911

14 13 1215 16

2123

36

28

36

13

19

1 0 03

6 7

20

25

2023 23

33

46

56 55 54

62 63

69

79

90 9195

98 99 99 99 99

0

10

20

30

40

50

60

70

80

90

100

13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

Cum

ulat

ive

5-da

y Pr

obab

ility

(%)

Advisory Number


64-kt

34-kt

Official track forecast gradually shifts westward and closest point

of approach shifts toward 72 h

Hurricane Watch Issued

Hurricane Earl Advisory 23 – 11 PM EDT 30 Aug. 2010

36


37

0 0 04

63 4 4

911

14 13 1215 16

2123

36

28

36

13

19

1 0 03

6 7

20

25

2023 23

33

46

56 55 54

62 63

69

79

90 9195

98 99 99 99 99

0

10

20

30

40

50

60

70

80

90

100

13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

Cum

ulat

ive

5-da

y Pr

obab

ility

(%)

Advisory Number


64-kt

34-kt

Continued westward shift of track and closest point of

approach now around 48 h

Hurricane Warning Issued

Hurricane Earl Advisory 28 – 5 AM EDT 1 Sep. 2010

38


39

0 0 04

63 4 4

911

14 13 1215 16

2123

36

28

36

13

19

1 0 03

6 7

20

25

2023 23

33

46

56 55 54

62 63

69

79

90 9195

98 99 99 99 99

0

10

20

30

40

50

60

70

80

90

100

13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

Cum

ulat

ive

5-da

y Pr

obab

ility

(%)

Advisory Number


64-kt

34-kt

36-h forecast point about 50 nm east of Cape Hatteras

Hurricane Earl Advisory 30 – 5 PM EDT 1 Sep. 2010

40


41

0 0 04

63 4 4

911

14 13 1215 16

2123

36

28

36

13

19

1 0 03

6 7

20

25

2023 23

33

46

56 55 54

62 63

69

79

90 9195

98 99 99 99 99

0

10

20

30

40

50

60

70

80

90

100

13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

Cum

ulat

ive

5-da

y Pr

obab

ility

(%)

Advisory Number


64-kt

34-kt

Earl begins to turn east of due north and chance of hurricane-

force winds diminishes to near 0

Hurricane Earl Advisory 35 – 11 PM EDT 2 Sep. 2010

42


Hurricane Earl – Ground Truth • Sustained tropical-storm-force were

reported at several locations on the Outer Banks

• Peak sustained wind was 60 kt at KHK Resort on Rodanthe Sound

• Several gusts to hurricane force reported

43

Timing Information About Wind Onset

44

Onset of 34-kt Winds Katrina (2005)

• Onset of 34-kt winds based on deterministic forecast issued with Advisory 16 – New Orleans, LA – 8/29 (Mon.) 08Z – Gulfport, MS – 8/29 (Mon.) 11Z

Deterministic wind field from Hurrevac valid 12Z 29 August

45

Wind Speed Probabilities Katrina (2005) Advisory 16

- - - - WIND SPEED PROBABILITIES FOR SELECTED LOCATIONS - - - - FROM FROM FROM FROM FROM FROM FROM

TIME 06Z SAT 18Z SAT 06Z SUN 18Z SUN 06Z MON 06Z TUE 06Z WED PERIODS TO TO TO TO TO TO TO 18Z SAT 06Z SUN 18Z SUN 06Z MON 06Z TUE 06Z WED 06Z THU FORECAST HOUR (12) (24) (36) (48) (72) (96) (120) NEW ORLEANS LA 34 X 1( 1) 9(10) 28(38) 34(72) 5(77) X(77) GULFPORT MS 34 X 1( 1) 8( 9) 23(32) 35(67) 5(72) 1(73)

46




Most likely period of onset of 34-kt winds at New Orleans and Gulfport is between 06Z Monday 8/29 and

06Z Tuesday 8/30 47




However, the probability that 34-kt winds will start prior to 06Z Monday 8/29 at both New Orleans and

Gulfport is nearly as large! 48

What Actually Happened? • Onset of 34-kt winds occurred between 00Z

and 06Z Monday 8/29 at New Orleans and Gulfport

– At least 3 hours earlier than shown by Hurrevac at New Orleans

– At least 5 hours earlier than shown by Hurrevac at Gulfport

49

Intensity Probability Table Examples

50

51

Hurricane Danielle Intensity Probability Table Advisory 16 – 11 AM EDT 25 Aug. 2010

• Official NHC 48-h intensity forecast: 100 MPH (Category 1)

• Verifying intensity: 135 MPH (Category 4)

51 3% chance of category 4 hurricane in 48 h verifies

Impact of Land Interaction on Intensity Probabilities

• The intensity probability table CANNOT be used to estimate the intensity of a TC at the time of landfall

• Intensity probabilities are valid at a specific TIME – not at a location – Some realizations will move faster than the official

forecast and already be inland at the time of landfall in the official forecast

– These inland realizations will be weaker and contribute to lower intensity probabilities at the forecast time period closest to landfall

• We are working with a new tool that computes the probability of landfall occurring in specific categories

52

Hurricane Ike Advisory 38 – 10 AM CDT 10 Sep 2008

53

• Official Forecast shows landfall around 72 h with forecast intensity of 120 mph (Category 3)

• Intensity probabilities shows nearly equal or higher probability of category 1 or 2 at 72 h due to some realizations being faster

• Actual landfall intensity: 110 MPH (Category 2) • Intensity at 12Z 13 September: 100 MPH (Category 2)

Summary • Wind speed probability products help you deal

with the uncertainty inherent in forecasting tropical cyclones

• Provide additional information beyond what is available in deterministic forecasts for: – Timing of event onset – Likelihood of various wind speeds occurring at your

location – Likelihood of tropical cyclone intensity

• “Low” probabilities of extreme events often warrant action!

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Documents

Wind Speed and Intensity Probabilities