# Presentation: 318178

## Progress Toward Operational Implementation of Tropical Cyclone Wind Speed Probability Products

**Richard Knabb, Edward Rappaport, Michelle Mainelli, James Franklin, Chris Lauer, and Alison Krautkramer - ****National Hurricane Center**
**Scott Kiser and Tim Schott - ****NWS Headquarters**
**Mark DeMaria – ****NESDIS**** and John Knaff - ****CIRA**

**22 March 2006**

**IHC**

## Existing TPC/NHC Products Used to Convey Uncertainty

**Watch/****Warning Graphic****Indicates forecast track and long-term mean error**

## Existing TPC/NHC Products Used to Convey Uncertainty

**Existing TPC/NHC Products Used to Convey Uncertainty**

**Strike Probability Graphic****Indicates chances of a “close approach” of the center**

## Existing TPC/NHC Products Used to Convey Uncertainty

**Existing TPC/NHC Products Used to Convey Uncertainty**

**Strike Probability Text Product**

## 	Need for improved means of conveying tropical cyclone forecast uncertainty to various types of users

New product is about a weather event at any specific location
Conveys chances of wind speeds of at least particular thresholds
34 kt (tropical storm force)
50 kt
64 kt (hurricane force)
Accounts for combined uncertainty in track, intensity, and size
Extends to 5 days
Includes inland locations
Will replace strike probabilities in 2006

- New product is about a *weather event* at any specific location
- Conveys chances of wind speeds of at least particular thresholds
- 34 kt (tropical storm force)
- 50 kt
- 64 kt (hurricane force)
- Accounts for combined uncertainty in track, intensity, and size
- Extends to 5 days
- Includes inland locations
- Will replace strike probabilities in 2006

**Why a new probability product?**

## Text product (one per storm)
Atlantic (NHC)
Eastern Pacific (NHC)
Central Pacific (CPHC)

Website graphics (basin-wide and storm-centered)
Atlantic (NHC)
Eastern Pacific (NHC)
Central Pacific (CPHC)
Western Pacific (CPHC)

- Atlantic (NHC)
- Eastern Pacific (NHC)
- Central Pacific (CPHC)
- Website graphics (basin-wide and storm-centered)
- Atlantic (NHC)
- Eastern Pacific (NHC)
- Central Pacific (CPHC)
- Western Pacific (CPHC)

**What are the new wind speed probability products?**

## 	Answers to three main questions:

What are the chances this event is going to happen to me?
Do I need to prepare?
Cumulative period probabilities
New graphics and text products from NHC and CPHC

When is the event most likely to start at my location?
How much time do I have left to prepare?
Individual period probabilities
New text products from NHC and CPHC

What are the chances this event will be happening to me on a particular day (or part of a day)?
How long will the storm last?  Will the weather be bad on Saturday?
Incremental probabilities
Potential future products from local NWS Forecast Offices

**What are the chances this event is going to happen to me?**
*Do I need to prepare?*
**Cumulative** period probabilities
- New graphics and text products from NHC and CPHC
**When is the event most likely to start at my location?**
*How much time do I have left to prepare?*
**Individual **period probabilities
- New text products from NHC and CPHC
**What are the chances this event will be happening to me on a particular day (or part of a day)?**
*How long will the storm last?  Will the weather be bad on Saturday?*
**Incremental** probabilities
- Potential **future** products from local NWS Forecast Offices

**What do the new probability products tell you?**

**NHC Website Probability Graphics**

**34 kt example**

**NHC Website Probability Graphics**

**34 kt example**

**NHC Website Probability Graphics**

**50 kt example**

**NHC Website Probability Graphics**

**50 kt example**

**NHC Website Probability Graphics**

**64 kt example**

**NHC Website Probability Graphics**

**64 kt example**

**Wind Speed Probability Text Product****(abbreviated)**

## Example Interpretation of Output

**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**

## Example Interpretation of Output

**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?**
**	****42%**

**Example Interpretation of Output**

## Example Interpretation of Output

**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?**
**	****42%**
**When are these winds most likely to start?**

**Example Interpretation of Output**

## Example Interpretation of Output

**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?**
**	****42%**
**When are these winds most likely to start?**
**	****From 18Z Sun to 18Z Mon (18% chance)**

**Example Interpretation of Output**

## Slide 20

## Exact track forecast goes over Galveston, but there is also a significant chance of hurricane force winds farther east where actual landfall occurred.

**Exact track forecast goes over Galveston, but there is also a significant chance of hurricane force winds farther east where actual landfall occurred.**

## Slide 22

## Challenges and Ongoing Work

- Significant training and outreach needed
- Lessen the focus on exact track forecast
- Do users understand probabilities?
- “Small” probabilities
- Enhancements to graphical products
- Faster creation of grids and graphics created from them
- Potential use by NWS forecast offices in their products
- Verification
- Objective guidance for watch/warning breakpoints
- Gridded products for NDFD

## Supplemental Slides

## Who Would Use Wind Speed Probabilities?

| Primary Users | Application |
| --- | --- |
| Emergency managers, professional decision makers | Risk assessment; decision making |
| Department of Defense | Risk assessment; decision making |
| TPC/NHC, CPHC, JTWC, and int’l offices with TC warning responsibility | Watch/warning calibration; supplement to deterministic data; communication of risk |
| NWS Forecast Offices | Enhanced text or graphical products |

| Desired Users | Application |
| --- | --- |
| Media | Communication of risk |
| Public | Risk assessment and/or decision making by knowledgeable users |

## Create large set of plausible tracks and intensities (ensemble members) roughly centered around the current official forecast

Determined by random sampling of historical track and intensity errors in official forecasts (since 2001)

Intensities consider whether a particular ensemble member is over land or water

- Determined by random sampling of historical track and intensity errors in official forecasts (since 2001)
- Intensities consider whether a particular ensemble member is over land or water

**Wind Speed Probability Methodology**

## The size of the tropical cyclone (set of wind radii) for each ensemble member is determined by a climatology and persistence (CLIPER) model and its error components
CLIPER models provide:
A baseline forecast for evaluating the skill of other models and forecasts
Basic guidance to use in making forecast for current storm
A general idea of how difficult a forecast was (based on CLIPER errors)
Wind radii CLIPER combines:
Recent trends and persistence in initial wind radii of the current storm
Climatological radii (based on operational estimates in several past storms) that vary with the storm’s initial and forecast location, forward speed, and intensity.  In general:
Storms get larger in middle latitudes
Stronger storms have larger wind radii
Faster storms have larger wind radii to the right of direction of motion
For wind radii CLIPER, persistence dominates through about 36 h of the forecast, then climatology dominates

- CLIPER models provide:
- A baseline forecast for evaluating the skill of other models and forecasts
- Basic guidance to use in making forecast for current storm
- A general idea of how difficult a forecast was (based on CLIPER errors)
- Wind radii CLIPER combines:
- Recent trends and persistence in initial wind radii of the current storm
- Climatological radii (based on operational estimates in several past storms) that vary with the storm’s initial and forecast location, forward speed, and intensity.  In general:
**Storms get larger in middle latitudes**
**Stronger storms have larger wind radii**
**Faster storms have larger wind radii to the right of direction of motion**
- For wind radii CLIPER, persistence dominates through about 36 h of the forecast, then climatology dominates

**Wind Speed Probability Methodology**

## Operational wind radii definition:
Maximum extent of a particular wind speed somewhere in a quadrant of the storm
Creating wind swaths from these radii can overestimate area affected by that wind speed

For wind speed probabilities, adjustment is made so that the wind radii represent the average (not maximum) extent of winds in each quadrant

This adjustment makes wind speed probabilities more realistic for describing what might actually happen at any location

*Maximum* extent of a particular wind speed somewhere in a quadrant of the storm
- Creating wind swaths from these radii can overestimate area affected by that wind speed
- For wind speed probabilities, adjustment is made so that the wind radii represent the *average* (not maximum) extent of winds in each quadrant
- This adjustment makes wind speed probabilities more realistic for describing what might actually happen at any location

**Wind Speed Probability Methodology**

## Swaths of particular wind speeds are then computed for each ensemble member.

Probabilities are computed on a lat-lon grid (0.5 degree) by counting the fraction of ensemble members in which each grid point falls within a swath of each wind speed.

- Probabilities are computed on a lat-lon grid (0.5 degree) by counting the fraction of ensemble members in which each grid point falls within a swath of each wind speed.

**Wind Speed Probability Methodology**

## Computed and output on a single Northern Hemispheric grid
Done after each forecast cycle for all active tropical cyclones in the following basins:
Atlantic (includes Caribbean and Gulf of Mexico)
Eastern Pacific
Central Pacific
Western Pacific
Can be converted to graphics and text

- Done after each forecast cycle for all active tropical cyclones in the following basins:
- Atlantic (includes Caribbean and Gulf of Mexico)
- Eastern Pacific
- Central Pacific
- Western Pacific
- Can be converted to graphics and text

**Example of 0-120 hour cumulative probabilities of 34 kt winds**

**Wind Speed Probability Methodology**

## 34-KT WIND RADII FORECAST VERIFICATION: “DRCL” IS A CLIPER MODEL

**34-KT WIND RADII FORECAST VERIFICATION: “DRCL” IS A CLIPER MODEL**

## 64 kt Cumulative

- 0-120 h

- 18 UTC Thu 12 Aug

- Hurricane Charley (2004)

- Note that chances of hurricane conditions at Tampa Bay and Port Charlotte are both around 30%!