Operational Tropical CycloneWind Speed Probabilities

Richard Knabb

NOAA/NWS/National Hurricane Center

2007 Interdepartmental Hurricane Conference

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– Replaced strike probabilities in 2006– Describe chances of a weather event at any

specific location– Convey chances of wind speeds of at least

particular thresholds• 34 kt (tropical storm force)• 50 kt• 64 kt (hurricane force)

– Account for combined uncertainty in official track, intensity, and size forecasts

– Extend to 5 days– Include inland locations

Overview of wind speed probabilities

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• What are the chances this wind event will happen to me at all?

• Do I need to prepare?• Cumulative period probabilities• NHC and CPHC graphics and text products• Northern hemispheric grids sent via WMO headers• National Digital Forecast Database (NDFD) CONUS grids

• When is the event most likely to start at my location?

• How much time do I have left to prepare?• Individual period probabilities• NHC and CPHC text products

What questions do these products answer?

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• What are the chances the event will be occurring at my location during a specific period?

• (example) Will hurricane-force winds occur in my city on Saturday night?

• Incremental probabilities• NDFD• Might go out via WMO headers by 2008• Being incorporated into WFO products

What questions do these products answer?

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Probabilities Convey Uncertainties in Track, Intensity, and Size Forecasts

Ernesto Advisory #11

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Magnitudes of Cumulative Probabilities Vary Greatly But Realistically

Katrina Advisory #5

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Katrina Advisory #18

Magnitudes of Cumulative Probabilities Vary Greatly But Realistically

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Changes to Graphics for 2007

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2006 Operational 120-h Graphic (64 kt)

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2007 Final 120-h Graphic (64 kt)

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2007 Preliminary 120-h Graphic (64 kt)

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Individual period probabilities help to understand timing uncertainty

Chances of tropical storm force winds in Miami

X

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Dealing With Small Probabilities

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A Challenge During Ernesto

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A Challenge During Ernesto

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A Challenge During Ernesto

Hurricane

Watch

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A Challenge During Ernesto

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– Cumulative and incremental probabilities• Updated four times daily (00, 06, 12, 18 UTC)• 6 hourly 0-120 h• 34, 50, and 64 kt

– CONUS domain only• 5 km grid spacing

– Experimental during 2006, declared operational for 2007 hurricane season

What is available via the NDFD(National Digital Forecast Database)?

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NDFD CONUS Domain

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Probabilities from NDFD Website

www.weather.gov/forecasts/graphical/sectors/conusTropicalDay.php#tabs

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Probabilities in Hurrevac

Graphics Widely Used in Emergency Management

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Going forward

• Continue outreach and education

• Compare probabilities with watches/warnings

• Account for varying forecast confidence?

• Enhance Hurrevac capabilities

• Experimental storm surge probabilities

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For Additional Information…

www.nhc.noaa.gov/aboutnhcprobs.shtml

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For Additional Information…

www.nhc.noaa.gov/archive/2005/index.shtml

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For Additional Information…

Richard.Knabb@noaa.gov