Wind Speed Probabilities

A Local Perspective

Florida Governor Hurricane ConferenceMay 11-16

2014

Pablo Santos

Meteorologist In Charge

NWS Miami/South Florida Forecast Office

2014 – FLGHC

TS 22

Motivation

• What is there in it for me in this presentation?

– A better understanding of the wind speed probabilities available to you nationally and at the local level and:

• What they mean

• What questions you might have that THEY CAN answer

• How NWS can help you make better decisions using this data

• And potential advanced applications.

– Complements:• TS 23 presentation on Local Wind Forecast and its Uncertainty – Tue Morning

• TS 23 presentation on Local Application of Wind Speed Probabilities – Tue Morning

• TS 23 presentation on Local Wind Impact Recognition/Messaging – Tue Morning

• TS 24 Conveying Uncertainty to the Public – Wed Morning

D-Day Give me the Probabilities

1111

Wind Speed Probability Text Product(abbreviated)In addition to:

- Onset Probabilities: Text

- Cumulative Wind Speed Probability: Text/Graphic

11

Onset Period ProbabilitiesCumulative Probabilities

What Questions do They Answer?

• Cumulative (Available in NHC Graphic and PWSAT#; coarse time resolution) – What arethe chances that tropical storm or hurricane conditions will occur between hour 00 andXX out to 120 hours/5 days with this event at my location?

• Onset (Available in PWSAT#; coarse time resolution) – What are the chances thattropical storm or hurricane conditions will begin during a particular time period at mylocation? And given that, what is the most likely period of onset of these conditions?

• Incremental (Not available from NHC; but from NWS offices) – What are the chancesthat tropical storm or hurricane conditions will be experienced during a particularperiod at my location? How likely is the event to happen during that period? How likelyis it to last? At what values is the event becoming more plausible (likely) than justpossible?

We consider trend from advisory to advisory

Cumulative

Incremental – 12HR

Onset

Onset

Tropical

Storm

Conditions

Onset

Hurricane

Conditions

Threshold:

45%

Threshold:

35%

Threshold:

30%

Threshold:

25%

Threshold:

22.5%

Threshold:

20%

Threshold:

17.5%Incremental

Tropical

Storm

Threshold:

25%

Threshold:

20%

Threshold:

15%

Threshold:

12.5%

Threshold:

10%

Threshold:

8%

Threshold:

7%Incremental

Hurricane

What are the critical values to look for that make the event more likely than possible?

Incremental Wind Speed Probabilities

Period 2014

PWS64 PWS34

00-12 hr 25% 45%

13-24 hr 20% 35%

25-36 hr 15% 30%

37-48 hr 12.5% 25%

49-60 hr 10% 22.5%

61-72 hr 8% 20%

73-84 hr 7% 17.5%

85-96 hr 6% 15%

97-108 hr 5% 12.5%

109-120 hr 4% 10%

Local ScaleWind Speed Probabilities

Consider Trend From Advisory to

Advisory

Applications

• Communicate Risk.

• Provide objective measure of uncertainty that can be used to create new targeted products.

– Threat/Potential Impact Graphics• Briefings

• Can be used as decision making aid by planners (example follows).

• Communicate to the public graphically the threat and degree of preparation needed.

• Can be used by EM and Media along with NWS to help communicate the bottom line message to the public.

– Expressions of Uncertainty• Used to enhance forecast information during tropical cyclones (Expressions of Uncertainty).

• Can be used as decision making aid by planners.

• Trend analysis from advisory to advisory for proper risk assessment.

Cumulative: Note that

chances of hurricane-

force winds at Tampa

Bay and Port Charlotte

are both around 30%!

Tampa

Port Charlotte

IncrementalNotice: highest right

up Port Charlotte

Communicate RISK

Example: Forecast Applications: Expressions of UncertaintyAdvisory Time: 20040902_1500 (25-36 Hours – Third Period)

FRANCES (ZFP) FRANCES (Click Point)

Official in 2014

Threat/Potential Impact Graphics

Forecast Actual Threat/Potential Impact

Example: Approaching major hurricane at the onset

of the warning period (~ 36 hours).

QUESTION: When advocating the measure of protective

actions according to wind impacts, which is better?

http://www.weather.gov/tcig

Storm Intensity

Cat 3(96-113 Kt)

Threat?

OR

FORECAST VALID XX/XX00Z 31.4N 77.5W

MAX WIND XXX KT...GUSTS XXX KT.

Neal Batista

Decision Making Guide

Clearance Times

Forecast impact ≤33hrs?

FORECAST VALID XX/XX00Z 31.4N 77.5W

MAX WIND XXX KT...GUSTS XXX KT.

Available 2012 season

Neal Batista

Wind Probabilities

64KtIncremental wind

prob ≥25%?

Neal Batista

More on Trend –Wilma Example

Impact Graphics use

implicitly probabilistic

guidance. What about

their trend from

advisory to advisory

also?

• Advisory 30• Advisory 30

• Advisory 31

• Advisory 32

• Advisory 35

Take Away

• More detailed in space and time wind speed probabilities are available to and from your local NWS office:

– NWS local offices can help sort through it and target your needs with their proper application.

• Be aware of the limitations of deterministic only based information.

– And making decisions solely based on deterministic or even “alternate scenarios” only.

• Be aware of all probabilistic data available to you including

– Cumulative, Onset, Incremental

– Questions they answer

– Their temporal resolution

– Be knowledgeable of their significance and trend behavior.

– Again your local NWS office can help you sort through this

• Be aware of the potential applications of using combined deterministic/probability data and their utility in communicating the message and making decisions.

– Again, your local NWS office can help you with this

Questions…Pablo Santos

Meteorologist In ChargeNWS Miami/South Florida Forecast Office

305-220-4500pablo.santos@noaa.gov