The Local Wind Forecast and Its Uncertainty (Completing the Wind Forecast)

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1 The Local Wind Forecast and Its Uncertainty (Completing the Wind Forecast) Florida Governor Hurricane Conference May Pablo Santos Meteorologist In Charge NWS Miami/South Florida Forecast Office 2014 FLGHC TS 23

2 Motivation What is there in it for me in this presentation? A better appreciation of the approach used by local offices to downscale NHC s forecast to provide you more detailed locally driven information. A better understanding of the limitations behind deterministic only based information and basing decisions on those alone. 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.

3 NHC Wind Forecasts NHC Official Forecast Full Radii Only Out to 36 Hrs 50/34 kts Radii Only Out to 72 Hrs No Radii Days 96/120 Hrs

4 WFO Wind Grid Forecasts

5 WFO Wind Grid Forecasts

6 NHC/WFO Wind Forecasts So when making forecast of Wind locally using NHC guidance, NWS offices then have to refine that forecast to create a wind grid based on: Conceptual models Climatology-based data Local knowledge Understanding of smaller scale processes Diagnostic data for present conditions Other tools such as high resolution models, when available

7 NHC/WFO Wind Forecasts Limitations Intensity changes are depicted as a steady trend in space and time. Wind Speeds can be artificially reduced prior to landfall as they are interpolated within 12-hour forecast points. They are worse in days 4 and 5. We are required to make wind grids forecasts at the hourly scale out to 48 hours, 3 hourly out to 72 hours, and 6 hourly out to 120 hours with this guidance on a 2.5 km grid. The limitations (which translate into errors) of the assumptions listed so far are magnified the higher the resolution of the wind grids. This is how the local offices create a local wind forecast from the NHC forecasts. ASSUMPTIONS AND LIMITATIONS RESULT IN GREATLY MAGNIFIED ERRORS when looking at deterministic wind forecasts alone. HURRIVAC has the same limitations.

8 Local Wind Forecast What is the Point? Approach currently used is science-based, but still limited with uncertainty and many sources of errors. All of these limitations also apply to Hurrevac. We are delivering information with greater precision, BUT IT DOES NOT IMPLY ACCURACY. Science is not where we would like it to be; service is outpacing the state of the science. This is in part why NHC delivers their advisory forecasts the way they do, but the need to provide more detailed local level info is pushing the envelope. Message From a Decision Making Perspective: AVOID OVER-RELYING ON DETERMINISTIC ONE SCENARIO/BEST GUEST ALONE! It is bad enough to rely in one scenario alone only without considering the issues raised so far. Be well informed about these issues and embrace a combined official forecast with probabilistic-based information.

9 D-Day Give me the Probabilities

10 Wind Speed Probability Text Product Onset Cumulative Period Probabilities (abbreviated) In addition to: - Onset Probabilities: Text - Cumulative Wind Speed Probability: Text/Graphic 11

11 What Questions do They Answer? Cumulative (Available in NHC Graphic and PWSAT#; coarse time resolution) What are the chances that tropical storm or hurricane conditions will occur between hour 00 and XX out to 120 hours/5days with this event at my location? Onset (Available in PWSAT#; coarse time resolution) What are the chances that tropical storm or hurricane conditions will begin during a particular time period at my location? 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 chances that tropical storm or hurricane conditions will be experienced during a particular period at my location? How likely is the event to happen during that period? How likely is it to last? At what values is the event becoming more plausible (likely) than just possible? We consider trend from advisory to advisory

12 Cumulative Incremental 12HR Onset

13 Onset Tropical Storm Conditions

14 Onset Hurricane Conditions

15 Threshold: 22.5% 17.5% 30% 45% 35% 25% 20% Incremental Tropical Storm

16 Threshold: 12.5% 25% 20% 15% 10% 8% 7% Incremental Hurricane

17 Local Scale Wind Speed Probabilities Consider Trend From Advisory to Advisory

18 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 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. For trend analysis from advisory to advisory for proper risk assessment.

19 Communicate RISK Cumulative: Note that chances of hurricaneforce winds at Tampa Bay and up Port Charlotte are both around 30%! Incremental Notice: highest right Tampa Port Charlotte

20 Example: Forecast Applications: Expressions of Uncertainty Advisory Time: _1500 (25-36 Hours Third Period) FRANCES (ZFP) FRANCES (Click Point) Official in 2014

21 Threat/Potential Impact Graphics Deterministic NHC track/intensity forecast used by WFO s to create local wind forecasts (location/timing specific) Example: A major hurricane approximately 36-hours from projected landfall (Hurricane Warning issued). WFO s Probabalistic NHC wind probabilities also incorporated to produce Impact Graphics NHC 34 kt probability NHC NHC 64 kt probability

Threat/Potential Impact Graphics Official Forecast Actual

onset of the warning period (~ 36 hours).

also. Notice implicit use of probabilistic information.

22 Threat/Potential Impact Graphics Official Forecast Actual Threat/Potential Impacts Example: Approaching major hurricane at the onset of the warning period (~ 36 hours). Remember to consider the trend with these from advisory to advisory also. Notice implicit use of probabilistic information FLGHC QUESTION: When advocating the measure of protective actions according to wind impacts, which is better?

Decision Making Guide Storm Intensity Neal Batista Cat 3 (96-113 Kt)

23 Decision Making Guide Storm Intensity Neal Batista Cat 3 ( Kt) Threat? OR FORECAST VALID XX/XX00Z 31.4N 77.5W MAX WIND XXX KT...GUSTS XXX KT.

24 Clearance Times Neal Batista Forecast impact 33hrs? Available 2012 season FORECAST VALID XX/XX00Z 31.4N 77.5W MAX WIND XXX KT...GUSTS XXX KT.

25 Neal Batista Wind Probabilities 64Kt Incremental wind prob 25%?

26 More on Trend Wilma Example Impact Graphics use implicitly probabilistic guidance. What about their trend from advisory to advisory also? Advisory 30 Advisory 31 Advisory 32 Advisory Tropical Workshop

27 Take Away Be aware of the data upon which you base your decisions (whether national or local): Your NWS office can help you 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

28 Questions Pablo Santos Meteorologist In Charge NWS Miami/South Florida Forecast Office

Probabilistic Hurricane Storm Surge A Local Perspective

Probabilistic Hurricane Storm Surge A Local Perspective Florida Governor Hurricane Conference May 11-16 2014 2014 FLGHC TS 22 Pablo Santos Meteorologist In Charge NWS Miami/South Florida Forecast Office