1. A Brief Digression: Waterspouts Szilagyi (2005, 2009) Waterspout Nomogram 850 hPa T: ~3-7°C SST: ~19-21°C

2. A Brief Digression: Waterspouts GRB 1200 UTC 11 Sep 2015 sounding, modified for N. Lake Michigan buoy SST/surface T d LFC: 3112 ft EL: 18541 ft EL-LFC: 15429 ft (on the edge of the ‘favorable’ region for waterspouts) Other Parameters: surface vorticity (SPC Mesoanalysis)

3. Toward Improved Tropical Cyclone Intensity Estimates During Extratropical Transition Clark Evans // Friday Weather Discussion // 11 Sept. 2015 Collaborators: Tim Olander (UW-CIMSS), Chris Velden (UW- CIMSS), Bob Hart (FSU)

4. What is Extratropical Transition? Klein et al. (2000, Wea. Forecasting), their Figure 5 The transformation of an initially warm- cored tropical cyclone into an asymmetric, nominally cold-cored extratropical cyclone.

5. What is Extratropical Transition? Jones et al. (2003, Wea. Forecasting), their Figure 11

6. Estimating TC Intensity Atlantic: ~30% reconnaissance aircraft (near land), ~70% remotely-sensed methods –Scatterometry, microwave imagery, Dvorak technique Elsewhere: ~100% remotely-sensed methods Rarely do TCs pass directly over a buoy, oil rig, ship, coastal weather station, or METAR site. Statistics: Landsea and Franklin (2013, Mon. Wea. Rev.)

7. The Dvorak Technique Dvorak (1984), their Figure 5

8. The Dvorak Technique Velden et al. (2006, Bull. Amer. Meteor. Soc.), their Figure 1 and Table 2 (constraint)

9. The Dvorak Technique Velden et al. (2006, Mon. Wea. Rev.), Fig. 9; from Brown and Franklin (2004)

10. The Advanced Dvorak Technique Reference: Olander and Velden (2007, Wea. Forecasting) Objective extension upon the Dvorak technique. –Objective storm-center determination. –Objective scene type determination. –Cloud pattern relationships with TC intensity regression-based rather than empirical. Quality of intensity estimates not dependent upon the skill/training of the end-user. –ADT skill comparable to that of DT in the Atlantic.

11. The Advanced Dvorak Technique ADT FlowchartScene Selection http://tropic.ssec.wisc.edu/misc/adt/info.html

12. The Challenge There exist relationships between intensity and cloud patterns for tropical cyclones. These relationships are less reliable during extratropical transition (ET). –The cyclone’s energetics change during ET from surface heat exchange to the vertically-sheared flow. –Baroclinic energetics typically maintain intensity to a greater extent than the DT or ADT estimate. –Unclear that intensity and cloud patterns are related to any meaningful extent for non-tropical cyclones.

13. The Challenge Representative sample: ADT intensity estimates for TCs within two days of completing ET. –12 N. Atlantic TCs, n = 18 observations –Verification: reconnaissance or landfall intensity data Maximum sustained wind statistics: –Root Mean Squared Error: 14.26 kt –Bias: -13.12 kt (weak bias) –Larger than typical for DT and ADT but comparable to uncertainty in satellite-derived best-track estimates. Manion et al. (2015, Wea. Forecasting)

14. Preliminary Research Manion et al. (2015, Wea. Forecasting), their Figure 14a,b Can ADT performance during ET be evaluated via model- derived intensity time series and synthetic satellite imagery?

15. Preliminary Research Quantitative insight not possible due to substantial sensitivity to microphysics. Qualitative insight possible, however, given reasonable agreement with observed sample. –Error and bias largest early in ET (“actual” intensity still high, ADT-inferred intensity low). –Error and bias larger for stronger TCs (greater possible discrepancy between intensity estimates). –The “shear” scene type is predominant owing to increasingly environmental shear during ET.

16. One Way Forward We propose an ET intensity adjustment, or an empirical bias correction, within the ADT. We also considered a new ET scene type, but other similar attempts have not been successful. –“XT” method (Miller and Lander 1997) –Non-tropical cyclones (Smigielski and Mogil 1992) –Subtropical cyclones (Hebert and Poteat 1975)

17. What is Needed? Trigger: is the tropical cyclone undergoing ET? We utilize a three-part trigger: –Latitude: is the TC poleward of 20°N or 15°S? –Satellite: have ≥ 50% of ADT scene types been “shear” over the past 12 h? –Structure: has the TC’s lower tropospheric thermal structure become sufficiently asymmetric? Required to be met for two consecutive forecast times (6-h and 12-h) given data latency.

18. The Trigger Evans and Hart (2003, Mon. Wea. Rev.); Hart (2003, Mon. Wea. Rev.) (over a radius of 5° from TC center; h = 1 for N. Hemisphere) Onset of ET: B > 10 m (Evans and Hart 2003)

19. What is Needed? Adjustment: by what amount to adjust intensity? Currently: adjust ADT final intensity upward by 1 T-number. –Adjustment is blended; zero when trigger activated, linearly increases to 1 T-number 12 h later. –Takes advantage of non-linearity of T-number scale. –As TC intensity generally decreases during ET, this accounts for both intensity- and time-dependence.

20. The Adjustment Velden et al. (2006, Bull. Amer. Meteor. Soc.), their Table 2 ∆v max = 5 kt ∆v max = 15 kt ∆v max = 20 kt Intensities not typically observed as a TC undergoes ET.

21. Demonstration Operational ADT: http://tropic.ssec.wisc.edu/real-time/adt/adt.html Experimental ADT with ET Adjustment: http://tropic.ssec.wisc.edu/real-time/adt/ET/ http://moe.met.fsu.edu/cyclonephase/cimss/data/ (Only in current form for a few W. Pacific TCs.)

22. Case Study: 15W (Molave) No Adjustment: CI 1.5 (v max 25 kt) With Adjustment: CI 2.5 (v max 35 kt) ASCAT-A: > 40 kt ASCAT-A data from NOAA/NESDIS Track from Unisys

23. Case Study: 17W (Atsani) No Adjustment: CI 1.7 (v max 27 kt) With Adjustment: CI 2.7 (v max 39 kt) ASCAT-A: > 55 kt ASCAT-A data from NOAA/NESDIS Track from Unisys

24. Case Study: 08L (Henri) Cases where the GFS depiction of the TC is weak (here) or inaccurate are not handled well by our trigger. http:// moe.met.fsu.edu/cyclonephase /

25. Discussion Ultimate goal: improved real-time TC intensity estimates during ET (research to operations). –Improved assessment of higher-latitude impacts. –More reliable best-track intensity estimates. Could we be doing things differently than we are presently doing them? Ideas welcome!