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Thomas Galarneau 1 , Chris Davis 1 , Bill Kuo 1,2,3 , and Xingqin Fang 2

Diagnosis of GFS Height, Wind, and TC Motion Errors during the 2012 North Atlantic Hurricane Season. Thomas Galarneau 1 , Chris Davis 1 , Bill Kuo 1,2,3 , and Xingqin Fang 2. 1 Mesoscale and Microscale Meteorology Division, NCAR Earth System Laboratory, Boulder, CO

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Thomas Galarneau 1 , Chris Davis 1 , Bill Kuo 1,2,3 , and Xingqin Fang 2

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  1. Diagnosis of GFS Height, Wind, and TC Motion Errors during the 2012 North Atlantic Hurricane Season Thomas Galarneau1, Chris Davis1, Bill Kuo1,2,3, and Xingqin Fang2 1Mesoscale and Microscale Meteorology Division, NCAR Earth System Laboratory, Boulder, CO 2UCAR COSMIC Program, Boulder, CO 3Developmental Testbed Center, Boulder, CO 31st Conference on Hurricanes and Tropical Meteorology San Diego, California–4 April 2014 HFIP sponsored project through the DTC

  2. Purpose • Document an initial effort to examine deterministic GFS forecast wind errors • Emphasis on longer range (day 5+) • Examine seasonal mean (1 August–31 October) GFS forecast wind errors for 2012 • Dynamic tropopause (2.0 PVU surface) • Energetics • Present a brief analysis of Hurricane Sandy • Early forecasts “out to sea”

  3. Track Error Statistics 2012 North Atlantic Season • Relative increase in [d(error)/dt]GFS at day 4+ • Longer-lead forecasts marked by NE track bias • Motivates examination of synoptic-scale flow in GFS forecasts Mean Absolute Error Meridional Error (m) Track bias Zonal Error (m) Track forecasts downloaded from J. Vigh’s TC Guidance Project website

  4. GFS DT θ and Wind: 92-day Mean 1 Aug–31 Oct 2012 Analysis • Flattening of time-mean pattern with increasing lead time • Strong westerly flow extends southward to subtropics by days 4–7 96-h 168-h K

  5. GFS DT θ and Wind: 92-day Mean 1 Aug–31 Oct 2012 Analysis K DT θerror DT u Analysis 24-h 72-h 120-h 168-h Meridional profile of DT θ error and DT u-wind Loss of AWB structure Southward shift of midlatitude jet

  6. Western Hemisphere Blocking: Aug–Oct 2012 Pelly and Hoskins (2003): GFS analysis 168-h GFS forecast Blocking missed or amplitude reduced K

  7. Energetics: Eddy Kinetic Energy Compute over latitude band 20°–85°N Lorenz (1955): • Northern Hemisphere KE increases during Aug-Oct • Systematic reduction in KE in GFS forecasts • Reduction in KE increases with forecast lead • Suggests synoptic-scale eddies too weak in GFS forecasts  more difficult to maintain amplified (or even blocked) flow • Consistent with time-mean DT jet/waveguide that is more zonal in GFS forecasts GFS Forecast Northern Hemisphere Eddy Kinetic Energy Date (mmddhh)

  8. GFS 250 hPaζ, Vir, and 500 hPaω: 92-day Mean 1 Aug–31 Oct 2012 • Decrease in tropical convection overall with increasing lead; most notable over WPAC and EPAC • Decrease in irrotational wind connecting tropics and midlatitudes • Suggests connection between reduced tropical convection and decreased amplitude of midlatitude waveguide Analysis 96-h 168-h Pa s−1

  9. 00Z GFS Forecasts – TC Sandy (Oct 2012) Positions marked every 24 hours at 00Z Initial times: 20121021 20121022 20121023 20121024 20121025 20121026 20121027 20121028 20121029 20121030 HURDAT 30 GFS forecasts initialized north of Caribbean (26–29 October) moved left toward NJ 29 28 GFS forecasts initialized in Caribbean (24–25 October) moved out to sea  linked to midlatitude flow errors over North Pacific and Rockies 27 26 GFS forecasts initialized in Caribbean (21–23 October) moved out to sea  linked to wave train originating over tropical eastern Pacific 25 24 22 23 Tracks depart at 12Z/26 (84-h GFS forecast initialized at 00Z/23

  10. 850–350 hPa mean Venv and ζ at 12Z/26 Environment Wind Profile at 12Z/26 panl,pfor Reduced ridging in forecast southern vort max GFS Analysis pressure (Pa) GFS analysis Venv GFS forecast Venv ×10−5 s−1 warm frontal wave u-comp solid; v-comp dashed 84-h GFS Forecast 84-h GFS Forecast v12Z/26 Oct 2012

  11. PVU GFS Analysis remnant trough Sandy 320 K PV, pressure, and wind at 12Z/25 60-h GFS Forecast Sandy

  12. PVU GFS Analysis “roll-up” of remnant trough remnant trough Sandy 320 K PV, pressure, and wind at 12Z/26 84-h GFS Forecast Sandy

  13. PVU GFS Analysis trough core stronger and farther south than forecasted Sandy 340 K PV, pressure, and wind at 12Z/25 60-h GFS Forecast trough core farther north in forecast Sandy

  14. Subtropical Waveguide Errors Evident Early in Forecast 250 hPastreamfunction error (shaded; ×106 m2 s−1) 24-h GFS Forecast error (verifying 00Z/24 Oct 2012) GFS forecast in blue, analysis in black Cool colors=more cyclonic in GFS forecast ×106 m2 s−1 • Errors in subtropical waveguide originate over eastern Pacific and propagate downstream • Errors consistent with more zonal subtropical jet/waveguide over Gulf of Mexico/west Atlantic

  15. Final Comments • Midlatitude jet evolves to more zonal structure and shifts southward with increasing forecast lead • consistent with northeastward track bias • Decreased frequency of blocking/anticyclonic wave breaking • Reduced KE suggests synoptic-scale eddies are too weak • Early forecasts for Sandy marked by subtropical jet that was too zonal • impacted interaction of subtropical wave with low-level trough that steered Sandy northwestward on 26 Oct • It is hypothesized that reduced tropical convection over WPAC and EPAC in GFS forecasts impacts the structure of the subtropical and midlatitude waveguide

  16. Extra slides

  17. GFS DT θ and Wind: 92-day Mean 1 Aug–31 Oct 2012 Analysis K DT θerror DT u Analysis 24-h 72-h 120-h 168-h Meridional profile of DT θ error and DT u-wind

  18. GFS DT θ and Wind: 92-day Mean 1 Aug–31 Oct 2012 Analysis K DT θerror DT u Analysis 24-h 72-h 120-h 168-h Meridional profile of DT θ error and DT u-wind

  19. GFS DT θ and Wind: 92-day Mean 1 Aug–31 Oct 2012 Analysis K DT θerror DT u Analysis 24-h 72-h 120-h 168-h Meridional profile of DT θ error and DT u-wind

  20. GFS DT θ and Wind: 92-day Mean 1 Aug–31 Oct 2012 Analysis K DT θerror DT u Analysis 24-h 72-h 120-h 168-h Meridional profile of DT θ error and DT u-wind Loss of AWB structure Southward shift of midlatitude jet

  21. Tropical Convection: Aug–Oct 2012 5–15°N latitude band GFS Analysis GFS 168-h Forecast Pa s−1

  22. Vorticity Evolution: 12Z/23–28 Oct 2012 925–850 hPa layer mean relative vorticity every day at 1200 UTC contours every 4.0×10−5 s−1 starting at 4.0×10−5 s−1 20121023 20121024 20121025 20121026 20121027 20121028 warm frontal wave southern vort max GFS Analysis GFS Forecast (00Z/23 init)

  23. 00Z GFS Forecasts – TC Isaac (Aug 2012) Positions marked every 24 hours at 00Z 20120817 20120818 20120819 20120820 20120821 20120822 20120823 20120824 20120825 20120826 20120827 20120828 20120829 20120830 HURDAT 31 30 29 28 26 27 25 24 23 22 21 • GFS forecasts initialized: • Prior to 0000 UTC 24 August are too far north in eastern Caribbean. • 0000 UTC 21–25 August 2012 exhibit systematic early recurvature as Isaac approaches southern Florida. • 0000 UTC 26–31 August 2012 are improved before landfall.

  24. Dynamic tropopauseθ (K), wind (knots) and 925–850 hPa layer-mean ζ (×10−5 s−1) Forecast error in central ATL 96-h GFS Forecast Initialized at 00Z/22 Aug Trough fractures in reality, not in GFS Analysis at 00Z/26 Aug

  25. Trough Fracture due to Convection ahead of Isaac (missed by GFS) Analysis at 1200 UTC 25 Aug 2012 Predecessor rain event (PRE) that developed 24-h earlier (not in GFS forecasts) 1345Z/25 Aug 2012 84-h GFS forecast (00Z/22 init) • Divergent outflow associated with PRE decreases trough filamentation time • Trough fracture allows Isaac to move westward 300-200 hPa PV (green every 1 PVU), 300-200 hPa layer-mean irrotational wind (arrows in m/s) 250 hPa wind speed (shaded in m/s) 600-400 hPaascent (magenta contours every 0.3 Pa s-1)

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