The “Perfect Storms” of 1991: Multiscale Linked Cyclones Jason M. Cordeira and Lance F. Bosart Dept. of Earth and Atmospheric Sciences University at Albany/SUNY 14th Cyclone Workshop 2126 September, 2008 Sainte-Adèle, Quebec Bosart@atmos.albany.edu || Cordeira@atmos.albany.edu NSF Support #ATM-0304254 and #ATM-0553017

Previous presentation focus: Introduction 18Z/29 Previous presentation focus: Anomalous flow amplification prior to the “Perfect Storm” (PS) originating from within the North Pacific basin Current presentation focus: Developmental aspects of Hurricane Grace (HG), the PS, and Extratropical Cyclone 1 (EC1) 12Z/30 19Z/1

The extratropical transition (ET) of HG Outline [overview] Part I: The extratropical transition (ET) of HG Part II: EC1 two-stage cyclogenesis* *Gyakum et al. 1992 a. Diabatic Rossby Vortex (DRV) e.g. Moore and Montgomery 2004, 2005 b. Arctic PV anomaly interaction Part III: Tropical transition (TT) of PS into the “Unnamed Hurricane” 31/00 01/00 EC1 04/00 30/00 29/00 31/00 02/00 PS 30/00 01/00 29/00 28/00 Hurricane Grace (HG) 27/00 26/00 Tracks and 500-hPa mean height All plots, unless otherwise noted, ECMWF-ERA40 1.125

 Outline [overview] Part I: The extratropical transition (ET) of HG Part II: EC1 two-stage cyclogenesis* *Gyakum et al. 1992 a. Diabatic Rossby Vortex (DRV) e.g. Moore and Montgomery 2004, 2005 b. Arctic PV anomaly interaction Part III: Tropical transition (TT) of PS into the “Unnamed Hurricane” 31/00 01/00 EC1 04/00 30/00 29/00 31/00 02/00 PS 30/00 01/00 29/00 28/00 Hurricane Grace (HG) 27/00  26/00 Tracks and 500-hPa mean height All plots, unless otherwise noted, ECMWF-ERA40 1.125

00Z/28 PS HG Part I: The ET of HG [850 hPa] PS: Frontal vorticity structure Weak wind field HG: Barotropic vorticity structure Asymmetric wind field >30 kts >40 kts >50 kts HG 850-hPa  (105 s1), Wind (kt), 1000700-hPa THK (dam)

12Z/28 PS EC1 HG Part I: The ET of HG [850 hPa] PS: Increased spatial coverage and magnitude of northerly winds HG: “Break-away lobe” of vorticity along weak thickness gradient EC1 “embryo” PS EC1 >30 kts >40 kts >50 kts HG 850-hPa  (105 s1), Wind (kt), 1000700-hPa THK (dam)

00Z/29 PS EC1 HG Part I: The ET of HG [850 hPa] PS: Rapid expansion and magnitude increase of wind field HG: Asymmetric vorticity distribution typical of ET EC1 vorticity increase PS EC1 >30 kts >40 kts >50 kts HG 850-hPa  (105 s1), Wind (kt), 1000700-hPa THK (dam)

12Z/29 EC1 PS HG Part I: The ET of HG [850 hPa] PS: Continued increase and expansion of wind field to 5070+ knots HG: ET nearly complete EC1 rapid vorticity generation 50+ knot southerly winds in warm sector EC1 PS HG >30 kts >40 kts >50 kts 850-hPa  (105 s1), Wind (kt), 1000700-hPa THK (dam)

12Z/29 EC1 PS HG Part I: The ET of HG [Precip. Water] PS and HG: Poleward surge of tropical (40+ mm) precipitable water values EC1 PS HG 850-hPa  (105 s1), Wind (kt), Precipitable Water (mm)

N S 12Z/29 EC1 PS HG Part I: The ET of HG [Precip. Water] PS and HG: Poleward surge of tropical (40+ mm) precipitable water values Cross section perpendicular to PS warm front, through EC1, along 51.5W EC1 PS S HG 850-hPa  (105 s1), Wind (kt), Precipitable Water (mm)

Part II: EC1 two-stage cyclogenesis [a. DRV] Deep moisture Potential instability Moist absolutely unstable layer (700-300-hPa) e 334 336 338 340 K  [K] P to 300 [hPa] Cold / Dry SLP Warm / Moist N e [K],  [K], Wind [kt] S

e [K], Vertical Velocity [b s-1] Part II: EC1 two-stage cyclogenesis [a. DRV] 334 336 338 340 K Deep moist ascent Large in the ‘PBL’ P to 300 [hPa] Vertical Velocity ~20 b s1 Cold / Dry SLP Warm / Moist N e [K], Vertical Velocity [b s-1] v.v. max. S

e [K], Relative Vorticity [104 s1] Part II: EC1 two-stage cyclogenesis [a. DRV] 334 336 338 340 K Strong low-level  below v.v. maximum P to 300 [hPa] Relative Vorticity Cold / Dry SLP Warm / Moist N e [K], Relative Vorticity [104 s1] v.v. max. S

e [K], Diabatic Heating Rate [K day1] Part II: EC1 two-stage cyclogenesis [a. DRV] Instantaneous diabatic heating > 100 K day1 334 336 338 340 K P to 300 [hPa] Cold / Dry SLP Warm / Moist v.v. max. N e [K], Diabatic Heating Rate [K day1] S heating max.

PV [PVU], Instantaneous PV Tendency [PVU 6 h1] Part II: EC1 two-stage cyclogenesis [a. DRV] Low-level PV maximum + () lower (upper) PV Tendency 1.5 2.0 2.5 PVU v.v. max. P to 300 [hPa] heating max. Max: 10 PVU 6 h1 PV SLP N PV [PVU], Instantaneous PV Tendency [PVU 6 h1] S

PV [PVU], Instantaneous Diabatic Heating [K day1], V-wind Part II: EC1 two-stage cyclogenesis [a. DRV] 1.5 2.0 2.5 PVU W E P to 300 [hPa] Diab. Heating Diab. Heating V-wind PV W PV [PVU], Instantaneous Diabatic Heating [K day1], V-wind E

L Part II: EC1 two-stage cyclogenesis [a. DRV] A B B x x A A B x 36-hour backward trajectories 900600-hPa within 4045N and 5055W PV > 1.5 PVU… Pressure: Representative trajectories ending 12Z/29: A B 7h B L x 6 12 Hours PV: x 36h A A B x B: Intersects bottom boundary at 7h 6 12 Hours A: Trajectory #84 B: Trajectory #33 surface warm front

PS EC1 HG Part II: EC1 two-stage cyclogenesis [a. DRV] Deep moist convection along PS warm front: Characteristic of DRV? PS Meridional winds of 2025 m s1 established frontal ascent of 20 b s1 Deep moist ascent and subsequent diabatic heating promoted rapid low-level: Relative vorticity growth PV production What becomes of EC1? EC1 Jay jay HG 29 October 1401 UTC

EC1 PS Part II: EC1 two-stage cyclogenesis [b. PVF] Hurricane Grace 31/00 01/00 30/00 PS 29/00 31/00 02/00 30/00 01/00 29/00 28/00 Hurricane Grace 27/00 26/00

EC1 PS Part II: EC1 two-stage cyclogenesis [b. PVF] 999 hPa L 31/00 01/00 GIBBS 30/00 PS 29/00 31/00 02/00 30/00 01/00 29/00 28/00 Hurricane Grace 27/00 26/00

EC1 PS Part II: EC1 two-stage cyclogenesis [b. PVF] 999 hPa Hurricane Grace L 31/00 01/00 GIBBS 30/00 PS 29/00 31/00 02/00 949 hPa 30/00 01/00 L 29/00 28/00 Hurricane Grace 27/00 26/00 GIBBS

PVF EC1 How did EC1 respond to PVF? Part II: EC1 two-stage cyclogenesis [b. PVF] dd 00Z 12Z PVF 24 25 31 26 27 28 30 29 10;-125;25;30, str/90;-95;0 30 EC1 How did EC1 respond to PVF?

PVF EC1 How did EC1 respond to PVF? Part II: EC1 two-stage cyclogenesis [b. PVF] dd 00Z 12Z PVF E 24 25 31 Cross Section at 12Z/30 26 27 28 30 29 30 W EC1 How did EC1 respond to PVF?

Part II: EC1 two-stage cyclogenesis [b. PVF] Interacting low-level and upper-level PV maxima 1.5 2.0 2.5 PVU P to 300 [hPa] PVF Cold Core Warm Core EC1 SLP W  [K], PV [PVU] E

Vertical Velocity [b s1] , PV [PVU] Part II: EC1 two-stage cyclogenesis [b. PVF] Tropospheric deep ascent 1.5 2.0 2.5 PVU P to 300 [hPa] PVF EC1 v.v. max. SLP W Vertical Velocity [b s1] , PV [PVU] E

Relative Vorticity [104 s-1] , PV [PVU] Part II: EC1 two-stage cyclogenesis [b. PVF] Low-level vorticity maximum Collocated vorticity structure 1.5 2.0 2.5 PVU P to 300 [hPa] PVF 850-hPa W E EC1 v.v. max. SLP W Relative Vorticity [104 s-1] , PV [PVU] E

Instantaneous Diabatic Heating [K day1], PV [PVU] Part II: EC1 two-stage cyclogenesis [b. PVF] Instantaneous diabatic heating ~ 100 K day1 1.5 2.0 2.5 PVU P to 300 [hPa] PVF heating max. EC1 v.v. max. SLP W Instantaneous Diabatic Heating [K day1], PV [PVU] E

Instantaneous PV tendency [PVU 6 h1], PV [PVU] Part II: EC1 two-stage cyclogenesis [b. PVF] + () lower (upper) PV Tendency 1.5 2.0 2.5 PVU P to 300 [hPa] PVF heating max. EC1 v.v. max. SLP W Instantaneous PV tendency [PVU 6 h1], PV [PVU] E

L Part II: EC1 two-stage cyclogenesis [b. PVF] F36 F30 F24 x B x A F18 36-hour backward trajectories 900-600-hPa within 4954N and 1924W PV > 1.5 PVU… Pressure: F36 Representative trajectories ending 12Z/30: 36h F30 F24 x B x A F18 F12 A x L F6 F 12 24 Hours L6 PV: L12 L24 L18 B x B x A x 36h 12 24 Hours A: Trajectory #4 B: Trajectory #46

Part II: EC1 two-stage cyclogenesis [b. PVF] EC1 - feature following time-height 2.5 radius average 400 PV 500 300-K  600 Pressure (hPa) 296-K  700 20 Vertical Velocity 25 20 292-K  800 15 1.5 2.0 2.5 3.0 PVU 900 1000 Sea Level Pressure 00Z 28 12Z 28 00Z 29 12Z 29 00Z 30 12Z 30 00Z 31 12Z 31 00Z 01 12Z 01 HG Lobe DRV PVF Interaction

Summary: Part I (The ET of HG) The ET of HG influenced the evolution of the PS and EC1 through the poleward transport of: Tropical moisture perpendicular to the PS warm front Antecedent low-level vorticity

Summary: Part II (EC1 two-stage cyclogenesis) Deep moist ascent/convection occurred in association with strong frontal lift and resulted in Diabatic low-level PV production Formation comparable to a DRV and “stage 1” cyclogenesis EC1 DRV subsequently phased with Arctic PV anomaly (PVF) and resulted in A second period of low-level PV production SLP decrease of 50 hPa in 24 hours consistent with “stage 2” cyclogenesis

Additional Slides:

1200 UTC 28 October Infrared Satellite

44N;51.5W 12Z/29

The warm seclusion of the PS was promoted Summary: Part III (The TT of the “Perfect Storm”) The warm seclusion of the PS was promoted In the presence of large-scale deformation (e.g. zonal axis of dilatation) Schultz et al. 1998 Preferred frontogenesis pattern (suggested) with the ET of HG Harr and Elsberry 2000, Sinclair 2002 The TT of the PS was influenced by Low-level warm-core vortex following the warm seclusion of the PS Minimal DT850-hPa shear (not shown)