Caption: Figure 5: Distribution of absolute vorticity at 8km on June 27: (a) 07:00; (b) 08:00; (c) 09:00; (d) 10:00; (e) 11:00; (f) 12:00; (g) 14:00; (h) 16:00; (i) 17:00; (j) 18:00; (k) 19:10; (l) 20:00.
Caption: Figure 6: Vertical distribution of absolute vorticity at 32.1[degrees]N on June 27: (a) 07:00; (b) 09:00; (c) 11:00; (d) 13:00; (e) 13:10; (f) 13:20; (g) 13:30; (h) 14:00; (i) 14:30; (j) 15:00; (k) 15:10; (l) 15:30; (m) 16:30; (n) 17:30; (o) 19:10; (p) 21:30.
A TC tends to move toward the area of maximum relative vorticity tendency, which within most of the troposphere (850-300 hPa) is mainly contributed by the advection of absolute vorticity. The advection of relative vorticity is essentially steering.
For example, newer formulations use subsets of these factors and obtain more variability explained, while others have combined factors together (such as 1 and 6 together as absolute vorticity) or have replaced ingredients with a more physically based factor (such as substituting in potential intensity for 4; Emanuel and Nolan 2004; Camargo et al.
advection by geostrophic wind in 500 hpa level and 1000/500 thickness advection by geostrophic wind of 1000 hpa level can interpret development or decline of the system pressure.
Evaluation of 500-hPa geopotential height and absolute vorticity
fields from the Eta model between 1800 UTC 11 January and 1200 UTC 12 January 2004 (Figures 3(a)-3(d)) revealed a shortwave trough that transited from central Minnesota to central Pennsylvania and generally weakened as it did so.