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Keywords:

  • tropical storms;
  • hurricanes;
  • storm tracks;
  • morphometry;
  • sinuosity;
  • North Atlantic

ABSTRACT

Quantitative analysis is carried on the shape of over 420 tropical storm and hurricane tracks in the North Atlantic basin for the period 1965–2011. A sinuosity metric is used as the basis for track morphometry, applied to best-track data accessed from the IBTrACs archive maintained by NOAA. GIS tools, track mapping according to sinuosity category, and various statistical analyses permit temporal and spatial patterns in track shape to be identified and investigated. Temporal analysis reveals no underlying long-term trend in track sinuosity over the past 4.5 decades, implying an absence of climatic-change forcing on storm migration behaviour at the basin scale. Instead, large inter-annual variability dominates, although it is possible to observe episodes of notable cyclic swings in average sinuosity towards straighter or more sinuous tracks. Seasonality in track behaviour is pronounced, as similarly reported for other ocean basins. Predictable straight and quasi-straight track types are more common (64–100%) during the early months (May to July) of the hurricane season, with this reversing at the peak and later phase of the season (September, November) to a predominance for quasi-sinuous and sinuous tracks (58–70%). In spatial terms, track morphometric analysis according to 10° longitudinal zone of cyclogenesis is valuable, revealing that storm origin is reasonably indicative of likely track shape over the subsequent lifespan. Thus, while 62–68% of storms spawned west of 80°W in the Caribbean Sea – Gulf of Mexico region show a tendency to follow straighter tracks, 67–72% of storms formed east of 40°W in the central-eastern North Atlantic subsequently describe more sinuous tracks. Overall, these patterns are seen to influence the geographic potential of storm landfall. This is important for societal vulnerability on coastlines at risk, since storms exhibiting higher track sinuosity generally prove to survive longer, migrate farther and therefore display greater potential for inflicting damage over wider areas.