How buoy observations of wave spectra deepen our understanding of Hurricane Ian’s dynamics

Sofar Ocean

Thumbnail and Header Photo Credit: NOAA

In late September 2022, Hurricane Ian made landfall in southwestern Florida. The Category 4 storm, which had maximum sustained winds of 155 mph, was one of the strongest hurricanes to ever hit the United States. It resulted in over 100 deaths, severe storm surge and flooding, and, prior to reaching U.S' shores, a nation-wide power outage in Cuba.

Sofar’s expansive network of Spotter smart buoys in the Gulf of Mexico collected real-time data about Ian’s intensity and location as it approached Florida. The buoys’ observations of wave spectra are particularly valuable; in a hurricane, these observations convey the distribution of wave energy as a function of direction and frequency, providing a more granular view of the wave dynamics generated by these powerful storms. Below, we analyze the observations of wave spectra collected by SPOT-010445 (Figure 1) along Ian’s outer edge as it moved through the Gulf of Mexico.

Figure 1. From left to right: a map, colored by significant wave height forecasts, showing the paths of Hurricane Ian and SPOT-010445 (yellow pentagon); a time series of the observations of significant wave height collected by SPOT-010445; a polar plot of SPOT-010445’s observations of wave spectra. The animations are synchronized and cover the period from September 27th to September 29th.

In the leftmost animation, a map colored by significant wave height shows the path of Hurricane Ian and the drift track of SPOT-010445 (yellow pentagon).

The middle animation is a time series of the observations of significant wave height made by SPOT-010445. As Ian rapidly intensifies over the Gulf of Mexico, its eastern edge passes over SPOT-010445. This moment is captured by the spike in wave height to around seven meters (~23 feet) observed by SPOT-010445 on September 28th.

Observations of significant wave height, though useful, are one dimensional. In the rightmost animation, SPOT-010445’s observations of wave spectra expand our understanding of Hurricane Ian’s wave dynamics. The polar plot shows:

  • Direction: The polar coordinates indicate the direction that the waves are traveling to. As Ian makes its way around Cuba, the wave energy points northwest; then, as it enters the Gulf and turns towards Florida, its direction shifts to the north and east.
  • Frequency: The radius of the polar plot shows the wave frequency. When the wave energy is closer to the center of the plot, the frequency is lower; when the wave energy is further from the center, the frequency is higher. SPOT-010445 observed a dominant wave frequency of 0.1 Hz, or a wave period of 10 s.
  • Energy: The colored areas in the polar plot convey wave energy, with warmer colors representing more energetic waves. The polar plot captures a simultaneous increase in wave energy and shift in direction of the largest waves on September 28th. Since Hurricane Ian traveled northeast after passing Cuba and northern hemisphere hurricane winds circulate in a counter-clockwise direction, the largest and most energetic waves should be in the storm’s front right quadrant, where the wind and storm direction align. However, in this case, it appears that the right hand side of the hurricane was impacted by land, as the polar plot initially shows the largest wave heights on the left hand side of the storm.

Interested in learning more about wave spectra? Check out our recent blog post, which defines the components of a wave spectrum and details how Sofar assimilates wave spectra to improve its ocean weather forecasts.

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