Hurricane Zeta made landfall in Louisiana on Wednesday, October 28th with winds around 110mph and then downgraded to a Tropical Storm on Thursday, October 28th over Alabama. As Zeta continued its path northeast, the strong winds left significant damage in its wake as shown in Figure 1 below.
Figure 1: As Hurricane Zeta moved through New Orleans on Wednesday, October 28th, strong winds caused tornado-like damage blowing down a tree limb onto a powerline.
Early on Thursday, October 29th, Tropical Storm Zeta passed through Atlanta. Figure 2 below shows some of the damage that was found on Georgia Tech’s campus hours after the storm had passed through.
Figure 2: Photo taken of downed powerlines and limbs on Fowler Street NW on Georgia Tech’s Campus on Thursday, October 29th at 10:00AM.
Tropical Storm Zeta moved along its path relatively quickly due to the position of the jet stream and a midlatitude cyclone to the northwest. We can see in Figure 3 the predicted path that shows Zeta moving back over the ocean in the mid-Atlantic around Thursday evening.
Figure 3: The Hurricane Zeta advisory for Wednesday, October 28th shows the predicted path of Zeta.
Although Zeta will be moving back over the ocean, it will not be able to strengthen any because the ocean waters are not warm enough to fuel the storm. In Figure 4 below, we can see the sea surface temperatures where Zeta is going to go over are around 18 degrees Celsius which is much too cold.
Figure 4: Sea surface temperatures over the mid-Atlantic in degrees Celsius with the warmer temperatures represented by the warmer colors.
When we look at what else could result from Zeta, we can look for any areas of frontogenesis. Frontogenesis is the process of tightening horizontal temperature gradient to create and strengthen cold and warm fronts. By using sign analysis on the four terms of the frontogenesis equation, we can hypothesize whether or not it will occur. Positive terms contribute to frontogenesis, and negative terms contribute to frontolysis, the weakening of horizontal temperature gradients. The four terms are shearing, diabetic heating, tilting, and confluence. Sign analysis on the first two terms resulted in a negative shearing and a positive diabetic heating. For the tilting term, we can use Figures 5 and 6 below to arrive at an overall negative tilting term.
Figure 5: A vertical cross section showing pressure and cyclonic potential vorticity. As pressure decreases, the dark green potential temperature values increase.
Figure 6: A vertical cross section showing pressure and omega (upward vertical motion). Going from point B to point A, omega becomes more negative which indicates upward vertical motion. This combined with the analysis from Figure 5 results in a negative tilting term.
For the confluence term, we can analyze Figure 7 below resulting in a positive confluence term.
Figure 7: A 500mb Geopotential Height, Cyclonic Vorticity, and wind map with the adjusted x and y prime axes. The y prime axis points toward lower potential temperatures. In the positive y prime direction, the wind barbs change from strong winds going northeast to slightly weaker and more easterly winds. This signifies an overall positive confluence term.
Altogether, we have negative shearing, positive diabetic heating, negative tilting, and positive confluence with the positive terms slightly outweighing the negative ones. Thus, we could possibly have some frontogenesis resulting in a front.
Figure 8: This map shows fronts and weather types valid through Friday, October 30th. The red arrow points to the low-pressure system of Zeta.
In Figure 8 above, we can see the cold front that is predicted for Friday resulting from Zeta’s low-pressure system. Zeta is forecasted to continue degenerating over the mid-Atlantic.
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