Ivan's Analysis of Hurricane Zeta (V.2)

MHC Analyses of Tropical Cyclones

Hurricane Zeta (2020)

''Zeta making landfall in Louisiana at peak intensity, as viewed from the ISS. At the time, it was a category three hurricane on the Saffir Simpson Scale.''

Dates: October 24th- November 2nd (Post tropical after October 29th)

Hurricane Zeta

Zeta was a rare and destructive category three hurricane that made two landfalls: one on the Yucatan peninsula, as a category one, and one new Cocodrie, Louisiana, as a borderline category three hurricane.

Synopsis

The origins of Zeta were particularly complex and long in the making. The NHC first noted Zeta’s precursor disturbance a full ten days before the storm was named, which may be a record, for the longest time between the notation of an area to watch, and its formation. The disturbance stayed at a low  chance of development for six full days, before being yanked off the outlook entirely. (This was due to perceived unfavorable conditions around it, including strong upper-level winds.)

However, its forecast track shifted to the West, and, as conditions were more favorable there, was re-added to the NHC outlook just a day later, with, once again, a 20% chance of development. This time, however, the formation chances did steadily increase, and, at 6:00 UTC on the 24th of October, the NHC designated it Tropical Depression Twenty-Eight. Just 12 hours later, it strengthened into a tropical storm, and was given the name Zeta.

Despite fairly favorable conditions, Zeta did not immediately strengthen. In fact, it’s possible that it weakened back to a tropical depression briefly, though this has not been confirmed. However, once wind shear around the storm began to let up, it began to organize quickly, becoming a hurricane late on the 26th. The storm reached its initial peak intensity of 80 mph, though its pressure continued dropping until landfall on the Yucatan.

At 04:00 UTC on the morning of the 27th, Zeta made landfall on the Yucatan Peninsula, with winds of 80 mph and a pressure around 977 millibars.

Zeta making landfall on the Yucatan, portraying a very good satellite appearance.

After landfall, Zeta weakened significantly, down to a 65 mph tropical storm. (This was due to dry air becoming entangled in its circulation, and land interaction.) However, a large upper level low, which, at that point was centered over Oklahoma, began dragging Zeta Northward at a rapid pace. This caused baroclinic forcing to occur, which led to rapid strengthening. The renewed trend of intensification was very surprising, especially as it was traveling through 25 Celsius (77 fahrenheit) waters, supposedly too cold for strengthening. At 06:00 UTC on the 28th, Zeta became a hurricane again. By 6:00 PM that same day, it was a category two, still strengthening. Just before landfall, Zeta reached peak intensity as a major hurricane, with winds of 115 mph, and a pressure near 967 millibars.(Officially 110/970)

This picture shows Zeta making landfall in Louisiana, while undergoing heavy baroclinic forcing from the low centered over Oklahoma.

The storm passed over New Orleans as a 110 mph category two (officially 105) before rocketing off towards the Northeast. Just before turning extratropical over West Virginia, Zeta reached a speed of 46 mph, making it the fastest moving storm since Leslie of 2018. The remnants of Zeta became an extratropical cyclone, which later brought winds and rain to the British Isles.

Damages and Deaths

In total, Zeta caused 8 deaths and around $3.6 billion in damage. The comparatively low tolls may be related to Zeta’s fast movement, meaning the worst impacts were over quickly.

Evidence for Category Three Intensity

Surface Observations

On the ground, at least two locations reported sustained winds of major hurricane intensity. Both of the locations were ships located just offshore of the coast, where, at an altitude of 40 feet above the ground, sustained winds of 118 mph were recorded. Reducing a little for the height, it correlates to approximately 115 mph on the surface, or category three intensity. As well as that, multiple gusts into the 130s were recorded and verified on land, something typically seen in major hurricanes. Those same ships also recorded a pressure of 967 millibars, putting the pressure as much 3 millibars below the official analysis.

Reconnaissance Aircraft Observations

Though recon flights were not able to enter Zeta just prior to landfall, observations found around an hour before were still supportive of major hurricane intensity, with the highest flight level wind recorded being 136 mph. This, using 85% reduction, equates to surface winds of 115 mph, backed up by the ship observations. As well as this, several SFMRs supporting category three intensity were collected, with the highest being 107 knots (123 mph). This was flagged as suspect due to shoaling, however.

Satellite Observations

Most Dvorak observations were supportive of major hurricane status, with some, going as high as 120 mph. As well as that, AMSU also supported category three strength.

Damage Observations

Though many say damage is not a usable tool in TC analysis, I must mention the severe damage that occurred in some towns on the Louisiana shore. In communities such as Grand Isle and Chauvin, the wind was strong enough to make houses come apart and fly off, something not typically seen in category two storms.

Very severe damage in Grand Isle after Zeta.

Records: Latest US major hurricane strength lasndfall in a calendar year (beats Wilma of 2005 by 5 days)

Earliest 27th named storm on record (beats Zeta 2005)

In Summary

I believe Zeta peaked as a 115 mph category three hurricane with a pressure of 967 millibars because:

1: Surface observations supported  this intensity and pressure.

2: Aircraft recon supported winds of around 115 mph, as well as a pressure in the 960s.

3: Satellite estimates supported a major hurricane.

4: Damage in Louisiana appeared to be worse than what a category two storm would normally cause.

Official Intensity: 110/970

My Analysis: 115/967

Official Intensity at the Yucatan landfall: 80/977

My Analysis: 80/977

Official Intensity at the Louisiana landfall: 110/970

My Analysis: 115/967

NOAA recon plot for Zeta, showing an area of flight level category-four strength winds.

The track of Hurricane Zeta, by my analysis.