End of a busy 2020 Atlantic hurricane season

1 June-30 November 2020

Region

Atlantic Ocean

Satellites

MSG, Metop-C, GOES-16

Instruments

SEVIRI, ABI, AVHRR

Channels/Products

Airmass RGB, AVHRR, Sea Surface Temperature, Tropical Airmass RGB, Visible Channel, Water Vapour 6.2 microm

The 2020 North Atlantic hurricane season was record-breaking, with 30 named tropical storms. For only the second time in history, the Greek alphabet had to be used to name the final storms.

Last Updated

24 March 2023

Published on

26 October 2020

By Mark Higgins, Jochen Kerkmann, Ivan Smiljanic

The North Atlantic hurricane season officially lasts from 1 June to 30 November, with May being the least active month and September being the most active. In 2020 there were so many tropical storms that the National Hurricane Center, which names them, ran out of letters and had to start using the Greek alphabet. Of the 30 nine were named using the Greek alphabet, beating the previous record from 2005.

Out of the 30 named storms 13 developed into hurricanes, and six further intensified into major hurricanes, with one, Hurricane Iota, attaining Category 5. Twenty-seven established a new record for the earliest formation by storm number. Twelve storms made landfall in the contiguous United States, breaking the record of nine set in 1916.

Fueled up additionally by the La Nina phase (reduced wind shear), weaker easterly trade winds (reduced upwelling) and monsoon in northwest Africa (production of atmospheric waves), the season was also the fifth consecutive season in which at least one Category 5 hurricane formed. The season was also the only one with two major hurricanes in November.

Rapid intensification was observed in 10 tropical cyclones in 2020 season, tying that to season 1995. And in many instances intensification was very rapid (e.g. hurricane Eta with wind speed increase of 130km/h in only one day). Rapid intensification, together with stalling in forward motion of systems, is trend that was observed in recent hurricane seasons. Both effects contribute negatively to storm prediction and mitigation actions.

Perhaps also unique to this hurricane season is the joint view on six storms in one full-disc satellite view on 14 September 2020.

GOES-16 Cloud Type RGB — Figure 1: GOES-16 ABI Cloud Type RGB on 14 September 2020 18:00 UTC. Full disc view from only one satellite imager revealing six different tropical storms in various locations and stages of development.

The last four storms of the season were Zeta, Eta, Theta and Iota. Zeta, Eta and Iota stayed in the western part of the basin, while Theta formed in cooler waters further North and moved East over the Azores.

Theta

11-13 Nov, Azores
By Mark Higgins

According to the National Hurricane Center, Theta is the record breaking 29th storm of this North Atlantic hurricane season.

Figure 2 shows the storm at 09:00 UTC on 11 November 2020. In this water vapour image the storm is seen as the rotation in the centre.

Met-11 WV 10 Nov 2020 09UTC — Figure 2: Storm Theta seen from Meteosat-11 at 09:00 UTC on 10 November 2020

The National Hurricane Centre chart shows the initial storm location (Figure 3).

Figure 3: NOAA National Hurricane Centre forecast chart for Subtropical Storm Theta

This storm formed very late in the hurricane season, and quite far north. It formed in an area of cooler sea surface temperatures, as can be seen in Figure 4.

Tropical Airmass RGB and the Sea surface temperature from the accumulated products from AVHRR — Figure 4: Subtropical Storm Theta - the clouds are from the Tropical Airmass RGB and the Sea Surface Temperature from the accumulated products from AVHRR

The warmer waters are shown in red/orange (28-29 degrees), the cooler area (yellow) is still warm enough at 25 degrees to supply energy to sustain the storm.

Theta subsequently since travelled north-east and on 13 November was just off the coast of the Azores (Figure 5).

Theta a seen with the AVHRR instrument onboard Metop-C - at 0930 UTC on 13 November 2020 — Figure 5: Theta as seen with the Metop-C AVHRR instrument,13 November 2020 09:30 UTC

Iota

15 Nov, Atlantic Ocean
By Mark Higgins

Hurricane Iota was the 30th and final named storm of the Atlantic Hurricane season. This was the second major hurricane to form in November, following Storm Eta. The storm formed over relatively warm waters (29 degrees) which enabled the storm's intensification as it moved west.

compare1 — Figure 6: Hurricane Iota at 14:30 UTC on 15 November 2020 from Metop-C AVHRR (left) and with Sea Surface Temperatures derived from the AVHRR infrared data (right)

compare2 — Figure 6: Hurricane Iota at 14:30 UTC on 15 November 2020 from Metop-C AVHRR (left) and with Sea Surface Temperatures derived from the AVHRR infrared data (right)

Zeta

26 Oct, Gulf of Mexico

Hurricane Zeta was relatively weak system that passed the Gulf of Mexico with not much intensification prior to landfall. Figure 7 shows the topography of high reaching clouds of Central Cold Cover feature (CCC), indicating in fact a weak development of this storm.

High reaching central clouds of the Zeta hurricane seen through 500 m resolution of GOES-16 ABI VIS0.64 channel — Figure 7: High reaching central clouds of the Zeta hurricane seen through 500m resolution of GOES-16 ABI VIS0.64 channel

At the same time, Hurricane Epsilon moved northwards and entered the polar jet stream region. Curved band pattern in Figure 8, looking like and artist's impression of a big ocean wave, is seen through the Airmass RGB imagery. Compared are GOES-16 and Meteosat-11 views at the moment when the center of the system was just halfway between two satellites (longitude-wise, at 37.6 deg West).

The Meteosat-11 Airmass RGB animation in Figure 9 shows very fast advection of the system eastwards in main zonal stream, with limited relative rotation around the centre of the system. It subsequently disintegrated from its original spiral shape (with the introduction of cold and dry Arctic air from the back side of the storm), ending post-tropical transition.