Tropical Cyclone Giovanna (February 9th-21st)

Tropical Cyclone Giovanna formed in the Southwest Indian Ocean on the 9th of February 2012. It quickly organized into a tropical storm on the 9th, and then explosively intensified into a category four equivalent cyclone with a pinhole eye feature on the 10th. Giovanna immediately passed over a small coral atoll north of Mauritius and Reunion – making a direct hit, fortunately there are no permanent inhabitants on these islands.

Giovanna exhibits concentric eye-wall structure from TRMM microwave imagery - pinhole inner eyeMODIS true color satellite imagery of Giovanna's concentric eye-wall structureConcentric Eye-Wall structure visible on Reunion (MeteoFrance) Radar

(Naval Research Lab TRMM Microwave Imagery; NASA MODIS Satellite Imagery; MeteoFrance-Réunion Radar Imagery February 12th 2012)

The cyclone began to exhibit a concentric eyewall feature as an outer rainband wrapped around the very small core of the storm and began to form an outer eyewall. The inner eyewall collapsed and the outer eyewall began to take over. This was a slow process that saw Giovanna weaken to a low-end category three equivalent cyclone.

However, the next day saw a restrengthening that allowed Giovanna to regain category 4 status, and some satellite estimates using the Dvorak Technique even suggested that Giovanna had peaked at a category 5 equivalent storm with 160mph 1-minute sustained winds. However, the storm weakened at landfall due to a second eye-wall replacement cycle and it made landfall with 110-120mph winds. Madagascar’s major city centers, including the inland capital city – Antananarivo,were spared the brunt of the storm, but nonetheless it made landfall in one of the island’s most populous regions.

The storm quickly weakened due to the mountainous terrain disrupting the circulation, and up-slope winds essentially squeezing moisture from the storm. But the center managed to emerge over the Mozambique channel a shadow of its former self. Giovanna then meandered southwards, safely away from land, and then took a hard eastward turn and brushed the southern tip of Madagascar while strengthening back to a category two equivalent storm with 100mph 1-minute sustained winds.

In total, reports suggest that 33 people were killed as a result of the storm’s winds, fresh water and storm surge flooding, and post-storm conditions. A significant percent of the towns hit by the storm are reported to be destroyed.


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