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the joint Technical Note issued by CPTEC/ The existing theory that quantifies the joint the OHC content (LEIPPER and VOLGENAU, reached its negative maximum on the af-
INPE and INMET. Regardless of terminolo- contribution between the variables de- 1972), a measure of the ocean’s potential ternoon of March 21, approximately 12
gy, Ocean Heat Content (OHC) analysis is scribed by Emanuel (2007) is the Genesis to sustain the intensification of TC (HALLI- hours after the system had passed over the
a measure of the potential heat the ocean Potential Index (GPI; EMANUEL & NOLAN, WELL et al., 2008), ignored by almost all region of the highest OHC along its path
has to sustain and intensify tropical cy- 2004). Until 2020, the GPI had never been published studies on the TC Catarina (Figure 4a). This environment of strong
clones (e.g., HALLIWELL et al., 2008, SHAY used to assess Hurricane Catarina. During most of the path transit of Ca- vorticity and high humidity produced a GPI
et al., 2000; LEIPPER and VOLGENAU, Tropical cyclones (TCs) are frequent in tarina, the GPI remained high and above peak that probably influenced the Catarina
1972). For example, Mainelli et al. (2008) all ocean basins, except for the South At- the 1990-2019 climatology (Figure 3a). transition, since the same processes that
demonstrated that the inclusion of OHC in lantic. This deficit in the occurrence of TCs The comparison of its four variables with modulate the development of CT can also
numerical models improved the prediction is generally attributed to an adverse envi- their respective climatologies (Figure 3, first impact extratropical cyclones (Hart, 2003).
of hurricane intensity by up to 20%. In ad- ronment of cold sea surface temperatures column) shows that vorticity, humidity, and As of March 23, both humidity and vor-
dition to improving numerical prediction, and strong vertical wind shear (PEZZA and wind shear were more effective in modu- ticity (i.e., absolute value) remained well
recent studies point to a strong relationship SIMMONDS, 2005). Subtropical cyclones lating the life cycle of the system than po- above the climatology, while wind shear
between the increase in OHC due to global (CSTs), however, routinely occur in the South tential intensity, which in most times it was grew in importance as the system moved
warming and the extreme rainfall of recent Atlantic (e.g., EVANS and BRAUN, 2012; below the climatological level for March. into a region of shear below the theoretical
hurricanes (e.g., TRENBERTH et al., 2018). GOZZO et al., 2014). In other regions such Although counterintuitive, it is not uncom- limit of tropical cyclogenesis of 10 m s-1
Also, according to Trenberth et al. (2018), as the North Atlantic, CSTs undergo Tropical mon for potential intensity to play a sec- proposed by Zehr (1992), remaining in this
OHC values above the climatological aver- Transition (TT) to TCs frequently (EVANS and ondary role in determining GPI (e.g, WANG environment throughout the subsequent
age not only increased the “fuel” available GUISHARD, 2009). Subtropical cyclogenesis and MOON, 2017; GAO et al., 2020). phases of its life cycle (Figure 3m). McTag-
to sustain and intensify Hurricane Harvey, and TT over the South Atlantic only gained During most of the extratropical phase gart-Cowan et al. (2006) showed that a
but also increased flooding from the rains attention after Hurricane Catarina. It start- between 19 and 22 March, the system was more intense and longer duration atypical
associated with it when it hit the mainland. ed as an extratropical cyclone and became under the influence of environments close Rex dipole blocking pattern was responsi-
Another important physical quantity in a CST before transitioning to a proper CT, to climatological wind shear (Figure 3m). In ble for this weak wind shear. On the night
the assessment of tropical cyclogenesis is which hit southern Brazil on March 28, this phase of the storm, the GPI was dom- of March 23, the storm experienced envi-
the potential intensity (EMANUEL and NO- 2004, as a nominal Category 2 hurricane inated by humidity and vorticity. The high ronmental inputs that produced the third
LAN, 2004), which determines the max- (MCTAGGART-COWAN et al., 2006, REBOI- anomalous negative vorticities (Figure 3d) highest peak of GPI (Figure 3a) and the
imum speed that winds associated with TA et al., 2006, REBOITA et al., 2019). are cyclonic (Southern Hemisphere) and subtropical phase of Catarina was reached
tropical cyclones could reach for certain In fact, as the climate changes, the abil- indicate a dynamic factor favorable to cy- a few hours later (MCTAGGART-COWAN
environmental conditions. The ocean sur- ity to predict variations in the frequency of clogenesis (HALL et al., 2001). The vorticity et al., 2006).
face temperature enters as a hot source in TT in the South Atlantic depends on a com-
the thermodynamic term of the equation prehensive view of the factors that modu-
for this variable, with the temperature of lated Catarina. Lauton et al. (2021) applied
the atmospheric tropopause being the cold the existing GPI (EMANUEL and NOLAN,
source. Emanuel (2007) demonstrated that 2004) that quantifies the contribution of
much of the kinetic energy variability at- large-scale environmental factors associat-
tributed to tropical cyclones in the North ed with tropical cyclogenesis to understand
Atlantic and western North Pacific was ex- the life cycle of Catarina. This differs from
plained by potential intensity, in conjunc- previous studies that evaluated each inter-
tion with low-level atmospheric relative dependent factor individually. In addition,
vorticity, humidity, and vertical wind shear. the authors incorporated the analysis of

406 BLUE ECONOMY Ocean and Climate: New Challenges 407