Australian East-Coast Cyclones. Part I: Synoptic Overview and Case Study (original) (raw)
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Analysis of Hurricane Catarina (2004)
Monthly Weather Review, 2006
The development of Hurricane Catarina over the western South Atlantic Ocean in March 2004 marks the first time that the existence of a hurricane has been confirmed by analysis and satellite imagery in the South Atlantic basin. The storm undergoes a complex life cycle, beginning as an extratropical precursor that moves east-southeastward off the Brazilian coast and toward the midlatitudes. Its eastward progress is halted and the system is steered back westward toward the Brazilian coast as it encounters a strengthening dipole-blocking structure east of the South American continent. Entering the large region of weak vertical shear that characterizes this blocking pattern, Catarina begins a tropical transition process over anomalously cool 25°C ocean waters above which an elevated potential intensity is supported by the cold upper-level air associated with the trough component of the block. As the convective outflow from the developing tropical system reinforces the ridge component of the dipole block, the storm is accelerated westward toward the Santa Catarina province of Brazil and makes landfall there as a nominal category-1 hurricane, causing extensive damage with its heavy rains and strong winds.
New perspectives on the synoptic and mesoscale structure of Hurricane Catarina
Atmospheric Research, 2010
This work explores in detail synoptic and mesoscale features of Hurricane Catarina during its life cycle from a decaying baroclinic wave to a tropical depression that underwent tropical transition (TT) and finally to a Category 2 hurricane at landfall over Santa Catarina State coast, southern Brazil. This unique system caused 11 deaths mostly off the Brazilian coast and an estimated half billion dollars in damage in a matter of a few hours on 28 March 2004. Although the closest meteorological station available was tens of kilometres away from the eye, in situ meteorological measurements provided by a work-team sent to the area where the eye made landfall unequivocally reproduces the tropical signature with category 2 strength, adding to previous analysis where this data was not available. Further analyses are based mostly on remote sensing data available at the time of the event. A classic dipole blocking set synoptic conditions for Hurricane Catarina to develop, dynamically contributing to the low wind shear observed. On the other hand, on its westward transit, large scale subsidence limited its strength and vertical development. Catarina had relatively cool SST conditions, but this was mitigated by favourable air-sea fluxes leading to latent heat release-driven processes during the mature phase. The ocean's dynamic topography also suggested the presence of nearby warm core rings which may have facilitated the transition and post-transition intensification. Since there were no records of such a system at least in the past 30 years and given that SSTs were generally below 26°C and vertical shear was usually strong, despite all satellite data available, the system was initially classified as an extratropical cyclone. Here we hypothesise that this categorization was based on inadequate regional scale model outputs which did not account for the importance of the latent heat fluxes over the ocean. Hurricane Catarina represents a dramatic event on weather systems in South America. It has attracted attention worldwide and poses questions as whether or not it is a symptom of global warming. Atmospheric Research 95 (2010) 157-171 ⁎ Corresponding author. Rua do Matão,
Large-scale Factors in Tropical and Extratropical Cyclone Transition and Extreme Weather Events
Annals of the New York Academy of Sciences, 2008
Transition mechanisms characterizing changes from hurricanes to midlatitude cyclones and vice-versa (extratropical and tropical transition) have become a topic of increasing interest, partially because of their association with recent unusual storms that have developed in different ocean basins of both hemispheres. The aim of this work is to discuss some recent cases of transition and highly unusual hurricane developments and to address some of their wider implications for climate science. Frequently those dramatic cyclones are responsible for severe weather, potentially causing significant damage to property and infrastructure. An additional manifestation discussed here is their association with cold surges, a topic that has been very little explored in the literature. In the Southern Hemisphere, the first South Atlantic hurricane, Catarina,
International Journal of Climatology, 2009
The landfall of Cyclone Catarina on the Brazilian coast in March 2004 became known as the first documented hurricane in the South Atlantic Ocean, promoting a new view on how large-scale features can contribute to tropical transition. The aim of this paper is to put the large-scale circulation associated with Catarina's transition in climate perspective. This is discussed in the light of a robust pattern of spatial correlations between thermodynamic and dynamic variables of importance for hurricane formation. A discussion on how transition mechanisms respond to the present-day circulation is presented. These associations help in understanding why Catarina was formed in a region previously thought to be hurricane-free.
A climatology of Southern Hemisphere extratropical cyclones
Climate Dynamics, 1993
A climatology of extratropical cyclones determined by an objective automatic scheme applied to 15 years (1975-89) of once-daily Australian Bureau of Meteorology hemispheric analyses is presented. Contour maps of the positions of formation (cyclogenesis), dissipation (cyclolysis) together with other cyclone statistics are presented. The distribution of cyclones through the hemisphere was found to be dominated by a permanent high latitude core coincident with the circumpolar trough. During the winter and intermediate seasons, two mid latitude branches are evident in the cyclone density originating in the Tasman Sea and South American sectors, both spiraling, poleward and merging with the circumpolar core in the Southern Oceans. Systems were observed to move in an eastsouth-east direction, away from their location of formation, exhibiting peak speeds of migration in the mid latitudes. Little seasonality was evident in the densitiy distribution of cyclones through the Southern Oceans, but a considerable amount was found in their central pressure.
A comparative study of intense surface cyclones off the coasts of southeastern Brazil and Mozambique
International Journal of Climatology, 2019
An analysis of two groups of near surface intense cyclonic vortices, one off the southeastern Brazil coast and the other off the Mozambique coast, in the period 1979-2012 is undertaken for comparison of their characteristics with the help of the TRACK algorithm and the NCEP2 Reanalysis datasets. The aim is to understand the nature of intense cyclogeneses in those two subtropical coastal regions. Although the two groups form in almost the same latitude belt and under similar conditions and thus have some common features, they differ in several evolution and movement characteristics. The South American intense cyclones are more frequent. They move rapidly into southern South Atlantic while the African cyclones remain quasi-stationary during the first two days of their life time. Thermal structures show that the Mozambique Channel region presents more conditional instability. The South American intense cyclones present more kinetic energy than their counterparts in the first two days. The precipitation around the South American cyclones decreases gradually. The Mozambique Channel cyclones gain kinetic energy after moving away from the Madagascar Island and preserve their baroclinity longer and therefore the mean precipitation rate around their centers remains constant. The sea surface temperature, the geographical features and the circulation characteristics of the two regions are responsible for the differences. Eventually, after four days of their formation, cyclones of both the groups join the Southern Hemispheric extratropical storm-tracks.
Simulations of the Transformation Stage of the Extratropical Transition of Tropical Cyclones
Monthly Weather Review, 2001
The physical mechanisms associated with the transformation stage of the extratropical transition of a tropical cyclone are simulated with a mesoscale model using initial environmental conditions that approximate the mean circulations defined by Klein et al. The tropical cyclone structural changes simulated by the U.S. Navy Coupled Ocean-Atmosphere Model Prediction System mesoscale model during the three steps of transformation compare well with available observations. During step 1 of transformation when the tropical cyclone is just beginning to interact with the midlatitude baroclinic zone, the main environmental factor that affects the tropical cyclone structure appears to be the decreased sea surface temperature. The movement of the tropical cyclone over the lower sea surface temperatures results in reduced surface heat and moisture fluxes, which weakens the core convection and the intensity decreases. During step 2 of transformation, the low-level temperature gradient and vertical wind shear associated with the baroclinic zone begin to affect the tropical cyclone. Main structural changes include the development of cloud-free regions on the west side of the tropical cyclone, and an enhanced ''delta'' rain region to the northwest of the tropical cyclone center. Gradual erosion of the clouds and deep convection in the west through south sectors of the tropical cyclone appear to be from mechanically forced subsidence due to the convergence between the midlatitude flow and the tropical cyclone circulation. Whereas the warm core aloft is advected downstream, the mid-to low-level warm core is enhanced by subsidence into the tropical cyclone center, which implies that the low-level cyclonic circulation may continue to be maintained.
Relating winds along the Southern Brazilian coast to extratropical cyclones
Meteorological Applications, 2011
Intense wind events at the southern Brazilian coast cause severe socio-economic losses. Generally, such events have been associated with extratropical cyclones over the Southwest Atlantic Ocean. The purpose of this study is to identify favoured locations and the processes through which the winds are associated with the extratropical cyclones. Using a statistical analysis, the wind speed observed at nine meteorological stations was compared with cyclone depth and offshore distance. Both cyclone depth and location were obtained through an objective procedure of identifying and tracking. Generally, the winds are well associated with the extratropical cyclones only south of 28°S. Altitude also plays an important role in this relationship. Furthermore, the cyclones influence the observed wind field up to 1200 km inland at higher latitude locations. For stations near 28°S, cyclones further from the coast have an influence, but with smaller statistical significance.