Cyclone Anita

Tropical Storm Anita

Tropical storm (SSHS)
Satellite image of the cyclone several hours after being declared tropical
Formed	March 5, 2010
Dissipated	March 11, 2010
Highest winds	1-minute sustained: 75 km/h (45 mph)
Lowest pressure	1000 hPa (mbar)
Fatalities	None reported
Areas affected	Southern Brazil
Part of the 2009-10 South Atlantic cyclone season

Tropical Storm Anita was the second tropical cyclone in the Southern Atlantic Ocean on record, following Cyclone Catarina in March 2004. Originating from an extratropical cyclone over southern Brazil, this system quickly moved offshore, entering a region favoring subtropical development. Above-average sea surface temperatures allowed for sufficient convective development to take place for the storm to be declared a subtropical cyclone by March 8. Gradual organization followed while the storm maintained winds of 65 km/h (40 mph). The system remained roughly 100 to 150 km (62 to 93 mi) off the coast of Brazil as it drifted in a general eastward direction. Early on March 10, the National Oceanic and Atmospheric Administration declared that the storm had transitioned into a tropical cyclone, marking the first fully tropical system in the region since a storm in February 2006. Shortly thereafter, the cyclone attained its peak intensity with winds of 75 km/h (45 mph) and a barometric pressure of 1000 mbar (hPa). The system gradually lost its tropical characteristics and by March 12, the cyclone transitioned into an extratropical system. Around this time, six Brazilian Meteorological services announced that the cyclone would be designated as Tropical Cyclone Anita.

Although a small cyclone, the outer fringes of the storm brought gusty winds to parts of costal Brazil, estimated up to 50 km/h (31 mph) in some places. Heavy rain was also reported in areas further inland, including the city of Porto Alegre. However, the precursor to the cyclone caused more substantial damage. Torrential rainfall and severe weather damaged numerous homes in Rio Grande do Sul. Several tornadoes also touched down between March 5 and 7.^{[citation needed]} Despite the damage, there were no reports of fatalities in relation to the cyclone.

Meteorological history

Storm path

The tropical cyclone was first identified by the Hydrometeorological Prediction Center (HPC), based in the United States, on March 5 over southern Brazil. The system was noted as having the possibility of becoming subtropical as it moved over above average waters.^[1] The next day, the Brazilian meteorological service began issuing summaries on the system as an extratropical cyclone just off the coast of Uruguay. This system quickly tracked northward, moving over southern Brazilian state of Rio Grande do Sul the following day, before moving over the cool waters of the Southern Atlantic Ocean. Sea surface temperatures in the region were above average; however, slightly cooler than late February.^[2] On March 8, the United States Naval Research Laboratory classified the system as an area of interest, designating it as 90Q.^[3]

Satellite image of the cyclone while subtropical on March 9, 2010

Later on March 8, the National Hurricane Center, based in Miami, Florida, classified the system as Low 90SL.^[4] By this time, the cyclone was estimated to have winds between 65 and 100 km/h (40 and 65 mph) and featured a strong, onshore flow. Deep convection developed around the center of circulation in response to favorable atmospheric conditions. Additionally, satellites monitoring the storm determined that the cyclone was developing a warm core, a feature of tropical cyclones and was being enhanced by a trough to the west.^[5] By March 9, the Brazilian Meteorological service classified the low as a subtropical cyclone, the first such storm since an unnamed cyclone in January 2009.^[2]

Cells of deep convection persisted around the system throughout the day, indicating that it was acquiring more tropical characteristics. Sustained winds at this time were estimated at 65 km/h (40 mph), equivalent to a minimal tropical storm. It was stated by the HPC that if wind shear in the region subsided, there was a possibility of the cyclone becoming fully tropical.^[6] Radar imagery from nearby meteorological stations indicated that the storm could be developing an eyewall as it drifted offshore. A scatterometer image later on March 9 confirmed that the system had developed a closed, low-level circulation. In response to this data, the Brazilian Meteorological service stated that the subtropical system had transitioned into a tropical cyclone.^[2]

By March 10, the cyclone began moving away from the Brazilian coastline and continued to become better defined. During the morning hours, the National Oceanic and Atmospheric Administration officially classified the cyclone as being tropical through the Dvorak technique.^[2] Later that day, the system attained its peak intensity with winds of 75 km/h (45 mph) and a barometric pressure of 1000 mbar (hPa).^[4] On March 12, the Brazilian Meteorological service announced that the system would be classified with the name Anita,^[2] after Anita Garibaldi, a historic figure of the states of Rio Grande do Sul and Santa Catarina, both affected by the storm.^[7]

Impact, classification, and records

In Rio Grande do Sul, officials warned residents of the possibility of heavy rains and strong winds, gusting up to 150 km/h (90 mph) at times. Boaters were advised not to venture out into the storm as swells produced by the system were estimated at 3 to 5 m (9.8 to 16 ft).^[8]

Brazilian meteorologists stated that the formation of this storm and its transition into a tropical cyclone could be regarded as "historic". Tropical cyclone formation in the Atlantic Ocean south of the equator is extremely rare, with only eight other documented cyclones forming in this region in history. Although a minor system, it marked the first time that a tropical or subtropical system formed in consecutive years, following a subtropical storm in January 2009.^[9] Upon being declared subtropical by the HPC on March 8, the tropical cyclone became the first system in the southern Atlantic to be identified using the new suffix; SL, for the region.^[3][4] On March 12, the system was designated as Anita.^[2]

See also

Tropical cyclones portal

• Cyclone Catarina
• Subtropical Storm Arani
• 2009–10 Southern Hemisphere tropical cyclone season (disambiguation)
• 2010 Atlantic hurricane season
• South Atlantic tropical cyclone
• List of tropical cyclones

References

1. ^ Flores, Llanque and Davidson (March 5, 2010). "South American Model Discussion March 5, 2010". Hydrometeorological Prediction Center. http://www.webcitation.org/5o19iNZ9A. Retrieved March 10, 2010. 
2. ^ ^{a b c d e f} (Portuguese) "Monitoramento - Ciclone tropical na costa gaúcha". Brazilian Meteorological Service. March 2010. http://www.webcitation.org/5o7aEbpqG. 
3. ^ ^{a b} "Invest 90Q Running Best Track". United States Naval Research Laboratory. March 2010. http://www.webcitation.org/5o8JfzRLL. Retrieved March 10, 2010. 
4. ^ ^{a b c} "Low 90SL Running Best Track". National Hurricane Center. March 2010. http://www.webcitation.org/5o7vpcHL5. Retrieved March 10, 2010. 
5. ^ Flores, Llanque and Davidson (March 8, 2010). "South American Model Discussion March 8, 2010". Hydrometeorological Prediction Center. http://www.webcitation.org/5o5TANpBv. Retrieved March 10, 2010. 
6. ^ Flores, Llanque and Davidson (March 9, 2010). "South American Model Discussion March 9, 2010". Hydrometeorological Prediction Center. http://www.webcitation.org/5o6UOtu2z. Retrieved March 10, 2010. 
7. ^ Hackbart, Eugenio (March 12, 2010). "Rare South Atlantic Tropical Storm Designated Anita". MetSul Meteorologia. http://metsul.com/blog/?cod_blog=1&cod_publicacao=134. Retrieved 2010-05-31. 
8. ^ (Portuguese) MetSul Meteorologia (March 7, 2010). "Previsão de ciclone deixa região Sul em alerta nesta segunda". Correio do Povo. http://www.correiodopovo.com.br/Noticias/?Noticia=108476. Retrieved March 10, 2010. 
9. ^ (Portuguese) MetSul Meteorologia (March 9, 2010). "Ciclone está mais próximo do Litoral Norte". Correio do Povo. http://www.correiodopovo.com.br/Noticias/?Noticia=109446. Retrieved March 10, 2010. 

External links

• Brazilian Meteorological service weather blog (Portuguese)