2011–12 South-West Indian Ocean cyclone season
| Season summary map | |
| First storm formed | December 5, 2011 |
|---|---|
| Last storm dissipated | Season currently active |
| Strongest storm | Benilde – 968 hPa (mbar), 150 km/h (90 mph) (10-minute sustained) |
| Total disturbances | 4 |
| Tropical depressions | 4 |
| Total storms | 2 |
| Tropical cyclones | 1 |
| Total fatalities | Unknown |
| Total damage | Unknown |
| South-West Indian Ocean cyclone seasons 2009-10, 2010-11, 2011-12 Post-2011 |
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| Related articles | |
The 2011–12 South-West Indian Ocean cyclone season is an event in the annual cycle of tropical cyclone formation. It began on November 15, 2011, and will end on April 30, 2012, with the exception for Mauritius and the Seychelles, for which it will end on May 15, 2012. These dates conventionally delimit the period of each year when most tropical cyclones form in the region. The basin is defined as the area west of 90°E and south of the Equator in the Indian Ocean, which includes the waters around Madagascar westward to the east coast of Africa. Tropical cyclones in this basin are monitored by the Regional Specialised Meteorological Centre in Réunion.
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Timeline
Storms
Severe Tropical Storm Alenga
| Severe tropical storm (MFR) | |||
|---|---|---|---|
| Tropical storm (SSHS) | |||
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| Duration | December 5 – December 7 (out of basin) | ||
| Intensity | 100 km/h (65 mph) (10-min), 982 mbar (hPa) | ||
On December 5, a rapidly developing area of low pressure crossed 90°E and entered La Réunion's area of responsibility. Within hours of moving into the region, the Joint Typhoon Warning Center (JTWC) classified it as Tropical Cyclone 01S. By this time, a banding eye feature was apparent on satellite imagery. Favorable atmospheric conditions allowed convection to increase in intensity and coverage over its center and good outflow.[1] Several hours later, La Réunion reported that the system had intensified into a Moderate Tropical Storm, with the Mauritus Meteorological service naming it Alenga.[2] Continuing to rapidly intensify, Alenga strengthened into a severe tropical storm later that day.[3] Although predicted to intensify into a tropical cyclone, Alenga weakened near midday December 6 and was downgraded to moderate tropical storm status before it moved out of the SWIO and into the Australian region, early on December 7.[4]
Tropical Depression 02
| Tropical depression (MFR) | |||
|---|---|---|---|
| Tropical storm (SSHS) | |||
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| Duration | December 6 – December 16 | ||
| Intensity | 55 km/h (35 mph) (10-min), 998 mbar (hPa) | ||
On December 6, Météo-France declared a tropical disturbance a tropical depression. On December 7, the cyclone entered an area of strong vertical wind shear causing the low level circulation centre to become exposed. Soon afterwards, Tropical Depression 02 dissipated to a remnant low. But Early on December 8, the system regenerated into a weak tropical depression. Later on December 8, convection redeveloped, and wrapped around the low level center, even as the storm continued moving westward, as it slowly weakened. Late on December 9, Météo-France issued their last advisory on the storm, as it weakened below tropical depression intensity. However, the remnants continued to persist for the next several days. But on December 16, the remnants dissipated completely.
Subtropical Depression 03
| Subtropical depression (SSHS) | |||
|---|---|---|---|
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| Duration | December 19 – December 23 | ||
| Intensity | 55 km/h (35 mph) (10-min), 1000 mbar (hPa) | ||
An area of low pressure located near the southeastern coast of Madagascar, that was previously being tracked by the JTWC as Invest 93S, was designated a subtropical depression by Meteo-France, on December 19.[5] The system did not move much, and persisted through the 20th. However, on December 21, the subtropical depression began to weaken, even as it moved southward, very slowly. Late on December 23, Meteo-France issued their last advisory on the storm, as it dissipated.
Tropical Cyclone Benilde
| Tropical cyclone (MFR) | |||
|---|---|---|---|
| Category 2 tropical cyclone (SSHS) | |||
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| Duration | December 28 (entered basin) – Currently active | ||
| Intensity | 150 km/h (90 mph) (10-min), 968 mbar (hPa) | ||
On December 28, RSMC La Réunion reported that Tropical Disturbance 04 had moved into the region from the Australian region, where it had been monitored for about a week. During that day the disturbance gradually developed further which prompted the JTWC to start issuing advisories on the system and designate it as Tropical Cyclone 04S. On December 29, La Réunion upgraded the system to a moderate tropical storm, which was then named Benilde. Benilde moved in a general westward direction and quickly intensified into a tropical cyclone by December 31. The storm then took turned onto a more southwesterly path as it continued to strengthen. This period of continued strengthening did not last long. On January 1, dry air began to make its way into the southern area of the storm. Convection increased for a short period of time, but later in the day La Réunion noted that Benilde's northern eyewall had collapsed and the system was weakening. On January 3, Benilde weakened into a Severe Tropical Storm. Suffering from severe wind shear, the system continued weakening and it became a tropical depression on January 4.
Storm names
Within the South-west Indian Ocean Tropical Depressions and Subtropical Depressions that are judged to have 10-minute sustained windspeeds of 65 km/h, (40 mph) by the Regional Specialized Meteorological Center on La Réunion Island, France (RSMC La Réunion) are usually assigned a name. However it is the Sub-Regional Tropical Cyclone Advisory Centers in Mauritius and Madagascar who name the systems. The Sub-Regional Tropical Cyclone Advisory Center in Mauritius names the storm should it intensify into a moderate tropical storm between 55°E and 90°E, if the storm should intensify into a moderate tropical storm between 30°E and 55°E then the Sub-Regional Tropical Cyclone Advisory Center in Madagascar assigns the appropriate name to the storm. For the final year, tropical cyclones that move into this region from the Australian region will be renamed by the Sub-Regional Tropical Cyclone Advisory Center in Mauritius, however tropical cyclones moving into the Australian region will not be renamed. New name lists are used every year, whilst a name is normally only used once so thus no names are retired.[6][7]
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Season effects
This table lists all the storms that developed in the Southern Hemisphere during the 2011–2012 South-West Indian Ocean cyclone season. It includes their intensity, duration, name, landfalls, deaths, and damages. All data is taken from Météo-France. The damage figures are all in 2012 USD.
| Storm Name |
Dates active | Storm category at peak intensity |
Peak 10-min sustained winds |
Pressure hPa |
Areas affected | Damage (USD) |
Deaths | Notes |
|---|---|---|---|---|---|---|---|---|
| Alenga | December 5 – December 7 | Severe Tropical Storm | 100 km/h (65 mph) | 982 hPa | None | None | None | |
| 02/02S | December 6 – December 16 | Tropical Depression | 55 km/h (35 mph) | 998 hPa | None | None | None | |
| 03 | December 19 – December 23 | Subtropical Depression | 55 km/h (35 mph) | 1000 hPa | None | None | None | |
| Benilde | December 28 – Active | Tropical cyclone | 150 km/h (90 mph) | 968 hPa | None | None | None | |
| Season Aggregates | ||||||||
| 4 Systems | December 5 – currently active | 150 km/h (90 mph) | 968 hPa | None | None |
See also
- List of Southern Hemisphere cyclone seasons
- Atlantic hurricane seasons: 2011, 2012
- Pacific hurricane seasons: 2011, 2012
- Pacific typhoon seasons: 2011, 2012
- North Indian Ocean cyclone seasons: 2011, 2012
- 2011-12 Australian region cyclone season
- 2011-12 South Pacific cyclone season
References
- ^ "Tropical Cyclone 01S Advisory Number 001". Joint Typhoon Warning Center. United States Navy. December 5, 2011. http://www.webcitation.org/63hml4oX9. Retrieved December 5, 2011.
- ^ "Moderate Tropical Storm Alenga Advisory One". La Réunion. December 5, 2011. http://www.webcitation.org/63hoF9TLl. Retrieved December 5, 2011.
- ^ "Severe Tropical Storm Alenga Advisory Two". La Réunion. December 5, 2011. http://www.webcitation.org/63hoF4ltJ. Retrieved December 5, 2011.
- ^ "Moderate Tropical Storm Alenga Advisory Seven". La Réunion. December 6, 2011. http://www.webcitation.org/63jcxuPmZ. Retrieved December 6, 2011.
- ^ "Subtropical Depression 03 Advisory One". La Réunion. December 19, 2011. http://www.webcitation.org/644hNXkZ4. Retrieved December 21, 2011.
- ^ Regional Association I Tropical Cyclone Committee (2010). "Tropical Cyclone Operational Plan for the South-West Indian Ocean" (PDF). World Meteorological Organization. http://www.wmo.int/pages/prog/www/tcp/documents/TCP-12_2010_English.pdf. Retrieved 2011-07-28.
- ^ Regional Association I Tropical Cyclone Committee (2009). "FAQ: B5) What are the upcoming tropical cyclone names ?". Meteo France. http://www.meteo.fr/temps/domtom/La_Reunion/webcmrs9.0/anglais/faq/FAQ_Ang_B.html. Retrieved 2011-07-05.