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2009–10 South-West Indian Ocean cyclone season


2009–10 South-West Indian Ocean cyclone season

2009–10 South-West Indian Ocean cyclone season
Season summary map
First system formed August 18, 2009 (01)
Last system dissipated May 29, 2010 (Joel)
Strongest storm Edzani – 910 hPa (mbar), 220 km/h (140 mph) (10-minute sustained)
Total disturbances 16
Total depressions 12
Total storms 10
Tropical cyclones 5
Intense tropical cyclones 2
Total fatalities 40
Total damage Unknown
South-West Indian Ocean tropical cyclone seasons
2007–08, 2008–09, 2009–10, 2010–11, 2011-12
Related articles

The 2009–10 South-West Indian Ocean tropical cyclone year officially started on July 1, 2009, and ended on June 30, 2010, after incorporating the tropical cyclone season which ran from November 1 to April 30 for all areas except for Mauritius and the Seychelles, for which it ended on May 15, 2010. In this basin which officially runs from 30 to 90E and is to the south of the equator, the main warning center is the Regional Specialized Meteorological Center on La Reunion Island; however they delegate the naming of Cyclones to the Meteorological services of Mauritius and Madagascar.[1]

It was predicted by the Mauritius Meteorological service that there would be between nine and eleven named storms in the South West Indian Ocean during the season.[2] Their further assessment that there was a good probability of a named storm forming in November was justified when Tropical Cyclone Anja formed on November 14.


Tropical Disturbance 01

Tropical disturbance (MFR)
Duration August 18 – August 20
Peak intensity 35 km/h (25 mph) (10-min)  1004 mbar (hPa)

Early on August 17, the JTWC reported that an area of disturbed weather had formed about 1200 kilometres, (750 miles), to the east of Diego Garcia.[3] The convection had a developed low level circulation center, however convection had not started to consolidate around it and was in an area of strong vertical wind shear. During that day the disturbance gradually developed further as the environment around it gradually improved and was designated as Tropical Disturbance 01 by RSMC La Reunion early the next day.[4][5] However later that day they downgraded it to a zone of disturbed weather and released their final advisory on the disturbance as it had remained weak with the low level circulation center remaining weak and exposed.[6] Over the next few days it weakened further before dissipating on August 20.[7]

Zone of Disturbed Weather 02

Zone of Disturbed Weather (MFR)
Duration September 18 – September 20
Peak intensity 35 km/h (25 mph) (10-min)  1008 mbar (hPa)

During September 17, both TCWC Jakarta and the JTWC reported that an area of convection had persisted about 740 km (460 mi), to the south east of Sumatra in Indonesia.[8][9] Satellite imagery was showing that the convection was slowly starting to consolidate with a well defined low level circulation centre off the western coast of Sumatra.[9] However it was not expected to develop any further due to being in area of high vertical wind shear in excess of 40 knots (74 km/h).[9] Despite this it was designated as a tropical low early the next day by TCWC Perth.[10] The JTWC then declared early the next day that the disturbance had dissipated as it crossed 90E and moved into RSMC La Reunion's area of responsibility.[11][12] TCWC Perth continued to monitor the tropical low as it slowly developed further until early on September 20 when RSMC La Reunion designated it as the second Zone of Disturbed Weather of the 2009–10 as convection had developed over the system and the amount of vertical wind shear over the system had dropped.[13][14] However they released their final advisory later that day as convection had dissipated in the northern quadrants of the system.[15]

Tropical Disturbance 03

Tropical disturbance (MFR)
Duration November 7 – November 10
Peak intensity 45 km/h (30 mph) (10-min)  1002 mbar (hPa)
Early on November 7, the JTWC issued a Tropical Cyclone Formation Alert on a system north of Diego Garcia. Later that day, RSMC La Reunion upgraded the system to a tropical disturbance. Despite forecasts that the system would strengthen to a depression, it was substantially affected by shear, and as a result, the JTWC cancelled their TCFA on November 9.

Tropical Cyclone Anja

Tropical cyclone (MFR)
Category 3 tropical cyclone (SSHWS)
Duration November 13 – November 18
Peak intensity 155 km/h (100 mph) (10-min)  950 mbar (hPa)

RSMC La Reunion commenced advisories on Tropical Disturbance 04 on November 14, raising the status to a Tropical Depression later the same day. At the time of formation, it was some 390 mi (630 km) south of Diego Garcia. Throughout that day, and into the 15th, Anja rapidly intensified from a severe tropical storm to a tropical cyclone on the MFR scale and a Category 3-equivalent cyclone on the Saffir-Simpson Hurricane Scale (SSHS), while remaining well away from land. The system displayed annular characteristics and was very small; its diameter was 60 nautical miles (110 km) and it displayed a pinhole eye.[16] The storm peaked at a Category 3-equivalent intensity and held its strength until November 17 when the storm rapidly weakened to a tropical storm. Final advisories were issued on November 18 as the system weakened to a depression and became extratropical.

Moderate Tropical Storm Bongani

Moderate tropical storm (MFR)
Tropical storm (SSHWS)
Duration November 22 – November 25
Peak intensity 75 km/h (45 mph) (10-min)  996 mbar (hPa)

On November 22, RSMC La Reunion commenced issuing advisories for Tropical Disturbance 05 about 500 mi (800 km) northeast of Madagascar. The next day it strengthened to a Moderate Tropical Storm and was named 'Bongani'. On November 23–24, the system remained small sized and was undergoing a temporarily southeasterly constraint. According to CIMSS data (MIMIC-TPW), the dry air that was to the southwest of the system interfered with circulation of the system and temporarily limited the intensification rate. On the morning of November 24, Bongani rapidly weakened into a tropical disturbance.

The remnants of Bongani brought unsettled weather to the Mayotte Islands. Moderate rains affected the region between November 26 and 27; waves associated with the storm also averaged 3 m (9.8 ft) along coastal areas with some reaching 6 m (20 ft).[17] In the nearby Comoros Islands, waves were similarly high, with the highest reaching 5 m (16 ft).[18]

Intense Tropical Cyclone Cleo

Intense tropical cyclone (MFR)
Category 4 tropical cyclone (SSHWS)
Duration December 6 – December 14
Peak intensity 195 km/h (120 mph) (10-min)  930 mbar (hPa)

On December 6, a strong tropical disturbance 06 newly formed in the central Indian Ocean. The storm was expected to strengthen slowly, however, the next day, the disturbance strengthened into a severe tropical storm while being given a designation as Tropical Cyclone 03S by the JTWC. On 8 December it strengthened rapidly to become the first Intense Tropical Cyclone of the season and a Category 4-equivalent cyclone on the Saffir-Simpson Hurricane Scale (SSHS). It sustained this strength for a day peaked at a Category 4-equivalent intensity and held its strength as a high strong category 4-equivalent, then on the 10th slowly weakened to a category 2 equivalent cyclone. The weakening continued steadily, and the final advisory was issued on December 12 when the remnants were 370 miles (600 km) north of Rodrigues. Later that day, the remnants of Ex-Cleo regenerated to a tropical depression, but it weakened to a tropical disturbance and dissipated on December 14.

Moderate Tropical Storm David

Moderate tropical storm (MFR)
Tropical storm (SSHWS)
Duration December 12 – December 25
Peak intensity 85 km/h (50 mph) (10-min)  987 mbar (hPa)

On December 12, a zone of disturbed weather formed in the Southern Indian Ocean near the border with the Australian sector. The next day the RSMC classified it as Tropical Disturbance 07, and JTWC as Tropical Cyclone 05S, but its movement to cooler water and higher levels of wind shear weakened the tropical system on the 14th. The remnants continued to show a Low level Circulation Centre accompanied by flaring convection as they headed west or northwest, and the organisation began to improve again on the 19th. [19] It continued to organize throughout the next day, and by the 21st of December it was named Moderate Tropical Storm David by the Mauritius Meteorological Service.[20] It then reversed its direction of motion and headed east-southeast while strengthening to a Severe Tropical Storm.[21] Its strength fluctuated for the next few days, and by Christmas Day it was moving very little and windshear weakened it to a Tropical Disturbance. The final advisory from the RSMC was issued on December 25, although the remnant continued to produce bursts of poorly organized convection for several days as it reversed direction again and headed west.

In post-season analysis, David was downgraded to a Moderate Tropical Storm as winds were reassessed to have never exceeded 85 km/h (50 mph).

On December 29, the remnants of David brought heavy rain to the islands of Mauritius and Réunion. Most of Mauritius recorded over 100 mm (3.9 in) of rain within a 24-hour span, with a maximum of 146.2 mm (5.76 in) in Mon Loisir Rouillard. Widespread flash flooding took place across the island, resulting in over 20 calls to firefighters for rescue. Officials deployed special mobile forces in several cities due to the risk of increased flooding.[22]

Very Intense Tropical Cyclone Edzani

Very intense tropical cyclone (MFR)
Category 5 tropical cyclone (SSHWS)
Duration January 4 (Entered basin) – January 14
Peak intensity 220 km/h (140 mph) (10-min)  910 mbar (hPa)

Tropical Low 03U of the Australian Region crossed the 90ºE meridian on 4 January and was designated Tropical Disturbance 8 by RSMC La Réunion. The system showed two low-level circulation centres for a while, but on 5 January these consolidated, and the combination was upgraded to a Tropical Depression. At 0300 UTC on January 6, the JTWC starts issuing advisories designating the system as 07S, and shortly thereafter the RSMC upgraded it to Moderate Tropical Storm Edzani. Early on January 7, RSMC La Reunion upgraded Edzani to a Severe Tropical Storm, and it strengthened rapidly throughout the day to become an Intense Tropical Cyclone. The next day it became a Very Intense Tropical Cyclone and category 5 by JTWC, the first since Juliet in April 2005. On January 9, Edzani was downgraded to an Intense Tropical Cyclone due to decreasing sea surface temperatures. It continued to weaken during the day, as sea surface temperatures continued to decrease. By January 10, it was only a Tropical Cyclone, and within the next few days it weakened to Moderate Tropical Storm strength. The RSMC classified it as a subtropical cyclone by January 12, although JTWC treated it as tropical for 2 days longer.

Tropical Disturbance 09

Tropical disturbance (MFR)
Duration January 15 – January 16
Peak intensity 45 km/h (30 mph) (10-min)  1005 mbar (hPa)

An area of disturbed weather, first observed over the Mozambique Channel around 8 January, moved across northern Madagascar and into the Indian Ocean where it displayed occasional bursts of convection. On 15 January the LLCC improved in organisation, and the RSMC designated it as a Tropical Disturbance 245 nmi (454 km) to the west-southwest of La Réunion. The next day, RSMC La Reunion issued their final advisory on the system as the center was ill-defined.

Subtropical Depression 10

Subtropical depression (MFR)
Tropical storm (SSHWS)
Duration January 25 – January 31
Peak intensity 65 km/h (40 mph) (10-min)  995 mbar (hPa)

On January 26, RSMC La Réunion announced that a Zone of Disturbed Weather had formed about 350 miles (560 km) NNE of Mauritius. Next day this was raised to a Tropical Disturbance, and JTWC designated is as Tropical Cyclone 11S based on 1-minute wind strength. By January 29 it displayed hybrid characteristics and was classified as a subtropical depression, although the maximum winds reached storm strength.

Moderate Tropical Storm Fami

Moderate tropical storm (MFR)
Tropical storm (SSHWS)
Duration February 1 – February 3
Peak intensity 85 km/h (50 mph) (10-min)  990 mbar (hPa)

On February 1, RSMC La Reunion commenced issuing advisories for Tropical Disturbance 11 in the Mozambique Channel. On February 2 it strengthened to a Moderate Tropical Storm and was named Fami. Shortly after this it made landfall on the western Malagasy coast and weakened rapidly to a depression. Fami dissipated on February 2.

Intense Tropical Cyclone Gelane

Intense tropical cyclone (MFR)
Category 4 tropical cyclone (SSHWS)
Duration February 15 – February 22
Peak intensity 205 km/h (125 mph) (10-min)  930 mbar (hPa)

On February 15, the RSMC announced the formation of Tropical Disturbance 12 approximately 650 nmi (1,200 km) NNE of La Réunion. Hours later it was classified as Moderate Tropical Storm Gelane. It reached Tropical Cyclone strength briefly on February 17, but quickly weakened to a Severe Tropical Storm. Then on February 18, it restrengthened back into a Tropical Cyclone, eventually becoming an Intense Tropical Cyclone. It remained a small system and weakened rapidly as wind shear effects increased.

Severe Tropical Storm Hubert

Severe tropical storm (MFR)
Tropical storm (SSHWS)
Duration March 7 – March 15
Peak intensity 100 km/h (65 mph) (10-min)  985 mbar (hPa)

On March 9, a tropical disturbance formed between Madagascar and Réunion. On March 10 it strengthened to a tropical storm and was named Hubert by the meteorological service of Madagascar. It strengthened to a severe tropical storm as it approached the Madagascar coast, and made landfall north of Mananjary. At least ten people were killed by the storm and 32,000 others were affected throughout Madagascar.[23] Later reports confirmed that four other people had been killed and two more were missing. Nearly 38,000 people were left homeless by flooding triggered by torrential rains from the storm.[24]

Tropical Cyclone Imani

Tropical cyclone (MFR)
Category 1 tropical cyclone (SSHWS)
Duration March 20 – March 28
Peak intensity 130 km/h (80 mph) (10-min)  965 mbar (hPa)

Tropical Disturbance 14 formed on 22 March in the far east of the SW Indian Ocean basin, close to 90ºE. Although the precursor disturbance had been drifting eastwards, TD 14 was predicted to remain in this basin and not move into the Australian. It became a tropical depression later the same day, and was upgraded to Moderate Tropical Storm Imani on 23 March and a Severe Tropical Storm the next day. It continued to strengthen as it moved southwards, and reached tropical cyclone strength on 25 March. It started to dissipate on March 26, and La Reunion had stopped releasing advisories on Imani at 1200z, March 26.

Tropical Depression 15 (Robyn)

Tropical depression (MFR)
Tropical depression (SSHWS)
Duration April 7 – April 7
Peak intensity 55 km/h (35 mph) (10-min)  1002 mbar (hPa)

The remnants of Cyclone Robyn crossed into this basin on 7 April as a Filling Depression, and a single advisory was issued by RSMC La Réunion.

Subtropical Storm Joel

Subtropical storm (MFR)
Subtropical depression (SSHWS)
Duration May 26 – May 29
Peak intensity 110 km/h (70 mph) (10-min)  990 mbar (hPa)

An area of convection southwest of Madagascar was designated Subtropical Depression 16 by RSMC La Reunion on 26 May. The small system strengthened rapidly and was soon named Joel, although still classified as a Subtropical Depression. NASA also considered the storm to have been subtropical, attaining peak one-minute sustained winds of 85 km/h (50 mph).[25]

In post-season analysis, Joel was discovered to have briefly been a tropical storm before transitioning into a subtropical cyclone.

Storm Names

Tropical disturbances are named upon reaching moderate tropical storm strength.[26] If a tropical disturbance reaches this intensity west of 55°E, then the Sub-Regional Tropical Cyclone Advisory Centre in Madagascar assigns the appropriate name to the storm. If it reaches moderate tropical storm strength between 55°E and 90°E, then the Sub-Regional Tropical Cyclone Advisory Centre in Mauritius names the storm.[26] A new list of names is drawn up and used each year, so no names are retired.[26] The names for this season are as follows:[27]

  • Anja
  • Bongani
  • Cleo
  • David
  • Edzani
  • Fami
  • Gelane
  • Hubert
  • Imani
  • Joel
  • Kanja (unused)
  • Lunda (unused)
  • Mohono (unused)
  • Nigel (unused)
  • Olympe (unused)
  • Pamela (unused)
  • Quentin (unused)
  • Rahim (unused)
  • Savana (unused)
  • Themba (unused)
  • Uyapo (unused)
  • Viviane (unused)
  • Walter (unused)
  • Xangy (unused)
  • Yemurai (unused)
  • Zanele (unused)

Season effects

This table lists all the storms that developed in the Southern Hemisphere during the 2009–2010 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 from 2009 USD.

Name Dates active Peak classification Sustained
Pressure Land areas affected Damage
Deaths Refs
01 August 18 Tropical Disturbance 35 km/h (20 mph) 1004 hPa (29.65 inHg) None None None
02 September 18 – 20 Zone of Disturbed Weather 35 km/h (20 mph) 1008 hPa (29.77 inHg) None None None
03 September 18 – 20 Tropical Disturbance 45 km/h (30 mph) 1002 hPa (29.59 inHg) None None None
Anja November 14 – 18 Tropical Cyclone 155 km/h (100 mph) 950 hPa (28.05 inHg) None None None
Bongani November 22 – 25 Moderate Tropical Storm 75 km/h (45 mph) 997 hPa (29.44 inHg) Madagascar
Cleo December 6 – 14 Intense Tropical Cyclone 195 km/h (120 mph) 925 hPa (27.32 inHg) None None None
David December 12 – 25 Moderate Tropical Storm 85 km/h (50 mph) 987 hPa (29.14 inHg) Reunion, Mauritius, Madagascar
Edzani January 4 – 14 Very Intense Tropical Cyclone 220 km/h (140 mph) 910 hPa (26.87 inHg) None None None
09 January 15 Tropical Disturbance 45 km/h (30 mph) 1005 hPa (29.68 inHg) Reunion, Mauritius, Madagascar
10/11S January 26 – 30 Subtropical Depression 65 km/h (40 mph) 1005 hPa (29.68 inHg) Reunion, Mauritius, Madagascar
Fami February 1 – 3 Moderate Tropical Storm 85 km/h (50 mph) 994 hPa (29.35 inHg) Madagascar
Gelane February 15 – 22 Intense Tropical Cyclone 205 km/h (125 mph) 930 hPa (27.46 inHg) Reunion, Mauritius, Rodrigues, Madagascar
Hubert March 7 – 15 Moderate Tropical Storm 100 km/h (65 mph) 985 hPa (29.08 inHg) Madagascar
Imani March 20 – 27 Tropical Cyclone 130 km/h (80 mph) 965 hPa (28.50 inHg) None None None
Robyn April 7 Tropical Depression 55 km/h (35 mph) 998 hPa (29.47 inHg) None None None
Joel May 22 – 29 Subtropical storm 110 km/h (70 mph) 990 hPa (29.23 inHg) Madagascar
Season Aggregates
16 systems August 18 – May 29   220 km/h (140 mph) 910 hPa (26.87 inHg)  

See also


  1. ^ "Tropical Cyclone Operational Plan for the South West Indian Ocean (2006)".  
  2. ^ "The 2009 – 2010 Summer Season Outlook".  
  3. ^ "Signifiicant Tropical Weather Advisory for the Indian Ocean 2009-08-17 11z".  
  4. ^ "Signifiicant Tropical Weather Advisory for the Indian Ocean 2009-08-18 18z".  
  5. ^ "RSMC Tropical Cyclone Bulletin 2009-08-18 00z".  
  6. ^ "RSMC Technical Bulletin 2009-08-18 12z".  
  7. ^ "Signifiicant Tropical Weather Advisory for the Indian Ocean 2009-08-20 18z".  
  8. ^ "Tropical Weather Outlook: 2009-09-16 06z" (in Bahasa Indonesia).  
  9. ^ a b c "Significant Tropical Weather Advisory for the Indian Ocean 2009-09-16 11z".  
  10. ^ "TCWC Perth Tropical Cyclone Outlook for the Central Indian Ocean 2009-09-17 0400z".  
  11. ^ "Significant Tropical Weather Advisory for the Indian Ocean 2009-09-18 11z".  
  12. ^ "Operational Best Track Details for 91S Invest".  
  13. ^ "Tropical Cyclone Outlook for the Central Indian Ocean".  
  14. ^ "RSMC La Reunion Tropical Cyclone Warning 2009-09-20 06z".  
  15. ^ "RSMC La Reunion Tropical Cyclone Warning 2009-09-20 12z".  
  16. ^ "JTWC Warning 07 for Tropical Cyclone 01S (Anja)".  
  17. ^ Staff Writer (November 26, 2009). "Bongani apporte la pluie" (in Français). Mayotte Hebdo. Retrieved December 9, 2009. 
  18. ^ Hakim Ahamed Zoubeiri (November 26, 2009). "Ex-Bongani : pluie, orage et houle sur les Comores" (in Français). Actualité des Iles Comoros. Retrieved December 19, 2009. 
  19. ^ "Significant Tropical Weather Advisory for the Indian Ocean".  
  20. ^ "Moderate Tropical Storm 7 (David) Warning 09".  
  21. ^ "Severe Tropical Storm 14 (David) Warning 14".  
  22. ^ Julien Tuyau (December 29, 2009). "Pluies diluviennes: les pompiers et la Special Mobile Force en état d'alerte" (in Français). La Sentinelle. Retrieved December 29, 2009. 
  23. ^
  24. ^
  25. ^
  26. ^ a b c "Tropical cyclone Operational Plan for the Southwest Indian Ocean".  
  27. ^ "Tropical Cyclone Names 2009–10". 2009-08-13. Retrieved 2009-08-18. 

External links

  • Joint Typhoon Warning Center (JTWC).
  • Météo France (RSMC La Réunion).
  • World Meteorological Organization
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