2009–10 South-West Indian Ocean cyclone season
The 2009–10 South-West Indian Ocean tropical cyclone season was a near average event in tropical cyclone formation. The season 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 Réunion Island ; however they delegate the naming of Cyclones to the Meteorological services of Mauritius and Madagascar.
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. 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.
Timeline
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from:18/08/2009 till:20/08/2009 color:ZD text:"01 "
from:18/09/2009 till:20/09/2009 color:ZD text:"02 "
from:07/11/2009 till:10/11/2009 color:ZD text:"03 "
from:13/11/2009 till:18/11/2009 color:IT text:"Anja "
from:20/11/2009 till:25/11/2009 color:TS text:"Bongani "
from:03/12/2009 till:14/12/2009 color:IT text:"Cleo "
from:12/12/2009 till:26/12/2009 color:ST text:"David "
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from:04/01/2010 till:14/01/2010 color:VI text:"Edzani "
from:15/01/2010 till:16/01/2010 color:ZD text:"09 "
from:25/01/2010 till:31/01/2010 color:TD text:"10 "
from:01/02/2010 till:03/02/2010 color:TS text:"Fami "
from:15/02/2010 till:21/02/2010 color:IT text:"Gelane "
from:09/03/2010 till:11/03/2010 color:ST text:"Hubert "
from:22/03/2010 till:26/03/2010 color:TC text:"Imani "
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from:07/04/2010 till:07/04/2010 color:TD text:"Robyn "
from:26/05/2010 till:29/05/2010 color:TD text:"Joël "
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from:01/08/2009 till:01/09/2009 text:August
from:01/09/2009 till:01/10/2009 text:September
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from:01/11/2009 till:01/12/2009 text:November
from:01/12/2009 till:01/01/2010 text:December
from:01/01/2010 till:01/02/2010 text:January
from:01/02/2010 till:01/03/2010 text:February
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Systems
Tropical Disturbance 01
Early on August 17, the JTWC reported that an area of disturbed weather had formed about 1200 kilometres,, to the east of Diego Garcia. 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 Réunion early the next day. 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. Over the next few days it weakened further before dissipating on August 20.Zone of Disturbed Weather 02
During September 17, both TCWC Jakarta and the JTWC reported that an area of convection had persisted about, to the south east of Sumatra in Indonesia. 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. However it was not expected to develop any further due to being in area of high vertical wind shear in excess of. Despite this it was designated as a tropical low early the next day by TCWC Perth. The JTWC then declared early the next day that the disturbance had dissipated as it crossed 90E and moved into RSMC La Réunion's area of responsibility. TCWC Perth continued to monitor the tropical low as it slowly developed further until early on September 20 when RSMC La Réunion 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. However, they released their final advisory later that day, as convection had dissipated in the northern quadrants of the system.Tropical Disturbance 03
Early on November 7, the JTWC issued a Tropical Cyclone Formation Alert on a system north of Diego Garcia. Later that day, RSMC La Réunion 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.Intense Tropical Cyclone Anja
RSMC La Réunion 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 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, while remaining well away from land. The system displayed annular characteristics and was very small; its diameter was and it displayed a pinhole eye. 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
On November 22, RSMC La Réunion commenced issuing advisories for Tropical Disturbance 05 about 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, 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 along coastal areas with some reaching. In the nearby Comoros Islands, waves were similarly high, with the highest reaching.
Intense Tropical Cyclone Cleo
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. 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 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
On December 12, a zone of disturbed weather formed in the Southern Indian Ocean near the border with the Australian region. 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.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. It then reversed its direction of motion and headed east-southeast while strengthening to a Severe Tropical Storm. 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.
On December 29, the remnants of David brought heavy rain to the islands of Mauritius and Réunion. Most of Mauritius recorded over of rain within a 24-hour span, with a maximum of 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.