During 2011, tropical cyclones formed within seven different tropical cyclone basins, located within various parts of the Atlantic, Pacific and Indian Oceans. The strongest tropical cyclone of the year was Typhoon Songda, with a minimum central pressure of 920 hPa (mbar). The costliest tropical cyclone of the year was Hurricane Irene, which caused $14.2 billion worth of damage. The deadliest tropical cyclone of the year was Severe Tropical Storm Washi, which killed 2,546 people. During the year, a total of 130 tropical cyclones had formed this year to date. 75 tropical cyclones had been named by either a Regional Specialized Meteorological Center (RSMC) or a Tropical Cyclone Warning Center (TCWC). Thirty-nine of these named systems eventually intensified into hurricane-equivalent tropical cyclones.
The most active basin in the year was the Western Pacific, which documented 21 named storms. North Atlantic basin documented 19 named storms, continuing the consecutive third-most active season trends from the previous year, due to the 2010–12 La Niña event. Conversely, the Eastern Pacific basin featured slightly more activity than the previous season, with 11 named storms. The least active basin in the year was the North Indian Ocean basin which documented only 2 named storms, the lowest since the 1993 season. Activity across the Southern Hemisphere were almost evenly spread, with the South-West Indian Ocean basin recording 10 tropical cyclones, the Australian region recording 17 tropical cyclones, and the South Pacific basin also recording 10 tropical cyclones, respectively. Twenty-one Category 3 tropical cyclones formed in the year, including three Category 5 tropical cyclones. The accumulated cyclone energy (ACE) index for the 2011 (seven basins combined), as calculated by Colorado State University was 573.8 units.
Tropical cyclones are primarily monitored by a group of ten warning centers, which have been designated as a Regional Specialized Meteorological Centre (RSMC) or a Tropical Cyclone Warning Center (TCWC) by the World Meteorological Organization. These are the United States National Hurricane Center (NHC) and Central Pacific Hurricane Center, the Japan Meteorological Agency (JMA), the Indian Meteorological Department (IMD), Météo-France (MFR), Indonesia's Badan Meteorologi, Klimatologi, dan Geofisika, the Australian Bureau of Meteorology (BOM), Papua New Guinea's National Weather Service, the Fiji Meteorological Service (FMS) as well as New Zealand's MetService. Other notable warning centers include the Philippine Atmospheric, Geophysical, and Astronomical Services Administration (PAGASA), the United States Joint Typhoon Warning Center (JTWC), and the Brazilian Navy Hydrographic Center(BNHC).
Global atmospheric and hydrological conditions
The strong La Niña from the previous year continued into 2011, whereby it peaked in January. Afterwards, it began weakening considerably, to the point where in May it was determined that a transition to neutral conditions took place. By the end of Summer, this neutral state continued to persist, although there were still remnants of the La Niña evident. Due to continued cooling of the Pacific, it was determined that the La Niña redeveloped, albeit in a weak state, which would then continue into the next year.
Summary
Systems January
During January 2011, a total of 12 tropical cyclones, all of them, formed within the southern hemisphere. No tropical cyclone was observed in the northern hemisphere. Of the systems, 7 further intensified to become named. Out of the systems, Wilma was the most intense tropical cyclone, with a minimum barometric pressure of 935 mbar/hPa. + Tropical cyclones formed in January 2011 Storm name Dates active Max windkm/h (mph) Pressure(hPa) Areas affected Damage(USD) Deaths Refs03 January 2–3 55 (35) 996Madagascar NoneNoneVania January 5–15 100 (65)973Vanuatu, Fiji, New Caledonia, New Zealand unknown unknown 04F January 5–7 185 (115)1002New Caledonia $25 million3 direct, 1 indirectVince January 10—15 75 (45) 986 None None None Zelia January 12—17 185 (115)943New Caledonia, Norfolk Island, New Zealand None NoneWilma January 19–29185 (115) 935Samoan Islands, Tonga, New Zealand$22 million307F January 20–2265 (40)996New Caledonia None NoneAnthony January 22–31 95 (60) 989Queensland MinorNoneBianca January 23–30175 (110) 949 Northern Territory, Western Australia Unknown2Yasi January 26–February 3 205 (125) 929Tuvalu, Fiji, Solomon Islands, Vanuatu, Papua New Guinea, Australia$3.6 billion104 January 30–31 45 (30) 998Réunion NoneNone13U January 31Not SpecifiedNot SpecifiedNoneNoneNone
February
10 systems formed and 5 named storms during February. + Tropical cyclones formed in February 2011 Storm name Dates active Max windkm/h (mph) Pressure(hPa) Areas affected Damage(USD) Deaths RefsBOB 01 February 2–345 (30) 1002Sri Lanka297 million18Zaka February 5–7 95 (60) 985NoneNoneNone15U February 8–13 55 (35)996NoneNoneNoneBingiza February 9–17155 (100) 957Comoros, MadagascarUnknown34AtuFebruary 13–24 165 (105)940Vanuatu UnknownNoneDianne February 14–22140 (85) 960Western Australia Minimal None Carlos February 14–27120 (75) 969Northern Territory, Western Australia $12.3 million None06 February 15–1845 (30)1000None NoneNone18U February 23–28 55 (35) 992 NoneNone None19U February 26–March 1Not Specified1000Northern TerritoryNoneNone
March
March was a relatively inactive month in which 11 systems formed, and only 3 received names. + Tropical cyclones formed in March 2011 Storm name Dates active Max windkm/h (mph) Pressure(hPa) Areas affected Damage(USD) Deaths Refs20U March 5Not SpecifiedNot SpecifiedNoneNoneNone21U March 7–8 45 (30) 1004NoneNoneNone12F March 7–9 45 (30) 1002VanuatuNoneNone22U March 10–15 Not SpecifiedNot SpecifiedNoneNoneNoneCheronoMarch 10–2375 (45)993Rodrigues Island None NoneArani March 14–1685 (50) 989Brazil None NoneBune March 22 – 29130 (80) 967Fiji NoneNone25U March 26–April 655 (35)994NoneNoneNone08 March 29–31 45 (30)1004NoneNoneNone26U March 30–April 1Not Specified 1006NoneNoneNone27U March 30–April 1Not Specified1006NoneNoneNone
April
+ Tropical cyclones formed in April 2011 Storm name Dates active Max windkm/h (mph) Pressure(hPa) Areas affected Damage(USD) Deaths Refs01W April 1–455 (35)1004NoneNoneNone02W (Amang) April 3–655 (35)1000Mariana IslandsNoneNone14F April 10–11 Not Specified1005Vanuatu NoneNone09 April 11–1695 (60) 985NoneNoneNone28U April 14–15 Not SpecifiedNot SpecifiedNoneNoneNoneErrol April 14–20100 (65)986Indonesia, Western Australia, Northern TerritoryNoneNone15F April 15–17 55 (35) 999NoneNoneNone16F April 28–30Not Specified1002NoneNoneNone
May
May was a mostly inactive month in which only 4 tropical cyclones formed, in which 2 received names. + Tropical cyclones formed in May 2011 Storm name Dates active Max windkm/h (mph) Pressure(hPa) Areas affected Damage(USD) Deaths RefsAere (Bebeng) May 5–1275 (45)992Philippines, Japan$34.4 million4817F May 10–11 55 (35)1000NoneNoneNoneSongda (Chedeng) May 19–29 195 (120)920Micronesia, Philippines, Japan $287 million17TD May 31–June 1 Not specified1004NoneNoneNone
June
+ Tropical cyclones formed in June 2011 Storm name Dates active Max windkm/h (mph) Pressure(hPa) Areas affected Damage(USD) Deaths RefsAdrian June 7–12220 (140) 944Southwestern Mexico NoneNoneSarika (Dodong) June 8–1175 (45) 996Philippines, China$248 million28ARB 01 June 11–1245 (30) 996India NoneNoneTD June 14–15Not specified 1004China NoneNoneHaima (Egay) June 16–2575 (45)985Philippines, China, Vietnam, Laos, Thailand $167 million18BOB 02 June 16–2365 (40)978IndiaNone 6Beatriz June 19–22 150 (90) 977Southwestern and Western MexicoNone4Meari (Falcon) June 20–27110 (70)970Philippines, China, Japan, Korea$1.24 million11ArleneJune 28–July 1100 (65) 993Central America, Mexico, Texas, Florida$223.4 million22
July
+ Tropical cyclones formed in July 2011 Storm name Dates active Max windkm/h (mph) Pressure(hPa) Areas affected Damage(USD) Deaths RefsCalvin July 7–10130 (80)984NoneNoneNoneGoring July 8–1045 (30)1000Taiwan, China NoneNoneMa-on (Ineng) July 11–24175 (110)935Northern Mariana Islands, Japan $50 million5Tokage (Hanna) July 13–1565 (40)1000NoneNoneNoneTD July 16–17Not specified1000China NoneNoneBret July 17–22110 (70) 995Bahamas, Bermuda, East Coast of the United States NoneNoneDora July 18–24 250 (155) 929Southwestern Mexico, Western Mexico, Baja California Peninsula, Southwestern United States MinimalNoneCindy July 20–22110 (70) 994Bermuda NoneNoneLAND 01 July 22–23 35 (25)990India None NoneNock-ten (Juaning) July 24–3195 (60) 985Philippines, China, Vietnam, Laos, Thailand $126 million128Muifa (Kabayan) July 25–August 9175 (110)930Micronesia, Caroline Islands, Philippines, Japan, China, Korea, Russia $480 million22Don July 27–3085 (50) 997Cuba, Yucatán Peninsula, Northeastern Mexico, Texas NoneNoneLando July 31–August 2Not specified1002PhilippinesNoneNoneEugene July 31–August 6220 (140)942NoneNoneNone
August
August was the most active month of 2011, with 18 systems forming in the month. + Tropical cyclones formed in August 2011 Storm name Dates active Max windkm/h (mph) Pressure(hPa) Areas affected Damage(USD) Deaths RefsEmily August 2–7 85 (50) 1003Antilles, Florida, Bahamas $5 million5Merbok August 2–995 (60)980None NoneNoneTD August 2–4 55 (35)1008Japan NoneNone13W August 8–14 55 (35) 1004NoneNoneNoneTD August 8–1055 (35)1008 NoneNoneNoneFranklin August 12–13 75 (45)1004Bermuda NoneNoneGert August 13–16100 (65)1000Bermuda NoneNoneFernanda August 15–19110 (70)992NoneNoneNoneGreg August 16–21 140 (85)979NoneNoneNoneHarvey August 19–22 100 (65) 994Lesser Antilles, Hispaniola, Central America, Mexico Minimal5TD August 20–25 55 (35)1004 NoneNoneNoneIrene August 21–28 195 (120)942Lesser Antilles, Greater Antilles, Turks and Caicos, Bahamas, East Coast of the United States, Vermont, Atlantic Canada $14.2 billion58Nanmadol (Mina)August 21–31185 (115) 925Philippines, Taiwan, China$1.49 billion38Talas August 23–September 595 (60) 970Japan$600 million 82Ten August 25–2655 (35)1006NoneNoneNoneJose August 26–2975 (45)1006BermudaNoneNoneKatia August 29–September 10 220 (140)942Lesser Antilles, East Coast of the United States, Canada, United Kingdom $157 million4Eight-E August 31–September 155 (35)1002Southwestern Mexico, Western MexicoNoneNone
September
September was a below-average month, with only 16 tropical cyclones forming in that month. + Tropical cyclones formed in September 2011 Storm name Dates active Max windkm/h (mph) Pressure(hPa) Areas affected Damage(USD) Deaths RefsUnnamed September 1–375 (45)1002NoneNoneNoneLee September 2–595 (60)986Gulf Coast of the United States, Eastern United States$2.8 billion18Noru September 2–6 75 (45)990 NoneNoneNoneKulap (Nonoy)September 6–1165 (40)1000Japan, Korea NoneNoneMaria September 6–16130 (80)983Lesser Antilles, Bermuda, Newfoundland, Europe$1.3 millionNoneNate September 7–11120 (75)994MexicoMinimal5Roke (Onyok) September 8–22155 (100)940 Japan, Russia, Alaska$1.2 billion 13TD September 13–15 Not specified1002TaiwanNone NoneSonca September 14–20130 (80)970 NoneNoneNoneOphelia September 20–October 3220 (140)940Leeward Islands, Bermuda, Newfoundland MinimalNoneHilary September 21–30230 (145)942Southwestern MexicoMinimalNoneBOB 03September 22–2345 (30)995IndiaUnknown42Nesat (Pedring) September 23–30 150 (90) 950 Philippines, China, Vietnam $2.12 billion 98Haitang September 24–27 65 (40) 996 China, Vietnam, Laos $20 million 25Philippe September 24–October 8 150 (90)976 Cape Verde None None Nalgae (Quiel) September 26–October 5 175 (110) 935 Philippines, China, Vietnam $250 million 18
October