2011 Atlantic hurricane season

Many storms, modest strength

Twenty tropical cyclones appear in the archive for 2011, and nineteen of them reached tropical storm force, the one exception being a short-lived depression east of the Cape Verde Islands in late August. That total tied 2011 with 1887, 1995, 2010 and 2012 for the fourth-highest number of named storms in the Atlantic record, well above the 1981 to 2010 average of about twelve. Hurricanes were far less plentiful: seven formed against an average of about six, and four of them reached major hurricane strength against an average of about three. The season's ACE of 126.3 sat above the range NOAA associates with an average season, but it was modest for a year with so many storms, because many of them were brief, weak or both.

Forecasters had expected a busy year. A La Niña that persisted from 2010, warmer than average sea surface temperatures in the tropical Atlantic and the ongoing warm phase of the Atlantic multidecadal oscillation all pointed to above-normal activity, and NOAA's May outlook called for 12 to 18 named storms. After a fast start to the season, NOAA raised that range to 14 to 19 in early August. Lower than average wind shear and warm waters duly supported frequent development, although many systems formed at higher latitudes or in marginal environments where they could not grow strong.

The site's counts come from IBTrACS, using US-agency one-minute winds during the tropical stage, and for 2011 they match the NHC best-track totals of 19 named storms, 7 hurricanes and 4 major hurricanes quoted in the season article. The count includes an unnamed tropical storm between Bermuda and Nova Scotia in early September, which the National Hurricane Center treated as a non-tropical low at the time and added to the record only in its post-season review.

How the season unfolded

The season got going late. Tropical Storm Arlene formed in the Bay of Campeche on 28 June, nearly a month after the official start, and after it dissipated over Mexico on 1 July the basin stayed quiet for about two weeks. The second half of July then produced three tropical storms in quick succession: Bret and Cindy, both born from the same stalled front off the United States East Coast and both carried away to the northeast, and Tropical Storm Don, which crossed the Gulf of Mexico toward Texas but fell apart so quickly that it reached Padre Island as only a depression.

August was the busiest month, with eight tropical cyclones and seven named storms, one short of the record for the month. Most of them were small or short-lived. Tropical Storm Emily struggled through strong shear across the northeastern Caribbean and degenerated near Hispaniola; Franklin and Gert were brief systems near Bermuda; and Tropical Storm Harvey came ashore in Belize and again in Mexico. The run of weak storms ended with Hurricane Irene, which became the season's first hurricane on 22 August over Puerto Rico. Tropical Storm Jose, sheared by Irene's outflow near Bermuda, and Hurricane Katia, which formed off Africa on 29 August, closed the month.

Early September was crowded. The unnamed tropical storm, Tropical Storm Lee in the northern Gulf of Mexico, Katia over the open Atlantic, and then Maria and Nate followed within days of one another, and on 8 September Nate, Katia and Maria were all active at once. Hurricane Maria stayed disorganized for much of its life, degenerating near the Leeward Islands before regenerating, reaching hurricane strength near Bermuda and landing in Newfoundland on 16 September. Hurricane Nate, which formed from a stalled frontal trough in the Bay of Campeche, drifted slowly, briefly became a hurricane on 8 September and made landfall near Tecolutla, Veracruz, as a weakened tropical storm.

The late season belonged to long-lived storms far from land. Hurricane Ophelia formed east of the Lesser Antilles on 20 September, weakened to a remnant low under shear and then regenerated into a much stronger storm. Hurricane Philippe, which formed south of the Cape Verde Islands on 24 September, spent about two weeks battling shear and dry air, including shear from Ophelia's outflow, before reaching hurricane strength in early October; its record of 384 hours is the longest of the season. October then added a single storm, Hurricane Rina in the western Caribbean, and November added Tropical Storm Sean, which began as a subtropical storm southwest of Bermuda and became extratropical on 11 November.

The strongest storms

Two storms shared the season's highest wind. Hurricane Katia, listed by the site as the season's strongest, crossed the Atlantic from near the Cape Verde Islands, became a hurricane on 1 September but was held back for several days by unfavorable conditions, and then intensified as it began to recurve, peaking at 120 kt as a Category 4 hurricane on 6 September with a central pressure of 942 hPa. It weakened almost immediately under shear and over cooler water and became extratropical south of Newfoundland on 10 September. Hurricane Ophelia matched that 120 kt peak on 2 October, and its pressure of 940 hPa was the lowest of the season, after a comeback from a remnant low only a week earlier.

Hurricane Irene peaked at 105 kt, Category 3, on 24 August, shortly before it crossed the southeastern Bahamas; its lowest pressure, 942 hPa, came two days later as its unusually large circulation filled a wide area without a particularly intense inner core. Hurricane Rina was the fourth major hurricane. It formed near Isla de Providencia on 23 October and deepened rapidly over warm Caribbean water, reaching 100 kt, Category 3, late on 25 October, but shear and drier air weakened it to a tropical storm before it reached the Yucatán Peninsula.

The remaining three hurricanes were all Category 1 at their peaks. Philippe reached 80 kt on 6 October after two separate spells at hurricane strength, Maria 70 kt near Bermuda on 16 September and Nate 65 kt in the Bay of Campeche on 8 September.

Hurricane Irene

Irene formed east of the Lesser Antilles on 21 August, passed over Saint Croix and Puerto Rico, and then ran parallel to the north coast of Hispaniola before crossing Crooked Island, Acklins and Long Island in the Bahamas as a Category 3 hurricane. It weakened gradually as it turned north, made landfall near Cape Lookout, North Carolina, at 1200 UTC on 27 August with winds of 75 kt, then came ashore again at Brigantine Island, New Jersey, on 28 August at 60 kt and passed over Brooklyn and Manhattan a few hours later at 55 kt. It became extratropical near the New Hampshire and Vermont border early on 29 August.

The storm's worst effects came from water rather than wind. Storm surge cut several breaches in Highway 12 on the North Carolina Outer Banks and flooded parts of southern Chesapeake Bay, a surge of 3 to 6 feet caused hundreds of millions of dollars in damage in New York City and on Long Island, and power failures reached up to 3 million residents. Rainfall of 4 to 7 inches produced catastrophic inland flooding in New Jersey, New York and New England; in southern Vermont nearly 2,400 roads, 300 bridges and 800 homes and businesses were damaged or destroyed in what the NHC expected to rank as the state's second-worst flood after November 1927, and three towns in the Catskills were left uninhabitable.

The NHC attributes 48 direct deaths to Irene: 40 in the United States, including Puerto Rico, 5 in the Dominican Republic and 3 in Haiti, with none reported in the Bahamas, where the hurricane was strongest. Its revised estimate of damage in the United States is $15.8 billion in 2011 dollars, combining doubled insured losses with National Flood Insurance Program flood claims. The World Meteorological Organization retired the name Irene in April 2012.

Other landfalls and impacts

Tropical Storm Lee formed in the Gulf of Mexico on 2 September, turned subtropical as its wind field spread out, and made landfall near Intracoastal City, Louisiana, on 4 September. Surge from Lake Pontchartrain flooded more than 150 homes in Jefferson and St. Tammany parishes, 10 to 15 inches of rain fell over parts of Louisiana and Mississippi, and a tornado spawned by Lee damaged about 400 homes in Cherokee County, Georgia. The remnants then fed some of the most severe flooding in the history of the Mid-Atlantic, along the Susquehanna River and its tributaries: about 100,000 people were evacuated in Pennsylvania and 20,000 were ordered out of Binghamton, New York. The NHC counts 3 direct deaths during Lee's (sub)tropical stage and at least 12 more, reported by the media, from flooding linked to its remnants. It cites an estimated $315 million in US insured losses and more than $1 billion in flood damage in media reports, while the season article puts Lee's total damage at about $2.8 billion in 2011 dollars.

Mexico took repeated blows from weaker storms. Tropical Storm Arlene came ashore near Cabo Rojo, Veracruz, on 30 June, and Mexico's National Meteorological Service reported 22 deaths, mostly in floods and mudslides, though how many were direct is unclear; the season article puts Arlene's damage at about $223 million in 2011 dollars. Tropical Storm Harvey caused five deaths in Mexico in August, three of them in a landslide in Oaxaca. Hurricane Nate caused four direct deaths when workers evacuating the Trinity II oil rig in the Bay of Campeche were forced to abandon their lifeboat, and one indirect death from lightning in Veracruz, where about 800 homes were damaged. Rina, by contrast, reached the coast near Paamul, Quintana Roo, as a 50 kt tropical storm and caused no significant damage or casualties.

Several storms that never made a destructive landfall still reached land in other ways. Tropical Storm Emily's rains caused landslides in Martinique, where one indirect death occurred, flooded roads in Puerto Rico and damaged about 300 homes in Haiti. Hurricane Maria's rains flooded homes in Puerto Rico. After becoming extratropical, Hurricane Katia brought gusts above 70 kt to Northern Ireland, northern England and Scotland on 12 September, cutting power to thousands of homes; media reports tied one direct and one indirect death in England to the storm, and the season article estimates about £100 million in damage in the United Kingdom. Hurricane Ophelia's remnants caused flooding in Newfoundland, where Maria had also landed weeks earlier.

Names and records

The 2011 list was the one used in 2005, with the names retired after that season replaced. As a result, Don, Katia, Rina and Sean were used for the first time in 2011. Irene became the only name retired from the 2011 list and was replaced by Irma.

The unnamed tropical storm of 1 to 2 September illustrates how the record can change after a season ends. Operationally, the NHC issued no advisories because its thunderstorms were intermittent and it seemed embedded in a front; only the post-season review, drawing on data that had not been available in real time, concluded that it briefly had enough tropical character to count as a tropical storm.