It is greatly intriguing that clear predictions about the power and progress of Hurricane Katrina were ignored by the authorities.
THE future will continue to wonder why, despite good forecasting of hurricane activity in the Atlantic in 2005 and adequate warnings about Hurricane Katrina as it gathered intensity in its path through the Gulf of Mexico, there was extreme slackness in the preparations of the vulnerable States of the United States along the eastern coast. Katrina was one of the most powerful and destructive storms on record for the Atlantic Basin.
Consider the unusually strong language of the alert issued by the New Orleans forecast office of the National Weather Service (NWS) on the morning of August 28, almost 18 hours before the onset of hurricane conditions. "The document is unparalleled to my knowledge in the boldness of its proclamations and absolute absence of ambiguity in its doomsday declaration. This statement is something worth keeping in the limelight when all the `there was no warning' nonsense inevitably erupts," said Anton Seimon of Columbia University in an e-mail message to his atmospheric scientist friends. The actual devastation seen was not far from the predictions in the alert.
An August update to the Atlantic Hurricane Season Outlook, issued on August 2 by the NWS's Climate Prediction Centre (CPC) under the National Oceanic and Atmospheric Administration (NOAA), called for a 95-100 per cent chance for an above-normal season. The Atlantic Hurricane Season officially runs from June 1 to November 30. An average hurricane season features 10 tropical storms (maximum sustained windspeed of 34-64 knots or 63-119 kilometres per hour), of which an average of six become hurricanes (maximum sustained windspeed of over 119 kmph) and two become major hurricanes (maximum sustained windspeed exceeding 176 kmph, categories 3-5 on the Saffir-Simpson Hurricane Scale).
The vast majority of tropical storms and hurricanes typically occur during August-October. However, this year, July was a record-breaking month for hurricane activity in the Atlantic. There were more named storms recorded in the month of July than ever in the hurricane record book history. There were five named tropical storms in July: Cindy (July 6) made landfall in Louisiana, Dennis (July 9) hit Cuba and landed in the Florida Panhandle, Emily (July 19) swept the Bahamas and into the North Atlantic Ocean and Gert (July 24) made landfall in Mexico's east coast.
In fact, during July, investigators from the National Aeronautics and Space Administration (NASA) and the NOAA flew sophisticated research aircraft within and above these storms to understand better the processes leading to the birth and intensification of hurricanes.
According to Jeffrey Halverson, senior weather meteorologist at NASA's Goddard Space Flight Centre (GSFC), Emily was the most powerful hurricane that NASA had ever flown over. Emily and Dennis were both strong hurricanes, meaning Category 3 or higher. "It is highly unusual for two strong hurricanes to develop in close succession as early as July in the Atlantic Hurricane Season," Halverson said.
What was the reason for this record-setting number of named storms, and that too before the peak of the season? According to satellite data of NASA and the NOAA, the winds and sea surface temperatures (SSTs) were perfect during the month of July to help these five tropical cyclones to form. Satellite data on several occasions in July showed rotating winds over the ocean's surface, precursors to cyclone development, and these gave rise to the five storms.
Hurricane development requires that the rising warm moist air remain stacked vertically to produce very deep cyclonic activity. Wind shear prevents this from happening and the air that needs to rise high in the atmosphere is blown in varying directions depending upon the height. During July, the amount of wind shear in the Atlantic was minimal.
Warmer than normal SSTs were also a key to causing the record number of storms. Tropical cyclones (over the Atlantic) require ocean surface temperatures in excess of 28oC to fuel evaporation and the rising air that helps create thunderstorms in a tropical cyclone. The SSTs in the tropical Atlantic and Gulf of Mexico were far greater than this threshold value beginning July and continued to rise to 30oC and more. "Hurricane wise we are in an incendiary situation," Bill Ptzert, oceanographer at NASA's Jet Propulsion Laboratory (JPL), had warned. "These toasty SSTs are high-octane fuel for September hurricanes," he had said. September is usually the busiest month for hurricanes.
"Much of the season's activity is still to come," Gerry Bell, the lead meteorologist on the NOAA's Atlantic Hurricane Seasonal Outlook, said. The updated outlook, based on data and events of July, predicted a seasonal total of 18 to 21 tropical storms, with nine to 11 becoming hurricanes (the climatological mean is six) and five to seven of them becoming major hurricanes (the mean is two or three). Close on the heels of Katrina, Hurricane Ophelia developed into a major one but weakened and, fortunately, avoided landfall. The outlook predicted the "total seasonal activity" to be 180-270 per cent of the median.
"Total seasonal activity" refers to the collective intensity and duration of Atlantic tropical storms and hurricanes occurring during a given season. The NOAA uses a measure for this called the Accumulated Cyclone Energy (ACE) index. ACE is a wind energy index, defined as the sum of the squares of the estimated six-hourly maximum sustained surface windspeed for all named systems (which are at least tropical storm strength). The categorisation of a hurricane season as `above-normal', `near-normal' and `below-normal' - in particular, the 180-270 per cent of the median value - is with reference to the ACE index together with the following three parameters: numbers of tropical storms, hurricanes and major hurricanes.
The expected ACE index for August-November, according to this early August outlook, is about 10-200 per cent of the median. The NOAA outlook said: "The predicted nearly 100 per cent chance of above-normal season is higher than the 70 per cent likelihood indicated in NOAA's pre-season outlook issued on May 16. The increased certainty reflects the fact [that] the atmospheric and oceanic conditions favouring hurricane formation that were predicted in May are now in place. These conditions, combined with high levels of activity already seen make an above-normal season nearly certain." The predicted high levels of activity during the remainder of the season are comparable to those seen from August to October during the very active 2003 and 2004 seasons, the outlook said.
Besides these operational forecasts of the NWS and the CPC, other studies in the research mode too had predicted an intensely active hurricane season. An "extended range" forecast of seasonal activity, monthly activity and U.S. landfall strike probability by the Department of Atmospheric Science, Colorado State University, also had similar predictions. The forecast used a statistical model (based on predictors derived from 55 years of global data).
In an August 5 update of its May forecast following the "increased favourability of several seasonal predictors over the past two months", the forecasters estimated that 2005 will have about 20 named storms, 10 hurricanes (average is 5.9), 95 named storm days (average is 49.1), 55 hurricane days (average is 24.5), six intense (category 3-4-5) hurricanes (average is 2.3) and 18 intense hurricane days (average is 5.0). "We expect [the] Atlantic basin tropical cyclone activity in 2005 to be about 235 per cent of the long-term average. The probability of U.S. major hurricane landfall is estimated to be well above the long-period average. This year is expected to continue the past-decade trend of above-average hurricane seasons," they wrote.
It has been opined variously that the unprecedented hurricane activity is related to human-induced climate changes. "There is no evidence that this is the case," say the Colorado researchers. "If global warming were the cause of the increase in U.S. hurricane activity, one would expect to see an increase in tropical cyclone activity in the other storm basins (West Pacific, East Pacific, Indian Ocean, etc.) as well. This has not occurred. When tropical cyclones worldwide are summed, there has actually been a slight decrease since 1995. In addition, it has been well-documented that the measured global warming during the 25-year period of 1970-1994 was accompanied by a downturn in [the] Atlantic basin hurricane activity over what was experienced during the 1930s through the 1960s," the estimate adds.
Historically, according to the NOAA, Atlantic hurricane activity has exhibited very strong multi-decadal variability, with alternating periods, lasting several decades, of generally above-normal or below-normal activity. These multi-decadal fluctuations in hurricane activity result entirely from differences in the number of hurricanes and major hurricanes forming from tropical storms. Hurricane seasons during 1950-2004 have averaged 13.6 tropical storms, 7.8 hurricanes, 3.8 major hurricanes and an average ACE index of 159 per cent of the median, according to the NOAA. The year 2005 will be the seventh hyperactive season in the past 11 years. In contrast, in the preceding 1970-94 period, hurricane seasons averaged nine tropical storms, five hurricanes and 1.5 major hurricanes.
But, more important, the NOAA outlook had this important warning: "Although the conditions that produce hurricane landfalls are well known, they are often related to the daily weather patterns rather than the seasonal climate patterns, and are very difficult to predict at these extended ranges. As a result, it is currently not possible to confidently predict the number or intensity of landfalling hurricanes at these extended ranges, or whether a given locality will be impacted by a hurricane this season. Nonetheless, given the forecast of above-normal activity for the remainder of the season, it is imperative that residents and governments in hurricane-vulnerable communities have a hurricane preparedness plan in place." This warning is particularly from the point of view of Katrina's development as it moved towards the coast and gathered intensity all too quickly and unexpectedly. It is thus greatly intriguing why such clear warnings seem to have gone unheeded.
On August 24, the first signatures of Katrina curling up into a major tropical storm were captured in the satellite images. Katrina had formed late on August 23 from a broad area of low pressure in the Central Bahamas and had just then become the 11th named storm of the 2005 Atlantic Hurricane Season. Moving northwestward, it had developed quickly into a tropical storm by 11 a.m. (local time) the next morning. With winds of 84 kmph, the storm had started acquiring the shape of a swirling hurricane and was expected to get stronger as it approached the south Florida coast, possibly becoming a Category 1 hurricane before arriving on shore.
It was expected then that, given its proximity to the Florida coast already, Katrina would not have enough time to develop into a major hurricane. Also, satellite images showed that the core of Katrina was devoid of deep convection. At that time there was more concern about Katrina's rains and consequent flooding as the storm was moving very slowly, at about 13 kmph, and was expected to slow down further as it moved over land. This meant that heavy rain would linger over a given area and precipitation in excess of 25 cm could be expected. By noon of August 25, Katrina had become a Category 1 hurricane with windspeeds of about 120 kmph.
Even though it was only a Category 1 hurricane as it passed over south Florida, it left behind much destruction in its wake, killing nine persons and causing extensive damage. But as it blew over the warm Gulf of Mexico, it began to gain strength very quickly and by August 26-27, it had become a Category 3 hurricane. Experts warned that by the time it reached land on August 29, it may become a full-blown Category 4 storm.
Early on August 27, the eye of the hurricane was located about 680 km southeast of the mouth of the Mississippi river and it was moving at a speed of about 11 kmph. But, suddenly overnight, within a span of nine hours, Katrina strengthened into a Category 5 hurricane with a sustained windspeed of about 260 kmph. The National Hurricane Centre (NHC) sent out a special advisory at 8 a.m. on August 27, after recording the sudden gain in the hurricane's strength from the warm waters of the Gulf. To date, only three Category 5 hurricanes have struck the U.S. coast since hurricane records began to be kept.
According to the NHC, a Category 5 hurricane causes storm surges of over six metres above normal and complete roof failure on many residential and industrial buildings. All shrubs, trees and signs will be blown down. Severe window and door damages will occur. Low-lying escape routes will be cut by rising water three to five hours before the arrival of the centre of the hurricane. Major damage to lower floors of all structures located less than five metres above sea level and within 500 m of the shoreline will occur and massive evacuation of residential areas on low ground within 8-15 km of the shoreline may be required.
This should have been seen as particularly relevant by the New Orleans administration as most of the city lies below the sea level and exists with the help of levees and pumps.
On August 28, Katrina turned slightly eastward before slamming into the shore. It thus redirected the storm's most potent winds and rain away from the vulnerable, low-lying areas of New Orleans. But this did not mean that New Orleans was spared of Katrina's fury; it was still battered by winds of over 230 kmph and six-metre-high storm surges. Katrina weakened slightly overnight to Category 4 and its eastward movement put the western eyewall - the weaker side of the strongest winds - over New Orleans. One can well imagine what the impact would have been had the hurricane hit New Orleans with full intensity.
The total damage has been placed at $125 billion and the death toll, as yet variously estimated, is expected to run into thousands. In a study of the deadliest and costliest hurricanes during the 20th century, NOAA scientists had said this: "One of the greatest concerns of the NWS hurricane preparedness officials is that the statistics will mislead people into thinking that no more large loss of life will occur in a hurricane because of our advanced technology... [We] have repeatedly emphasised the great danger of a catastrophic loss of life in a future hurricane if proper preparedness plans for vulnerable areas are not formulated, maintained and executed."
Prophetic words after what happened to New Orleans and its neighbourhood.