Meteorologist, Centro Nacional de Pronósticos, Instituto de Meteorología

Journal TEMAS No. 73: 39-43, January-March 2013

Cuba has a very long history of intense hurricanes that have caused great human and material losses. The hurricane of 1527, the first one remembered for its effects, caused great destruction in the town of Trinidad and sank part of Pánfilo de Narváez's fleet. In Havana, the so-called Storm of San Rafael, on October 24, 1692, is the first one in its recorded history. Various other hurricanes also hit the capital thereafter: one on October 15, 1768 knocked down seventy varas[1] of the thick wall that bordered the city; those of 1792 and 1810 caused serious damage, and the height of the waves during the latter even surpassed by eight varas the flagpoles of the waterfront fortresses.

Such events were followed by a high-intensity hurricane in 1844 and another in 1846, known as the San Francisco de Borjas Storm, the most intense that has ever affected Havana, with hurricane-force winds that were felt even in the vicinity of the current limits of the eastern provinces. This very strong system is one of the few cases of category 5 storms (winds exceeding 250 km/h) on the Saffir-Simpson scale that have battered the Cuban territory. As it made its way through the city, the barometers recorded a minimum atmospheric pressure of 916 hPa, the lowest ever in Cuba during this kind of meteorological phenomenon.

However, the greatest catastrophes in the history of the island were caused by hurricanes in the 20th century. The one of November 9, 1932 in Santa Cruz del Sur, Camagüey, category five, brought with it a storm surge almost seven meters high, caused the disappearance of the city and nearly all its inhabitants, and the death toll reached 3,033. Based on the intensity of its winds, Hurricane Flora (October 4 to 7, 1963) was not classified as a high-intensity event, but it produced heavy rains for 72 hours in the eastern region, home to Cuba’s highest mountains and largest rivers. The 1,800 mm of rainfall caused significant flooding which, regrettably, took the lives of 1,150 people. Other major hurricanes lashed against Havana and western Cuba in 1926 and 1944, and central Cuba’s northern coast in 1933; another one destroyed the city of Cienfuegos in 1935; and two big ones hit most of the western part of the Island in 1948 and the central provinces in 1952, respectively.

Since the late 1960s and until 1995, only Hurricane Kate, a low-intensity storm, is remembered. The rest of the Atlantic basin has saw a decline in cyclonic activity. However, this area has registered more high-intensity hurricanes since the mid-1990s than in any other known period. Is this fact related to climate change?

Variability in the North Atlantic

Research has shown that periods of strong and weak cyclonic activity have alternated in the North Atlantic basin for many years. Detected since the 19th century, they usually last from two to three decades, although this period may vary.

In Cuba, this variability has been observed in the number of tropical storms hitting the country every year, with totals ranging from zero to six (1909), and in the number of hurricanes, from zero to four (1886 and 1909). In addition to this interannual oscillation, there are active and inactive cycles, with alternating high and low frequencies. Among them, the 1920s and the period between 1973 and 1994 stand out as the two main periods of low activity. Despite the decrease observed in the latter period, there were disastrous tropical cyclones, such as Frederic (1979), Alberto (1982) and Kate (1985), due to the torrential downpours during the first two and the extensive area covered by the latter. Between 1909 and 1952 (forty-four years) twelve of the fourteen intense hurricanes that developed in the 20^th century hit the island, which bears a certain similarity to the outbreak that occurred between 1844 and 1888 (forty-five years), when eight of the eleven strongest hurricanes of the 19^th century affected the island.

We are now experiencing a new period of great cyclonic activity. Since 1995, nine hurricanes have hit Cuba, five of them of high intensity (categories 3, 4 or 5). It is interesting to note that these intense events took place between 2001 and 2012.

Therefore, these periods of low and high hurricane activity cannot be related to climate change. Studies by Dr. William M. Gray suggest that the cause lies in thermohaline circulation, i.e., that of warmer high salinity waters from the global ocean alternating from time to time in the North Atlantic. ⁽¹⁾ Wide fluctuations in the frequency and intensity of tropical storms complicate the detection of actual long-term trends, also hindered by significant limitations in the availability and quality of global historical data. Thus, at the global level, uncertainty persists as to whether past changes in cyclone activity have outstripped variability due to natural causes.

Nevertheless, the current period of high storm activity in the Atlantic has a distinctive feature: the number of high-intensity hurricanes and their rapid intensification. It is almost obvious that another factor is playing a role today: climate change and Atlantic hurricanes. Whether and to what extent the characteristics of tropical cyclones are changing has been the object of much research, sometimes with contradictory results.

The World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) established the joint Intergovernmental Panel on Climate Change (IPCC) in 1988, in particular to make a comprehensive, objective and transparent assessment of all the relevant scientific, technical and socio-economic information, in order to help understand the basis of the risks associated with human-induced climate change and its potential impacts and the options for adaptation and mitigation. Starting in 1990, the IPCC has produced several special reports, methodologies, technical papers and other documents which have since become official references for policymakers and scientists.

The latest estimates of the IPCC report (2007) point to a significant increase in extreme temperatures toward the end of the 21^st century, as well as to the likelihood that the frequency of heavy precipitation or the proportion of total rainfall derived from it will increase in the 21^st century over many areas, and that the average tropical cyclone maximum wind speed will increase, although this increase may not occur in all ocean basins and the global frequency of tropical cyclones will decrease or remain largely unchanged. ⁽²⁾

Other studies by James B. Elsner et al. ⁽³⁾ in the United States, using global satellite data, concluded that Atlantic hurricanes are getting stronger on average, with a thirty-year trend that has been related to an increase in ocean temperatures over the Atlantic Ocean. Over the rest of the tropics, however, possible trends in tropical storm intensity are less obvious, owing to the unreliability and incompleteness of the observations.

On the other hand, Thomas R. Knutson et al. ⁽⁴⁾ consider it premature to conclude that human activity is already producing a detectable modification in hurricane activity in the Atlantic, but they point out that anthropogenic warming will probably cause a global 2% to 11% increase in the average intensity of hurricanes by the end of the 21^st century, according to the projection of models for an IPCC A1B scenario. This would increase the percentage of destructive potential per hurricane, assuming there is no reduction in hurricane size.

They also state that some ocean basins are very likely to see a larger number of high-intensity hurricanes than the aforesaid mean value. This rise in intensity is stipulated in spite of the fact that there may be a decrease of, or little change in, the global number of tropical cyclones. Likewise, by the end of this century, global warming would result in substantially higher rainfall rates than those in the current climate, with a projection, according to the models, of 20% more rainfall averaged over a hundred kilometers from the hurricane core.

Early warning and protection of the population

Hurricanes will be more intense in the 21^st century; that is, the three most dangerous elements of these events will increase: winds, storm surges in coastal areas that are increasingly more populated and economically active, and rainfall. Consequently, risk and vulnerability will increase significantly.

In view of this scenario, it is imperative to adopt a strategy of adaptation to this type of weather event in order to reduce possible loss of life and material damage through the proper and effective implementation of preventive measures.

Hurricane prevention plans in Cuba

The surveillance and forecasting of the trajectory and future intensity of a tropical storm is a hard and complex operational task that involves a great deal of responsibility, since decisions have to be made in a relatively short time, sometimes with insufficient data, which have a direct impact on the population and the economy. It is also a team effort, in which every step counts. Different tasks precede the preparation of a forecast and the issuance of a warning, namely: gathering data from weather stations and observation systems, including satellites and radars; working with national and international communications systems, which transfer the flow of information to and from the National Center for Weather Forecasts of the Institute of Meteorology (CNPIM); data processing on workstations and computers; use of forecast models, both national and foreign; analysis of the available information, first to make a diagnosis and then to forecast the hurrican’s path and intensity. In addition to the statistical guidance models, the most important factor comes into play here: the human being, the meteorologists with their knowledge and experience, often bound to be more efficient than the best numerical models.

Then comes an impact analysis and forecast of the dangers that the event may represent to certain areas, followed by the drafting of the Tropical Storm Warning and the coordination of efforts between the CNPIM management, the government and the National Civil Defense Command Post (EMN-DC). The latter advises the National Defense Council to declare the stages and take the measures that it deems necessary. Finally, the meteorologists communicate the warning to the population and keep it updated on the event through the national television and radio networks.

Likewise, the CD specialists give people their own instructions in this respect.

The interaction between forecasters and the national CD system is highly valuable because the indications and actions of this body are able, on behalf of the State, to reduce loss of life and material damage. The CNPIM provides the scientific basis for the implementation of protective measures throughout the country; however, the Cuban system has a much broader scope since, by law, the top responsibility for the fulfillment of the measures suggested by the DC lies with the principals of every school and the directors or managers of every workplace. The same goes for every level of government. Therefore, it is safe to say that the system engages all citizens.

A significant factor is the education of the population and its high level of schooling. Our primary, secondary and university education system includes the teaching of civil defense topics and the fundamentals of meteorology. Our schools also organize vocational study circles and municipal, provincial and national competitions that encourage learning about these subjects. Meteorologists take an active part in our education and awareness programs giving lectures in workplaces and schools or in radio and television programs—such as Universidad para Todos [University for All] in our learning channels—devoted to training courses on hurricanes, meteorology and climatology, and climate change.

Hazard and vulnerability studies, carried out throughout the country, allow decision-makers to learn which areas are most likely to be affected and how it could happen. The emphasis is on prevention. The response to the event is similar to that during preparedness, when there is no threat yet, and this helps us to do everything better.

An important element is the information provided to the public, who must receive data on the hurricane and instructions that everybody can understand, simple and without technicalities. The fact that the message is communicated through multiple radio and television news broadcasts by well-known forecast specialists who use satellite and radar images and simple graphics showing the cone of probability of the hurricane's future pathway, makes it all the more reliable.

The Cuban Center for Weather Forecasts issues warnings on tropical cyclones of any classification and category forming in the Atlantic Ocean, the Caribbean Sea and the Gulf of Mexico. This information is broadcasted more frequently as the event approaches the country. When it is located east of the 55°W meridian or north of the 30°N parallel, there will be forecasts every single day at 6:00 p.m.; if a storm system develops within the aforesaid coordinates or crosses them, we issue warnings every twelve hours (at 6: 00 p.m. and 6:00 a.m.), and every six hours (at 6:00 p.m., 12:00 noon, 6:00 a.m. and 12:00 midnight) if the storm poses a danger to Cuba in the next seventy-two hours. When it is very close or already impacting the national territory, we may go on air with the warnings every three hours to give updates on the event’s location and wind intensity.

Furthermore, whenever there are indications of a potential danger in the shorter or longer term, that is, in three to five days, the CNPIM issues Early Warning notices, which is very useful to notify the authorities and decision-makers of the situation with plenty of time in advance. Giving information devoid of sensationalism helps arouse people’s response to the possible danger and stresses the need to be on the alert, but without sowing any panic at all. In periods of less than seventy-two hours, the advisories become part of the tropical storm warnings.

If an imminent threat of a tropical storm or any other major weather event exists, national television and radio crews go to the CNPIM headquarters and continuously broadcast from there the warnings and latest updates on the situation for as long as any part of the country is in danger. This is how we provide the population with official, unique and reliable information to which they always pay a great deal of attention.

Even if the press cannot match the immediacy of live TV coverage to issue these warnings, its supplementary reports in printed articles are very useful for people to receive further details about both the general meteorological situation and the threat of the tropical cyclone in particular.  Moreover, all media outlets promote the efforts deployed to protect the population and the economy through the guidelines issued by the EMN-DC and the Provincial Defense Councils.  The design of these guidelines takes into account that the evacuation of people must be completed before the onset of heavy rains likely to close off roads and before the tropical storm-force winds become hurricane-force winds. The EMN-DC also considers the particular features of the tropical cyclone (whether it is a tropical depression, a tropical storm or a hurricane): the intensity of the maximum winds and areas of intense rainfall that it brings, the situation of coastal areas in danger of floods or storm surges, the specific characteristics of the region at risk (coast, plain, mountains, rivers, etc.), and the state of the reservoirs and the water table.

It is worth mentioning that Cuba promotes a culture of prevention intended to reduce vulnerability and suffer less damage. In this regard, as mentioned above, education and preparedness play an essential role. Directive No. 1 of the Vice President of the National Defense Council, issued in 2006 and updated in 2010, is a fundamental instrument for these purposes.

Thanks to the comprehensive nature of the protection system that it has in place, Cuba boasts the lowest number of deaths caused by tropical cyclones in the entire area of the Atlantic, the Caribbean and the Gulf of Mexico, and it is even ahead of some highly developed nations in this indicator. In the eighteen years of the current period of great cyclonic activity, twenty cyclones of tropical storm or hurricane intensity have hit the island, for an average of 1.11 per year, as compared to one every two years in the past. Eight of those twenty events were of great intensity, for a record annual frequency of 0.444—the previous frequency was one every twelve years, for an annual frequency of 0.083. However, only fifty-two people lost their lives (82.7% of them as a result of high-intensity hurricanes). Twelve of those cyclones, including seven very powerful ones, claimed no lives at all.

Obviously, the Cuban experience in risk reduction in the face of these meteorological events can be described as very successful.

NOTES

1. See William M. Gray, Forecast of Global Circulation Characteristics in the next 25-30 Years, 21st NOAA Climate Workshop, Huntsville, AL, 1996.

2. Managing the risks of extreme events and disasters to advance climate change adaptation, Special Report of the Intergovernmental Panel on Climate Change (IPCC), 2012.

3. James B. Elsner et al., The Increasing Intensity of the Strongest Tropical Hurricanes, Nature, v. 455, n. 4, London, September 2008.

4. Thomas R. Knutson et al., Dynamical Downscaling Projections of Late Twenty-First-Century Atlantic Hurricane Activity: CMIP3 and CMIP5 Model-Based Scenarios, NOAA/Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, March 8, 2013.

Traduccion: Jesus Bran