Atlantic Hurricane Activity Research Articles

Influence of sequential hurricanes on nekton communities in a Southeast Florida estuary: Short-term effects in the context of historical variations in freshwater inflow

We examined nekton community-level responses to Hurricanes Frances and Jeanne, which made landfall 20 d apart in the St. Lucie estuary in southeastern Florida in 2004. The passage of these storms contributed to large freshwater discharges that exceeded 150 m3 s−1, as well as estuary-wide reductions in salinity and near-hypoxic conditions in the North Fork of the estuary that persisted for several months. Although such environmental variations are not uncommon, seasonal patterns of community structure were disturbed throughout much of the estuary, likely in response to uncharacteristically-rapid reductions in salinity. Immediately following the hurricanes, abundances of several freshwater and oligohaline taxa (i.e., blue crabCallinectes sapidus, shadDorosoma spp., and ladyfishElops saurus) increased markedly in the inner estuary, while abundances of several other fishes (i.e., striped mulletMugil cephalus, white mulletM. curema, lookdownSelene vomer, pigfishOrthopristis chrysoptera, and pinfishLagodon rhomboides) declined. Nekton communities recovered quickly, and by spring, community structure throughout much of the estuary was indistinguishable from pre-hurricane conditions. Although nekton communities were resilient to hurricane-related disturbances, projected increases in Atlantic hurricane activity and associated freshwater discharges over the coming decades may test the resilience of estuarine communities in Florida.

Impact of Atlantic multidecadal oscillations on India/Sahel rainfall and Atlantic hurricanes

Prominent multidecadal fluctuations of India summer rainfall, Sahel summer rainfall, and Atlantic Hurricane activity have been observed during the 20th century. Understanding their mechanism(s) will have enormous social and economic implications. We first use statistical analyses to show that these climate phenomena are coherently linked. Next, we use the GFDL CM2.1 climate model to show that the multidecadal variability in the Atlantic ocean can cause the observed multidecadal variations of India summer rainfall, Sahel summer rainfall and Atlantic Hurricane activity (as inferred from vertical wind shear changes). These results suggest that to interpret recent climate change we cannot ignore the important role of Atlantic multidecadal variability.

Influences of the Atlantic Warm Pool on Western Hemisphere Summer Rainfall and Atlantic Hurricanes

Abstract The Atlantic warm pool (AWP) of water warmer than 28.5°C comprises the Gulf of Mexico, the Caribbean Sea, and the western tropical North Atlantic (TNA). The AWP reaches its maximum size around September, with large AWPs being almost 3 times larger than small ones. Although ENSO teleconnections are influential on the AWP, about two-thirds of the large and small AWP variability appears unrelated to ENSO. The AWP is usually geographically different from the TNA; however, the AWP size is correlated with the TNA SST anomalies. During August to October, large AWPs and warm TNA are associated with increased rainfall over the Caribbean, Mexico, the eastern subtropical Atlantic, and the southeast Pacific, and decreased rainfall in the northwest United States, Great Plains, and eastern South America. In particular, rainfall in the Caribbean, Central America, and eastern South America from August to October is mainly related to the size of the AWP. Large (small) AWPs and warm (cold) TNA correspond to a weakening (strengthening) of the northward surface winds from the AWP to the Great Plains that disfavors (favors) moisture transport for rainfall over the Great Plains. On the other hand, large (small) AWPs and warm (cold) TNA strengthen (weaken) the summer regional Atlantic Hadley circulation that emanates from the warm pool region into the southeast Pacific, changing the subsidence over the southeast Pacific and thus the stratus cloud and drizzle there. The large AWP, associated with a decrease in sea level pressure and an increase in atmospheric convection and cloudiness, corresponds to a weak tropospheric vertical wind shear and a deep warm upper ocean, and thus increases Atlantic hurricane activity.

Atlantic hurricane trends linked to climate change

Increases in key measures of Atlantic hurricane activity over recent decades are believed to reflect, in large part, contemporaneous increases in tropical Atlantic warmth [e.g., Emanuel, 2005]. Some recent studies [e.g., Goldenberg et al., 2001] have attributed these increases to a natural climate cycle termed the Atlantic Multidecadal Oscillation (AMO), while other studies suggest that climate change may instead be playing the dominant role [Emanuel, 2005; Webster et al., 2005].Using a formal statistical analysis to separate the estimated influences of anthropogenic climate change from possible natural cyclical influences, this article presents results indicating that anthropogenic factors are likely responsible for long‐term trends in tropical Atlantic warmth and tropical cyclone activity. In addition, this analysis indicates that late twentieth century tropospheric aerosol cooling has offset a substantial fraction of anthropogenic warming in the region and has thus likely suppressed even greater potential increases in tropical cyclone activity.

The 2005 hurricane season: An echo of the past or a harbinger of the future?

Recent Atlantic hurricane activity raises several questions. For example, why was the 2005 season so early and active and are there similarities with the past? We show that parallels exist between 2005 and previously active years. Tropical Atlantic sea surface temperature (SST) anomalies beginning in winter aided the formation of early storms. On longer timescales SST, sea level pressure and zonal winds exhibit multidecadal variability; weaker easterlies during the positive phase of the Atlantic Multidecadal Oscillation (AMO) result (via ocean‐atmosphere interactions) in warmer water and increased hurricane activity. However, individual active years appear independent of the AMO phase.

Leading Tropical Modes Associated with Interannual and Multidecadal Fluctuations in North Atlantic Hurricane Activity

Abstract Interannual and multidecadal extremes in Atlantic hurricane activity are shown to result from a coherent and interrelated set of atmospheric and oceanic conditions associated with three leading modes of climate variability in the Tropics. All three modes are related to fluctuations in tropical convection, with two representing the leading multidecadal modes of convective rainfall variability, and one representing the leading interannual mode (ENSO). The tropical multidecadal modes are shown to link known fluctuations in Atlantic hurricane activity, West African monsoon rainfall, and Atlantic sea surface temperatures, to the Tropics-wide climate variability. These modes also capture an east–west seesaw in anomalous convection between the West African monsoon region and the Amazon basin, which helps to account for the interhemispheric symmetry of the 200-hPa streamfunction anomalies across the Atlantic Ocean and Africa, the 200-hPa divergent wind anomalies, and both the structure and spatial scale of the low-level tropical wind anomalies, associated with multidecadal extremes in Atlantic hurricane activity. While there are many similarities between the 1950–69 and 1995–2004 periods of above-normal Atlantic hurricane activity, important differences in the tropical climate are also identified, which indicates that the above-normal activity since 1995 does not reflect an exact return to conditions seen during the 1950s–60s. In particular, the period 1950–69 shows a strong link to the leading tropical multidecadal mode (TMM), whereas the 1995–2002 period is associated with a sharp increase in amplitude of the second leading tropical multidecadal mode (TMM2). These differences include a very strong West African monsoon circulation and near-average sea surface temperatures across the central tropical Atlantic during 1950–69, compared with a modestly enhanced West African monsoon and exceptionally warm Atlantic sea surface temperatures during 1995–2004. It is shown that the ENSO teleconnections and impacts on Atlantic hurricane activity can be substantially masked or accentuated by the leading multidecadal modes. This leads to the important result that these modes provide a substantially more complete view of the climate control over Atlantic hurricane activity during individual seasons than is afforded by ENSO alone. This result applies to understanding differences in the “apparent” ENSO teleconnections not only between the above- and below-normal hurricane decades, but also between the two sets of above-normal hurricane decades.

Anthropogenic and climatic influences on the eutrophication of large estuarine ecosystems

We examined the effects of anthropogenic and climatic perturbations on nutrient—phytoplankton interactions and eutrophication in the waters of the largest estuarine systems in the U.S.A., the Chesapeake Bay (CB), Maryland/ Virginia, and the Neuse River Estuary/Pamlico Sound (NRE/PS) system, North Carolina. Both systems have experienced large post‐World War II increases in nitrogen (N) and phosphorus (P) loading, and nutrient reductions have been initiated to alleviate symptoms of eutrophication. However, ecosystem‐level effects of these nutrient reductions are strongly affected by hydrologic variability, including severe droughts and a recent increase in Atlantic hurricane activity. Phytoplankton community responses to these hydrologic perturbations, including storm surges and floods, were examined and when possible, compared for these systems. In both systems, the resulting variability in water residence time strongly influenced seasonal and longer‐term patterns of phytoplankton biomass and community composition. Fast‐growing diatoms were favored during years of high discharge and short residence time in CB, whereas this effect was not observed during high discharge conditions in the longer residence time NRE/ PS. In the NRE/PS, all phytoplankton groups except summer cyanobacterial populations showed decreased abundance during elevated flow years when compared to low flow years. Although hurricanes affected the CB less frequently than the NRE/PS, they nonetheless influenced floral composition in both systems. Seasonally, hydrologic perturbations, including droughts, floods, and storm‐related deep mixing events, overwhelmed nutrient controls on floral composition. This underscores the difficulty in predicting seasonal and longer‐term phytoplankton production and compositional responses to nutrient input reductions aimed at controlling eutrophication of large estuarine ecosystems.

A Consolidated CLIPER Model for Improved August–September ENSO Prediction Skill

Abstract A prime challenge for ENSO seasonal forecast models is to predict boreal summer ENSO conditions at lead. August–September ENSO has a strong influence on Atlantic hurricane activity, Northwest Pacific typhoon activity, and tropical precipitation. However, summer ENSO skill is low due to the spring predictability barrier between March and May. A “consolidated” ENSO–climatology and persistence (CLIPER) seasonal prediction model is presented to address this issue with promising initial results. Consolidated CLIPER comprises the ensemble of 18 model variants of the statistical ENSO–CLIPER prediction model. Assessing August–September ENSO skill using deterministic and probabilistic skill measures applied to cross-validated hindcasts from 1952 to 2002, and using deterministic skill measures applied to replicated real-time forecasts from 1900 to 1950, shows that the consolidated CLIPER model consistently outperforms the standard CLIPER model at leads from 2 to 6 months for all the main ENSO indices (3, 3.4, and 4). The consolidated CLIPER August–September 1952–2002 hindcast skill is also positive to 97.5% confidence at leads out to 4 months (early April) for all ENSO indices. Optimization of the consolidated CLIPER model may lead to further skill improvements.

Hypersaline cyanobacterial mats as indicators of elevated tropical hurricane activity and associated climate change.

The Atlantic hurricanes of 1999 caused widespread environmental damage throughout the Caribbean and US mid-Atlantic coastal regions. However, these storms also proved beneficial to certain microbial habitats; specifically, cyanobacteria-dominated mats. Modern mats represent the oldest known biological communities on earth, stromatolites. Contemporary mats are dominant biological communities in the hypersaline Bahamian lakes along the Atlantic hurricane track. We examined the impacts of varying levels of hypersalinity on 2 processes controlling mat growth, photosynthesis and nitrogen fixation, in Salt Pond, San Salvador Island, Bahamas. Hypersalinity (> 5 times seawater salinity) proved highly inhibitory to these processes. Freshwater input from Hurricane Floyd and other large storms alleviated this salt-inhibition. A predicted 10 to 40 year increase in Atlantic hurricane activity accompanied by more frequent "freshening" events will enhance mat productivity, CO2 sequestration and nutrient cycling. Cyanobacterial mats are sensitive short- and long-term indicators of climatic and ecological changes impacting these and other waterstressed environments.

El Niño suppressing storms

A strengthening El Niño has suppressed overall tropical storm activity during the 2002 Atlantic hurricane season, the National Oceanic and Atmospheric Administration announced on 25 November. The hurricane season, which ended on 30 November, produced only four hurricanes, half the number during a typical year since 1995. Eight storm systems—twice the average amount—affected the U.S., however.NOAA hurricane forecasters at the agency's Climate Prediction Center, Hurricane Research Division, and National Hurricane Center had predicted normal to below‐normal overall storm activity, due to the strengthening El Niño, according to the agency. Climate Prediction Center director Jim Laver said that gaining a better understanding of the atmospheric conditions controlling seasonal hurricane activity is at the core of the agency's extended‐range hurricane outlooks. Laver said that while 2002 was the agency's fifth straight year of issuing accurate outlooks for overall hurricane season activity, “future success depends on more research into how global and regional climate patterns affect Atlantic hurricane activity.”

Testing for Trend in North Atlantic Hurricane Activity, 1900–98

Abstract The detection of a trend in hurricane activity in the North Atlantic basin has been restricted by the incompleteness of the record prior to 1946. In an earlier paper, the complete record of U.S. landfalling hurricanes was used to extend the period of analysis back to 1930. In this paper, a further extension is made back to 1900. In doing so, the assumption in the earlier paper of an exponential linear trend is relaxed and the trend is estimated nonparametrically. The results show no significant trend in basinwide hurricane activity over the period 1900–98.

A space–time model for seasonal hurricane prediction

AbstractA space–time count process model is explained and applied to annual North Atlantic hurricane activity. The model uses the best‐track data set of historical hurricane positions and intensities, together with climate variables, to determine local space–time coefficients of a right‐truncated Poisson process. The truncated Poisson space–time autoregressive (TPSTAR) model is motivated by first examining a time‐series model for the entire domain. Then a Poisson generalized linear model is considered that uses grid boxes within the domain and adds offset factors for latitude and longitude. A natural extension is then made that includes instantaneous local and autoregressive coupling between the grids. A final version of the model is found by backward selection of the predictors based on values of Bayesian and Akiake information criteria. The final model has five nearest neighbours and statistically significant couplings. Hindcasts are performed on the hurricane seasons from 1994 to 1997. Results show that, on average, model forecast probabilities are larger in regions in which hurricanes occurred. Quantitative skill assessment indicates some useful skill above climatology—currently the default leading candidate. The TPSTAR model could be a valuable guidance product when issuing seasonal hurricane forecasts. Copyright © 2002 Royal Meteorological Society.

Testing for trend in North Atlantic Hurricane activity, 1900-98

Testing for trend in North Atlantic Hurricane activity, 1900-98

Forecast calls for continued period of active hurricane seasons in the North Atlantic

“I have been designated as a representative of Chicken Little to tell you the sky is falling with regard to hurricanes.” So said William Gray professor of atmospheric science at Colorado State University at a July 26 briefing on Capitol Hill. The briefing, sponsored by the Congressional Natural Hazards Caucus, the (U.S.) University Corporation for Atmospheric Research, and the American Meteorological Society highlighted a new report about the current active hurricane period in the North Atlantic, as well as funding needs for hurricane research. “It is amazing the threat we appear to be in for in the next two to three decades, and how little realization of this [there] is with the government and with the general public,” said Gray a long‐time forecaster of seasonal hurricane activity and co‐author of a July 19 article in Science, “The Recent Increase in Atlantic Hurricane Activity: Causes and Implications.”

The recent increase in Atlantic hurricane activity: causes and implications.

The years 1995 to 2000 experienced the highest level of North Atlantic hurricane activity in the reliable record. Compared with the generally low activity of the previous 24 years (1971 to 1994), the past 6 years have seen a doubling of overall activity for the whole basin, a 2.5-fold increase in major hurricanes (>/=50 meters per second), and a fivefold increase in hurricanes affecting the Caribbean. The greater activity results from simultaneous increases in North Atlantic sea-surface temperatures and decreases in vertical wind shear. Because these changes exhibit a multidecadal time scale, the present high level of hurricane activity is likely to persist for an additional approximately 10 to 40 years. The shift in climate calls for a reevaluation of preparedness and mitigation strategies.

Atlantic basin hurricanes : Indices of climatic changes

Accurate records of basinwide Atlantic and U.S. landfalling hurricanes extend back to the mid 1940s and the turn of the century, respectively, as a result of aircraft reconnaissance and instrumented weather stations along the U.S. coasts. Such long-term records are not exceeded elsewhere in the tropics. The Atlantic hurricanes, U.S. landfalling hurricanes and U.S. normalized damage time series are examined for interannual trends and multidecadal variability. It is found that only weak linear trends can be ascribed to the hurricane activity and that multidecadal variability is more characteristic of the region. Various environmental factors including Caribbean sea level pressures and 200mb zonal winds, the stratospheric Quasi-Biennial Oscillation, the El Nino-Southern Oscillation, African West Sahel rainfall and Atlantic sea surface temperatures, are analyzed for interannual links to the Atlantic hurricane activity. All show significant, concurrent relationships to the frequency, intensity and duration of Atlantic hurricanes. Additionally, variations in the El Nino-Southern Oscillation are significantly linked to changes in U.S. tropical cyclone-caused damages. Finally, much of the multidecadal hurricane activity can be linked to the Atlantic Multidecadal Mode - an empirical orthogonal function pattern derived from a global sea surface temperature record. Such linkages may allow for prediction of Atlantic hurricane activity on a multidecadal basis. These results are placed into the context of climate change and natural hazards policy.

Multi-year prediction model of North Atlantic hurricane activity

An empirical prediction algorithm is developed to assess the potential of useful multi-season forecasts of North Atlantic hurricane activity. The algorithm is based on combining separate univariate autoregressive moving average (ARMA) models for each of three dominant components of hurricane activity. A Bayesian criterion is used to select the order of each model. In a single retroactive hindcast experiment, the algorithm is found to make better hindcasts than an ARMA model of the detrended series. A real-time forecast of hurricane activity for the 1997 North Atlantic hurricane season proves to be more accurate than two competitive single-season forecast models. It is expected that the routine use of the forecast algorithm in an operational setting will result in only marginal skill against climatology; it could however offer considerable forecast value as realized by benefits to decision makers in the reinsurance industry.

Climate Assessment for 1996

The climate of 1996 can be characterized by several phenomena that reflect substantial deviations from the mean state of the atmosphere persisting from months to seasons. First, mature cold-episode conditions persisted across the tropical Pacific from November 1995 through May 1996 and contributed to large-scale anomalies of atmospheric circulation, temperature, and precipitation across the Tropics, the North Pacific and North America. These anomalies were in many respects opposite to those that had prevailed during the past several years in association with a prolonged period of tropical Pacific warm-episode conditions (ENSO). Second, strong tropical intraseasonal (Madden–Julian oscillations) activity was observed during most of the year. The impact of these oscillations on extratropical circulation variability was most evident late in the year in association with strong variations in the eastward extent of the East Asian jet and in the attendant downstream circulation, temperature, and precipitation patterns over the eastern North Pacific and central North America. Third, a return to the strong negative phase of the atmospheric North Atlantic oscillation (NAO) during November 1995–February 1996, following a nearly continuous 15-yr period of positive-phase NAO conditions, played a critical role in affecting temperature and precipitation patterns across the North Atlantic, Eurasia, and northern Africa. The NAO also contributed to a significant decrease in wintertime temperatures across large portions of Siberia and northern Russia from those that had prevailed during much of the 1980s and early 1990s. Other regional aspects of the short-term climate during 1996 included severe drought across the southwestern United States and southern plains states during October 1995–May 1996, flooding in the Pacific Northwest region of the United States during the 1995/96 and 1996/97 winters, a cold and extremely snowy 1995/96 winter in the eastern United States, a second consecutive year of above-normal North Atlantic hurricane activity, near-normal rains in the African Sahel, above-normal rainfall across southeastern Africa during October 1995–April 1996, above-normal precipitation for most of the year across eastern and southeastern Australia following severe drought in these areas during 1995, and generally nearnormal monsoonal rains in India with significantly below-normal rainfall in Bangladesh and western Burma. The global annual mean surface temperature for land and marine areas during 1996 averaged 0.21°C above the 1961–90 base period means. This is a decrease of 0.19°C from the record warm year of 1995 but was still among the 10 highest values observed since 1860. The global land-only temperature for 1996 was 0.06°C above normal and was the lowest anomaly observed since 1985 (−0.11°C). Much of this relative decrease in global temperatures occurred in the Northern Hemisphere extratropics, where land-only temperatures dropped from 0.42°C above normal in 1995 to 0.04°C below normal in 1996. The year also witnessed a continuation of near-record low ozone amounts in the Southern Hemisphere stratosphere, along with an abnormally prolonged appearance of the “ozone hole” into early December. The areal extent of the ozone hole in November and early December exceeded that previously observed for any such period on record. However, its areal extent at peak amplitude during late September–early October was near that observed during the past several years.

Historical Developments Leading to Current Forecast Models of Annual Atlantic Hurricane Activity

There is considerable interest in forecasting interannual hurricane activity for the Atlantic basin. Various predictors representing different components of the tropical Atlantic climate have been suggested. The choice of predictors is based on previous research into contemporaneous and lag relationships with seasonal hurricane and tropical storm frequency. Past research is divided into five distinct periods: the search for physical relationships, the use of composite charts, the use of satellite imagery and climatology of easterly waves, the emergence of recent ideas, and the development of prediction models. As an historical summary this paper describes the important research contributions in each period leading to our current understanding of yearly hurricane variability. The paper concludes by describing current methods for forecasting this variability and recommends an area for future investigations.

Seasonal forecasting of Atlantic hurricane activity

Seasonal forecasting of Atlantic hurricane activity