Strong association between west african rainfall and u.s. Landfall of intense hurricanes

Tropical Atlantic multidecadal variability is dominated by external forcing

The tropical Atlantic climate is characterized by prominent and correlated multidecadal variability in Atlantic sea surface temperatures (SSTs), Sahel rainfall and hurricane activity1-4. Owing to uncertainties in both the models and the observations, the origin of the physical relationships among these systems has remained controversial3-7. Here we show that the cross-equatorial gradient in tropical Atlantic SSTs-largely driven by radiative perturbations associated with anthropogenic emissions and volcanic aerosols since 19503,7-is a key determinant of Atlantic hurricane formation and Sahel rainfall. The relationship is obscured in a large ensemble of CMIP6 Earth system models, because the models overestimate long-term trends for warming in the Northern Hemisphere relative to the Southern Hemisphere from around 1950 as well as associated changes in atmospheric circulation and rainfall. When the overestimated trends are removed, correlations between SSTs and Atlantic hurricane formation and Sahel rainfall emerge as a response to radiative forcing, especially since 1950 when anthropogenic aerosol forcing has been high. Our findings establish that the tropical Atlantic SST gradient is a stronger determinant of tropical impacts than SSTs across the entire North Atlantic, because the gradient is more physically connected to tropical impacts via local atmospheric circulations8. Our findings highlight that Atlantic hurricane activity and Sahel rainfall variations can be predicted from radiative forcing driven by anthropogenic emissions and volcanism, but firmer predictions are limited by the signal-to-noise paradox9-11 and uncertainty in future climate forcings.

Predicting Atlantic Hurricanes Using Machine Learning

Every year, tropical hurricanes affect North and Central American wildlife and people. The ability to forecast hurricanes is essential in order to minimize the risks and vulnerabilities in North and Central America. Machine learning is a newly tool that has been applied to make predictions about different phenomena. We present an original framework utilizing Machine Learning with the purpose of developing models that give insights into the complex relationship between the land–atmosphere–ocean system and tropical hurricanes. We study the activity variations in each Atlantic hurricane category as tabulated and classified by NOAA from 1950 to 2021. By applying wavelet analysis, we find that category 2–4 hurricanes formed during the positive phase of the quasi-quinquennial oscillation. In addition, our wavelet analyses show that super Atlantic hurricanes of category 5 strength were formed only during the positive phase of the decadal oscillation. The patterns obtained for each Atlantic hurricane category, clustered historical hurricane records in high and null tropical hurricane activity seasons. Using the observational patterns obtained by wavelet analysis, we created a long-term probabilistic Bayesian Machine Learning forecast for each of the Atlantic hurricane categories. Our results imply that if all such natural activity patterns and the tendencies for Atlantic hurricanes continue and persist, the next groups of hurricanes over the Atlantic basin will begin between 2023 ± 1 and 2025 ± 1, 2023 ± 1 and 2025 ± 1, 2025 ± 1 and 2028 ± 1, 2026 ± 2 and 2031 ± 3, for hurricane strength categories 2 to 5, respectively. Our results further point out that in the case of the super hurricanes of the Atlantic of category 5, they develop in five geographic areas with hot deep waters that are rather very well defined: (I) the east coast of the United States, (II) the Northeast of Mexico, (III) the Caribbean Sea, (IV) the Central American coast, and (V) the north of the Greater Antilles.

North Atlantic Hurricane Winds in Warmer than Normal Seas

Tropical cyclones devastate coastlines around the world. The United States and surrounding areas experienced catastrophic extreme events in recent hurricane seasons. Understanding extreme hurricanes and how they change in a warming ocean environment is of the utmost importance. This study makes use of the historical, positive relationship between average summer sea surface temperatures (SSTs) and maximum hurricane wind speeds across the North Atlantic Basin from 1854–2018. Geographically weighted regression shows how the relationship between hurricane winds and SSTs varies across space. Each localized slope is used to increase historical wind speeds to represent winds in a three-degree Celsius warmer-than-average sea surface. The winds are then used to estimate the maximum intensity of the thirty-year hurricane (one with a 3.3% annual probability of occurrence) across the hexagonal grid using extreme value statistics. Viewing the results spatially allows for geographic patterns to emerge in the overall risk of major hurricane occurrence in warm SST environments. This study showcases the difference in the historical extreme compared to the potential future extreme in the hopes to better inform those charged with making important, life-saving decisions along the U.S. and neighboring coasts.

The role of Atlantic overturning circulation in the recent decline of Atlantic major hurricane frequency

Observed Atlantic major hurricane frequency has exhibited pronounced multidecadal variability since the 1940s. However, the cause of this variability is debated. Using observations and a coupled earth system model (GFDL-ESM2G), here we show that the decline of the Atlantic major hurricane frequency during 2005–2015 is associated with a weakening of the Atlantic Meridional Overturning Circulation (AMOC) inferred from ocean observations. Directly observed North Atlantic sulfate aerosol optical depth has not increased (but shows a modest decline) over this period, suggesting the decline of the Atlantic major hurricane frequency during 2005–2015 is not likely due to recent changes in anthropogenic sulfate aerosols. Instead, we find coherent multidecadal variations involving the inferred AMOC and Atlantic major hurricane frequency, along with indices of Atlantic Multidecadal Variability and inverted vertical wind shear. Our results provide evidence for an important role of the AMOC in the recent decline of Atlantic major hurricane frequency.

The reason for the decline in frequency of Atlantic major hurricanes since 2005 is still debated. Here the authors combine observations with model simulations to show that this decline is largely due to changes in the Atlantic ocean meridional overturning circulation.

Atlantic hurricane surge response to geoengineering

Devastating floods due to Atlantic hurricanes are relatively rare events. However, the frequency of the most intense storms is likely to increase with rises in sea surface temperatures. Geoengineering by stratospheric sulfate aerosol injection cools the tropics relative to the polar regions, including the hurricane Main Development Region in the Atlantic, suggesting that geoengineering may mitigate hurricanes. We examine this hypothesis using eight earth system model simulations of climate under the Geoengineering Model Intercomparison Project (GeoMIP) G3 and G4 schemes that use stratospheric aerosols to reduce the radiative forcing under the Representative Concentration Pathway (RCP) 4.5 scenario. Global mean temperature increases are greatly ameliorated by geoengineering, and tropical temperature increases are at most half of those temperature increases in the RCP4.5. However, sulfate injection would have to double (to nearly 10 teragrams of SO2 per year) between 2020 and 2070 to balance the RCP4.5, approximately the equivalent of a 1991 Pinatubo eruption every 2 y, with consequent implications for stratospheric ozone. We project changes in storm frequencies using a temperature-dependent generalized extreme value statistical model calibrated by historical storm surges and observed temperatures since 1923. The number of storm surge events as big as the one caused by the 2005 Katrina hurricane are reduced by about 50% compared with no geoengineering, but this reduction is only marginally statistically significant. Nevertheless, when sea level rise differences in 2070 between the RCP4.5 and geoengineering are factored into coastal flood risk, we find that expected flood levels are reduced by about 40 cm for 5-y events and about halved for 50-y surges.

An ENSO-Forecast Independent Statistical Model for the Prediction of Annual Atlantic Tropical Cyclone Frequency in April

Statistical models for preseason prediction of annual Atlantic tropical cyclone (TC) and hurricane counts generally include El Niño/Southern Oscillation (ENSO) forecasts as a predictor. As a result, the predictions from such models are often contaminated by the errors in ENSO forecasts. In this study, it is found that the latent heat flux (LHF) over Eastern Tropical Pacific (ETP, defined as the region 0°–5°N, 115°–125°W) in spring is negatively correlated with the annual Atlantic TC and hurricane counts. By using stepwise backward elimination regression, it is further shown that the March value of ETP LHF is a better predictor than the spring or summer ENSO index for Atlantic TC counts. Leave-one-out cross validation indicates that the annual Atlantic TC counts predicted by this ENSO-independent statistical model show a remarkable correlation with the actual TC counts (R=0.72;Pvalue<0.01). For Atlantic hurricanes, the predictions using March ETP LHF and summer (July–September) ENSO indices show only minor differences except in moderate to strong El Niño years. Thus, March ETP LHF is an excellent predictor for seasonal Atlantic TC prediction and a viable alternative to using ENSO index for Atlantic hurricane prediction.

Projected Atlantic hurricane surge threat from rising temperatures

Detection and attribution of past changes in cyclone activity are hampered by biased cyclone records due to changes in observational capabilities. Here, we relate a homogeneous record of Atlantic tropical cyclone activity based on storm surge statistics from tide gauges to changes in global temperature patterns. We examine 10 competing hypotheses using nonstationary generalized extreme value analysis with different predictors (North Atlantic Oscillation, Southern Oscillation, Pacific Decadal Oscillation, Sahel rainfall, Quasi-Biennial Oscillation, radiative forcing, Main Development Region temperatures and its anomaly, global temperatures, and gridded temperatures). We find that gridded temperatures, Main Development Region, and global average temperature explain the observations best. The most extreme events are especially sensitive to temperature changes, and we estimate a doubling of Katrina magnitude events associated with the warming over the 20th century. The increased risk depends on the spatial distribution of the temperature rise with highest sensitivity from tropical Atlantic, Central America, and the Indian Ocean. Statistically downscaling 21st century warming patterns from six climate models results in a twofold to sevenfold increase in the frequency of Katrina magnitude events for a 1 °C rise in global temperature (using BNU-ESM, BCC-CSM-1.1, CanESM2, HadGEM2-ES, INM-CM4, and NorESM1-M).

Homogeneous record of Atlantic hurricane surge threat since 1923

Detection and attribution of past changes in cyclone activity are hampered by biased cyclone records due to changes in observational capabilities. Here we construct an independent record of Atlantic tropical cyclone activity on the basis of storm surge statistics from tide gauges. We demonstrate that the major events in our surge index record can be attributed to landfalling tropical cyclones; these events also correspond with the most economically damaging Atlantic cyclones. We find that warm years in general were more active in all cyclone size ranges than cold years. The largest cyclones are most affected by warmer conditions and we detect a statistically significant trend in the frequency of large surge events (roughly corresponding to tropical storm size) since 1923. In particular, we estimate that Katrina-magnitude events have been twice as frequent in warm years compared with cold years (P < 0.02).

Effects of marsh pond terracing on coastal wintering waterbirds before and after Hurricane Rita

From February to March 2005-2006, we surveyed wintering waterbirds to test effects of terracing on coastal pond use before and after Hurricane Rita. Marsh terracing is intended to slow coastal marsh loss in the Chenier Plain by slowing marsh erosion and encouraging vegetation expansion. Terraces also increase marsh edge in ponds, possibly benefiting waterbirds. We monitored paired terraced and unterraced ponds in three sites within southwestern Louisiana's Chenier Plain. Waterbirds were 75% more numerous in terraced than unterraced ponds. Waterbird richness was similar among ponds when corrected for number of individuals, suggesting terracing increased bird density but did not provide habitat unique from unterraced ponds. Birds were 93% more numerous following Hurricane Rita, mostly due to an influx of migrating waterfowl. Year round residents were similar in number before and after Hurricane Rita. Resident richness did not differ among years after correcting for number of observed individuals. Wading and dabbling foragers were more abundant in terraced ponds and these two guilds represented 74% of birds observed. We detected no difference among ponds for other guilds, i.e., probing, aerial, and diving foragers. Increasing proportion of mash edge increased bird density disproportionately: On average ponds with 10% edge had 6 birds observed and ponds with 30% edge had 16 birds observed. Terraces increased habitat interspersion and were an effective tool for increasing numbers of wintering waterfowl and wading birds. The extent to which terraces were sustainable following hurricane forces is unknown.

A catastrophic death assemblage and paleoclimatic implications of pliocene seabirds of Florida

A deposit of fossil seabirds from the late Pliocene of Florida includes more than 130 skeletons of an extinct cormorant that is related phylogenetically to Recent species currently restricted to the eastern north Pacific. Evidence suggests the birds died in a single catastrophic event, perhaps a red tide. The fossil cormorant, along with other extinct seabirds and marine mammals, supports molluscan evidence for cold-water upwelling along the Florida Gulf Coast during the Pliocene. A decline in species richness of marine vertebrates throughout the Pliocene of Florida coincides with cessation of upwelling after emergences of the Panamanian Land Bridge.

Heightened tropical cyclone activity in the North Atlantic: natural variability or climate trend?

We find that long-period variations in tropical cyclone and hurricane frequency over the past century in the North Atlantic Ocean have occurred as three relatively stable regimes separated by sharp transitions. Each regime has seen 50% more cyclones and hurricanes than the previous regime and is associated with a distinct range of sea surface temperatures (SSTs) in the eastern Atlantic Ocean. Overall, there appears to have been a substantial 100-year trend leading to related increases of over 0.7 degrees C in SST and over 100% in tropical cyclone and hurricane numbers. It is concluded that the overall trend in SSTs, and tropical cyclone and hurricane numbers is substantially influenced by greenhouse warming. Superimposed on the evolving tropical cyclone and hurricane climatology is a completely independent oscillation manifested in the proportions of tropical cyclones that become major and minor hurricanes. This characteristic has no distinguishable net trend and appears to be associated with concomitant variations in the proportion of equatorial and higher latitude hurricane developments, perhaps arising from internal oscillations of the climate system. The period of enhanced major hurricane activity during 1945-1964 is consistent with a peak period in major hurricane proportions.

Some aspects of ecophysiological and biogeochemical responses of tropical forests to atmospheric change

Atmospheric changes that may affect physiological and biogeochemical processes in old-growth tropical forests include: (i) rising atmospheric CO2 concentration; (ii) an increase in land surface temperature; (iii) changes in precipitation and ecosystem moisture status; and (iv) altered disturbance regimes. Elevated CO2 is likely to directly influence numerous leaf-level physiological processes, but whether these changes are ultimately reflected in altered ecosystem carbon storage is unclear. The net primary productivity (NPP) response of old-growth tropical forests to elevated CO2 is unknown, but unlikely to exceed the maximum experimentally measured 25% increase in NPP with a doubling of atmospheric CO2 from pre-industrial levels. In addition, evolutionary constraints exhibited by tropical plants adapted to low CO2 levels during most of the Late Pleistocene, may result in little response to increased carbon availability. To set a maximum potential response for a Central Amazon forest, using an individual-tree-based carbon cycling model, a modelling experiment was performed constituting a 25% increase in tree growth rate, linked to the known and expected increase in atmospheric CO2. Results demonstrated a maximum carbon sequestration rate of ca. 0.2 Mg C per hectare per year (ha(-1) yr(-1), where 1 ha = 10(4) m2), and a sequestration rate of only 0.05 Mg C ha(-1) yr(-1) for an interval centred on calendar years 1980-2020. This low rate results from slow growing trees and the long residence time of carbon in woody tissues. By contrast, changes in disturbance frequency, precipitation patterns and other environmental factors can cause marked and relatively rapid shifts in ecosystem carbon storage. It is our view that observed changes in tropical forest inventory plots over the past few decades is more probably being driven by changes in disturbance or other environmental factors, than by a response to elevated CO2. Whether these observed changes in tropical forests are the beginning of long-term permanent shifts or a transient response is uncertain and remains an important research priority.

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.

Eight centuries of north atlantic ocean atmosphere variability

Climate in the tropical North Atlantic is controlled largely by variations in the strength of the trade winds, the position of the Intertropical Convergence Zone, and sea surface temperatures. A high-resolution study of Caribbean sediments provides a subdecadally resolved record of tropical upwelling and trade wind variability spanning the past 825 years. These results confirm the importance of a decadal (12- to 13-year) mode of Atlantic variability believed to be driven by coupled tropical ocean-atmosphere dynamics. Although a well-defined interdecadal mode of variability does not appear to be characteristic of the tropical Atlantic, there is evidence that century-scale variability is substantial. The tropical Atlantic may also have been involved in a major shift in Northern Hemisphere climate variability that took place about 700 years ago.

Disaster medical assistance teams: providing health care to a community struck by Hurricane Iniki

STUDY OBJECTIVE

To describe the type of medical care that disaster medical assistance teams (DMATs) provided to a community struck by a major hurricane.

STUDY DESIGN

A prospective study describing the use of DMAT field clinics by a population affected by a major hurricane. Data regarding the type of medical care provided to disaster victims and the acuity of each patient's medical condition were abstracted from medical charts at each field clinic.

SETTING

Three DMAT field clinics that provided medical care to residents of Kauai, Hawaii, after Hurricane Iniki struck the island on September 11, 1992.

RESULTS

From September 16 to 19, 1992, three DMATs provided medical care to 614 people. The patients' average age was 34 years, and 60% were male. The largest treatment categories were injury (40.4%), illness (38.6%), and preventive services (9.0%). Most illnesses and injuries were minor, and 99% of the patients were ambulatory. Only 33 patients (5.4%) were referred to another medical provider. Referrals were generally for procedures not available in DMAT field clinics rather than for life-threatening conditions.

CONCLUSION

DMATs sent to assist with the medical needs of a US community struck by a major hurricane should be prepared to deliver basic medical services and primary health care. The need for these medical services will continue beyond the impact phase of a hurricane disaster.