Atlantic Major Hurricane Research Articles

Changes in Atlantic major hurricane frequency since the late-19th century

Atlantic hurricanes are a major hazard to life and property, and a topic of intense scientific interest. Historical changes in observing practices limit the utility of century-scale records of Atlantic major hurricane frequency. To evaluate past changes in frequency, we have here developed a homogenization method for Atlantic hurricane and major hurricane frequency over 1851–2019. We find that recorded century-scale increases in Atlantic hurricane and major hurricane frequency, and associated decrease in USA hurricanes strike fraction, are consistent with changes in observing practices and not likely a true climate trend. After homogenization, increases in basin-wide hurricane and major hurricane activity since the 1970s are not part of a century-scale increase, but a recovery from a deep minimum in the 1960s–1980s. We suggest internal (e.g., Atlantic multidecadal) climate variability and aerosol-induced mid-to-late-20th century major hurricane frequency reductions have probably masked century-scale greenhouse-gas warming contributions to North Atlantic major hurricane frequency.

Heavier Inner-core Rainfall of Major Hurricanes in the North Atlantic Basin than Other Global Basins

AbstractBased on 19 years of precipitation data collected by the Tropical Rainfall Measuring Mission (TRMM) and the Global Precipitation Measurement (GPM) mission, a comparison of the rainfall produced by tropical cyclones (TCs) in different global basins is presented. A total of 1789 TCs were examined in the period from 1998 to 2016 by taking advantage of more than 47,737 observations of TRMM/GPM 3B42 multi-satellite derived rainfall amounts. The axisymmetric component of the TC rainfall is analyzed in all TC-prone basins. The resulting radial profiles show that major hurricanes in the Atlantic basin exhibit significantly heavier inner-core rainfall rates than those in any other basins. To explain the possible causes of this difference, rainfall distributions for major hurricanes are stratified according to different TC intensity and environmental variables. Based on the examination of these parameters, we found that the stronger rainfall rates in the Atlantic major hurricanes are associated with higher values of convective available potential energy, drier relative humidity in the low to middle troposphere, colder air temperature at 250hPa, and stronger vertical wind shear than other basins. These results have important implications in the refining of our understanding of the mechanisms of TC rainfall.

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 Arbitrary Definition of the Current Atlantic Major Hurricane Landfall Drought

Abstract A major hurricane [96+ knots (kt; 1 kt = 0.51 m s–1) of maximum sustained wind] has not made landfall in the United States since Wilma (2005). Recent elegant stochastic–statistical modeling estimates the return period of a 9-yr streak for this metric as 177 yr, suggesting extraordinary rarity, especially in the context of the length of the record (1851–2014). Current awareness of the drought is increased given that the 2015 hurricane season is expected to be suppressed from El Niño and the recent anniversaries of several noteworthy landfalls. Yet, here we show that the significance or even existence of the current 9-yr drought is highly dependent on the metric used. Acknowledging that wind intensity estimates are binned every 5 kt and have approximate 10-kt uncertainty, we examine the same record using landfall thresholds of 95–105 kt. Using 105-kt landfall, 1993–2003 becomes a previously unreported yet more remarkable 11-yr drought and 1981–88 becomes an 8-yr drought. Further, landfall minimum sea level pressure is more reliably estimated than maximum sustained wind speed. For landfall intensities stronger than 960 hPa (a climatological threshold for 100 kt), the current drought disappears because of Irene (2011) and Sandy (2012). A coastline-independent yet nearby proximity metric is tested and reveals a nonexistent drought. Accordingly, this study suggests the following: 1) Caution is advised when identifying a hurricane drought and its historical significance. 2) Using hurricane landfall statistics to infer a climate signal is fraught with issues (threshold, coastline, and potentially nonscientific contributions), regardless of intensity metric. 3) From a societal context, human and financial losses matter most, and Irene [2011; $8 billion (U.S. dollars)] and Sandy (2012; $88 billion) occurred during the current drought.

The Tropical Cyclone Diurnal Cycle of Mature Hurricanes

Abstract The diurnal cycle of tropical convection and the tropical cyclone (TC) cirrus canopy has been described extensively in previous studies. However, a complete understanding of the TC diurnal cycle remains elusive and is an area of ongoing research. This work describes a new technique that uses infrared satellite image differencing to examine the evolution of the TC diurnal cycle for all North Atlantic major hurricanes from 2001 to 2010. The imagery reveals cyclical pulses in the infrared cloud field that regularly propagate radially outward from the storm. These diurnal pulses begin forming in the storm’s inner core near the time of sunset each day and continue to move away from the storm overnight, reaching areas several hundreds of kilometers from the circulation center by the following afternoon. A marked warming of the cloud tops occurs behind this propagating feature and there can be pronounced structural changes to a storm as it moves away from the inner core. This suggests that the TC diurnal cycle may be an important element of TC dynamics and may have relevance to TC structure and intensity change. Evidence is also presented showing the existence of statistically significant diurnal signals in TC wind radii and objective Dvorak satellite-based intensity estimates for the 10-yr hurricane dataset that was examined. Findings indicate that TC diurnal pulses are a distinguishing characteristic of the TC diurnal cycle and the repeatability of TC diurnal pulsing in time and space suggests that it may be an unrealized, yet fundamental TC process.

Is recent major hurricane activity normal?

The anomaly of the recent increase in Atlantic major hurricane activity (MHA) is controversial. From a reconstruction of past MHA, Nyberg et al. conclude that the present activity is not unusual by comparison with that of the past 270 years. However, here I estimate the uncertainty of average MHA in the hurricane record before 1945 and show that the reconstruction of Nyberg et al. differs strongly from that record, and probably overestimates past MHA. Owing to this and further reasons, I question whether their reconstruction provides an accurate basis for conclusions about past MHA.

Nyberg et al. reply

Replying to: U. Neu , 10.1038/nature06576 (2008). Neu1 suggests that the reconstruction of Atlantic major hurricane activity (MHA) (that is, frequency) in Nyberg et al.2 overestimates past MHA because it differs significantly from the known observational records of tropical storms and MHA3 before 1945 and overestimates the influence of vertical windshear |Vz|.

Atlantic Major Hurricanes, 1995–2005—Characteristics Based on Best-Track, Aircraft, and IR Images

Abstract The Atlantic major hurricanes during the period of 1995–2005 are examined using best-track data, aircraft-based observations of central pressure, and infrared (IR) satellite images. There were 45 Atlantic major hurricanes (Saffir–Simpson category 3 or higher) during this 11-yr period, which is well above the long-term average. Descriptive statistics (e.g., average, variability, and range) of various characteristics are presented, including intensity, intensification rate, major hurricane duration, location, storm motion, size, and landfall observations. IR images are shown along with IR-derived quantities such as the digital Dvorak technique intensity and IR-defined cold cloud areas. In addition to the satellite intensity estimates, the associated component IR temperatures are documented. A pressure–wind relationship is evaluated, and the deviations of maximum intensity measurements from the pressure–wind relationship are discussed. The Atlantic major hurricane activity of the 1995–2005 period distinctly exceeds the long-term average; however, the average location where major hurricanes reach maximum intensity has not changed. The maximum intensity for each 1995–2005 Atlantic major hurricane is given both as the highest maximum surface wind (Vmax) and the lowest minimum sea level pressure (MSLP). Comparisons are made to other Atlantic major hurricanes with low MSLP back to 1950. Maximum 24-h intensification rates average 21.1 m s−1 day−1 and range up to 48.8 m s−1 day−1 in terms of Vmax. The largest 24-h MSLP decreases average 34.2 hPa and range from 15 to 97 hPa. Major hurricane duration averages 2.7 days with a maximum of 10 days. Hurricane size, as given by the average radius of gale force wind at maximum intensity, averages 250.8 km and has an extremely large range from 92.5 to 427.4 km.

North Atlantic decadal variability and the formation of tropical storms and hurricanes

Both the annual number of Atlantic tropical storms forming south of 23.5°N and of Atlantic major hurricanes increased between the 1970's/1980's and 1995–2000. These increases are coincident with a multi‐decadal warming in North Atlantic SST suggesting that the high activity of 1995–2000 may persist for the next ∼10 to 40 years. However, during 1950–2000 strong decadal oscillations are superimposed on the multi‐decadal changes in both SST and tropical storms (positive SST anomalies, increased storm activity). We appear to be entering a negative phase of the decadal SST signal implying that tropical storm, and most likely major hurricane, activity may be reduced in the next several years rather than remain at the very high 1995–2000 level when both signals were in their positive phase. Tropical storm activity during 2001 and 2002 is less than the expected only from the multi‐decadal signal but for 2002 the main cause may be El Niño.

Comment on “Changes in the rates of North Atlantic major hurricane activity during the 20th century”

Atlantic major hurricanes have a profound impact on human and natural environments. Understanding and predicting these storms’ occurrence on daily, intraseasonal, interannual, multidecadal and climatic timescales can be of tremendous benefit and should be pursued vigorously. Elsner et al. [2000] (hereafter as EJN) address multidecadal changes of Atlantic basin major hurricanes - those tropical cyclones with maximum sustained surface winds of at least 50 m/s. However, aspects of EJN analysis are questionable because its treatment of the Atlantic major hurricane database may be erroneous, because its proposed link to the North Atlantic Oscillation is unsubstantiated, and because it fails to cite or acknowledge key earlier studies. Treating the record of Atlantic major hurricanes since 1900 as trustworthy in its entirety is very questionable. The assumption that the records of major hurricane activity are complete before the advent of aircraft reconnaissance leads directly to the erroneous conclusion that major hurricanes became much more numerous starting in 1943. That year - not coincidentally - was the beginning of routine aircraft flights into hurricanes [Sumner 1944]. EJN state that “the observational bias is smallest for the strong storms considered here”. It is unclear how the authors come to this conclusion. Major hurricanes typically stay at that intensity for an average of 2-3 days and have their 50 m/s or higher winds concentrated in the mesoscale (10s of km) eyewall [Landsea 1993; Powell and Houston 1998]. Before aircraft and satellite reconnaissance, it was simply not possible to detect such small transient features offshore consistently or reliably. Holland [1981] demonstrated that even when numerous ships and buoys are in a strong tropical cyclone, the actual intensity is likely to be drastically underestimated without aircraft or satellite data. Another way to understand the problem is a comparison of the relationship between all major hurricanes to the subset that have hit the United States. (The latter should be sampled adequately back to the beginning of the 20th Century.) These two records are correlated at r=0.41 for the years 1943-99 (less than 17% of the variance) versus r=0.78 for 1900-1942 (over 61% of the variance). (These two correlation coefficients show a strong significant difference in a two-tailed test with a p-value of less than 0.03.) Since in nature the relationship should be relatively steady over time, one can conclude that before the mid-1940s, the Atlantic major hurricane records were less likely to include those that did not strike the United States. Solow and Moore [2000] come to similar conclusions as stated above by analyzing the ratio of landfalling U.S. hurricanes to all Atlantic basin hur

Reply to “Comment on changes in the rates of North Atlantic major hurricane activity during the 20th century”

Reply to “Comment on changes in the rates of North Atlantic major hurricane activity during the 20th century”

Changes in the rates of North Atlantic major hurricane activity during the 20th century

The authors document and explain changes in the rates of North Atlantic major hurricanes over the 20th century. A change‐point analyses identifies two contrasting regimes of activity. The regimes have significantly different occurrence rates that coincide with changes in the climate over the extratropical North Atlantic. In conjunction with the recent Arctic warming and a relaxation of the North Atlantic oscillation, it is speculated that we are beginning a new period of greater major hurricane activity.

Physical Mechanisms for the Association of El Niño and West African Rainfall with Atlantic Major Hurricane Activity

Abstract Physical mechanisms responsible for the contemporaneous association, shown in earlier studies, of North Atlantic basin major hurricane (MH) activity with western Sahelian monsoon rainfall and an equatorial eastern Pacific sea surface temperature index of El Nino are examined, using correlations with 200- and 700-mb level wind data for the period 1968–92. The use of partial correlations isolates some of the relationships associated with the various parameters. The results support previous suggestions that the upper- and lower-level winds over the region in the basin between ∼10° and 20°N where most MHs begin developing are critical determinants of the MH activity in each hurricane season. In particular, interannual fluctuations in the winds that produce changes in the magnitude of vertical shear are one of the most important factors, with reduced shear being associated with increased activity and stronger shear with decreased activity. The results show that most of these critical wind fluctuations...