Spatial and Temporal Trends in the Location of the Lifetime Maximum Intensity of Tropical Cyclones
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Abstract:
The climatology of tropical cyclones is an immediate research need, specifically to better understand their long-term patterns and elucidate their future in a changing climate. One important pattern that has recently been detected is the poleward shift of the lifetime maximum intensity (LMI) of tropical cyclones. This study further assessed the recent (1977–2015) spatial changes in the LMI of tropical cyclones, specifically those of tropical storm strength or stronger in the North Atlantic and northern West Pacific basins. Analyses of moving decadal means suggested that LMI locations migrated south in the North Atlantic and north in the West Pacific. In addition to a linear trend, there is a cyclical migration of LMI that is especially apparent in the West Pacific. Relationships between LMI migration and intensity were explored, as well as LMI location relative to landfall. The southerly trend of LMI in the North Atlantic was most prevalent in the strongest storms, resulting in these storms reaching their LMI farther from land. The relationship between intensity and LMI migration in the West Pacific was not as clear, but the most intense storms have been reaching LMI closer to their eventual landfall location. This work adds to those emphasizing the importance of understanding the climatology of the most intense hurricanes and shows there are potential human impacts resulting from any migration of LMI.Keywords:
Landfall
Atlantic hurricane
African easterly jet
Intensity
Lindner, B.L.; Holden, W.; Neuhauser, A., and Evsich, R., 2020. Climatology of tropical cyclone strikes along the southeastern coastline of the United States. Journal of Coastal Research, 36(6), 1162–1177. Coconut Creek (Florida), ISSN 0749-0208.It has been theorized that tropical cyclones originating in or passing through the Gulf of Mexico (hereafter referred to as GOM tropical cyclones) may significantly impact communities along the Atlantic coast of the southeastern United States. To explore this hypothesis, site-specific climatologies were compiled using National Hurricane Center records of tropical cyclones that passed within 139 km of either Savannah, Georgia, or Wilmington, North Carolina, during the years 1851–2018. Return periods for tropical cyclones are longer for Savannah than for Wilmington, particularly for intense hurricanes. Intense GOM hurricanes are weakened by land interaction, which would result in longer return periods. A secondary maximum in the number of tropical storms early in hurricane season is more pronounced with proximity to the Gulf of Mexico, which is again consistent with the contribution from GOM tropical cyclones. Moreover, the percentage of tropical cyclones that passed near Savannah but did not make landfall is higher than that for Wilmington, again an indication of the significance of GOM tropical cyclones. Further evidence of the influence of GOM tropical cyclones is seen in the difference in approach angle and translational velocity between tropical storms and hurricanes. In addition, translational velocities for tropical cyclones increase with latitude, and translational velocities for tropical cyclones near either Savannah or Wilmington increase as the hurricane season progresses. Both relationships are likely due to the interaction of tropical cyclones with synoptic and planetary-scale winds. The median date for tropical cyclones has shifted earlier in recent decades for both Savannah and Wilmington, which is potentially an indication of climate change. An improved understanding of the climatology of tropical cyclones could lead to enhanced city planning, building codes, infrastructure, and resource management.
Atlantic hurricane
African easterly jet
Tropical cyclone scales
Tropical cyclogenesis
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Abstract The automatic tracking technique used by Thorncroft and Hodges has been used to identify coherent vorticity structures at 850 hPa over West Africa and the tropical Atlantic in the 40-yr ECMWF Re-Analysis. The presence of two dominant source regions, north and south of 15°N over West Africa, for storm tracks over the Atlantic was confirmed. Results show that the southern storm track provides most of the storms that reach the main development region where most tropical cyclones develop. There exists marked seasonal variability in location and intensity of the storms leaving the West African coast, which may influence the likelihood of downstream intensification and longevity. There exists considerable year-to-year variability in the number of West African storm tracks, both in numbers over the land and continuing out over the tropical Atlantic Ocean. While the low-frequency variability is well correlated with Atlantic tropical cyclone activity, West African rainfall, and SSTs, the interannual variability is found to be uncorrelated with these. In contrast, variance of the 2–6-day-filtered meridional wind, which provides a synoptic-scale measure of African easterly wave activity, shows a significant, positive correlation with tropical cyclone activity at interannual time scales.
African easterly jet
Atlantic hurricane
Extratropical cyclone
Tropical Atlantic
Cyclogenesis
Tropical cyclone scales
Storm track
Tropical cyclogenesis
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The 1991 hurricane season in the Atlantic basin featured 73 tropical waves (also known as African waves), most of which were relatively weak. These waves generated fewer than normal Atlantic tropical cyclones: seven tropical depressions, of which only three intensified into tropical storms. Remarkably, none of these systems became hurricanes. The remainder of the Atlantic tropical cyclones formed from other sources. African waves triggered nearly all of the eastern Pacific tropical cyclones in 1991.
Atlantic hurricane
African easterly jet
Tropical Atlantic
Tropical cyclone scales
Tropical cyclogenesis
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The 1991 hurricane season produced 76 tropical waves of which 12 became tropical depressions. African seedlings initiated 10 of the 14 named Atlantic storms and all of the eastern Pacific tropical cyclones. A comparison with previous years is presented.
Atlantic hurricane
African easterly jet
Tropical Atlantic
Tropical cyclone scales
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A total of 62 and 63 tropical waves were counted in the Atlantic from May to November during 1996 and 1997, respectively. These waves led to the formation of 12 of the 13 total number of tropical cyclones in 1996 and only 3 of 7 tropical cyclones in 1997. All of the tropical depressions became tropical storms in 1996 and only one failed to become a named storm in 1997. On average, 62% of the Atlantic tropical depressions develop from tropical waves. These waves contributed to the formation of 92% of the eastern Pacific tropical cyclones in 1996 and 83% in 1997. Tropical waves and their environment during the 1996 and 1997 seasons are discussed.
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Tropical Atlantic
Atlantic hurricane
Tropical cyclogenesis
Tropical cyclone scales
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A total of 69 tropical waves (also known as African and easterly waves) were counted in the Atlantic basin during the 1992 hurricane season. As was the case in 1991, the waves were, in general, relatively weak. These waves led to the formation of only four tropical depressions in the Atlantic hurricane basin, of which one intensified into a tropical storm and another intensified into Hurricane Andrew. Andrew was the only 1992 Atlantic hurricane to originate from a tropical wave. There were five additional tropical depressions that were primarily initiated by systems of nontropical origin. These produced three hurricanes and one tropical storm. It appears that tropical waves led to the formation of practically all of the eastern Pacific tropical cyclones in 1992.
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African easterly jet
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A total of 70 tropical waves (also known as African or easterly waves) were counted in the Atlantic basin during the 1993 hurricane season. These waves led to the formation of 9 of the 10 total number of tropical cyclones in the Atlantic hurricane basin. It appears that tropical waves led to the formation of practically all of the eastern Pacific tropical cyclones in 1993.
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African easterly jet
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Tropical cyclogenesis
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Abstract Atlantic tropical cyclone (TC) genesis is strongly linked with African easterly waves (AEWs) on the synoptic time scale. However, the TC‐AEW relationship is unclear on interannual to climate time scales, and it is unknown whether AEWs are necessary to maintain climatological TC frequency, that is, whether TCs are limited by AEWs. We investigated the impact of AEW suppression on seasonal Atlantic TC activity using a 10‐member ensemble of regional climate model simulations in which AEWs were either prescribed or removed through the lateral boundary condition. The climate model experiments produced no significant change in seasonal Atlantic TC number, indicating that AEWs are not necessary to maintain climatological basin‐wide TC frequency even though TCs readily originate from these types of disturbances. This suggests that the specific type of “seedling” disturbance is unimportant for determining basin‐wide seasonal Atlantic TC number and that in the absence of AEWs, TCs will generate by other mechanisms. The results imply that changes in the presence of AEWs may not be reliable predictors of seasonal variability and future change in Atlantic TC frequency.
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Tropical Atlantic
Atlantic hurricane
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The interannual variability of outgoing longwave radiation (OLR) over Africa from the Advanced Very High Resolution Radiometer (AVHRR) and zonal wind speed in the African easterly jet (AEJ) is analyzed and discussed in the context of Atlantic tropical cyclone activity. It is found that hurricane and tropical storm totals in the Atlantic basin are closely related to the African meridional OLR contrast (AMOC). It is suggested that the AMOC provides a simple yet novel way to simultaneously characterize the meridional temperature gradient and ITCZ activity, both of which play integral roles in generating African easterly waves. Complimentary to observed relationships between Sahel rainfall and Atlantic tropical cyclone activity, the potential for the AMOC to augment existing techniques used in preparing Atlantic hurricane season outlooks is also discussed.
African easterly jet
Atlantic hurricane
Intertropical Convergence Zone
Tropical cyclogenesis
Tropical Atlantic
Tropical cyclone scales
Predictability
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The assumption that tropical cyclones respond primarily to sea surface temperatures (SSTs) local to their main development regions underlies much of the concern regarding the possible impacts of anthropogenic greenhouse warming on tropical cyclone statistics. Here the observed relationship between changes in sea surface temperature and tropical cyclone intensities in the Atlantic basin is explored. Atlantic tropical cyclone intensity fluctuations and storm numbers are shown to depend not only upon SST anomalies local to the Atlantic main development region, but also in a negative sense upon the tropical mean SST. This behavior is shown in part to be consistent with changes in the tropical cyclone potential intensity that provides an upper bound on storm intensity. However, Atlantic tropical cyclone intensity fluctuations are more nonlocal than the potential intensity itself and specifically vary along with Atlantic main development region SST anomalies relative to the tropical mean SST. This suggests that there is no straightforward link between warmer SSTs in the main development region and more intense tropical cyclones.
Atlantic hurricane
Tropical cyclogenesis
Tropical cyclone scales
African easterly jet
Tropical Atlantic
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