Identification of Atlantic Basin Tropical Cyclones Affected by Significant Dry Air Events in Total Precipitable Water Imagery (1987-2015)

Total precipitable water (TPW) derived from the Special Sensor Microwave/Imager (SSM/I) is a powerful tool that can be used to better understand the climatological relationship between tropical cyclones (TCs) and dry air. In this study, SSM/I TPW was used to identify and analyze TCs in close proximity to (i.e., within 10° of) significant dry air events (SDAEs), or SDAE-TC encounters. SDAEs must be at least one standard deviation drier than climatology and include Saharan air layers (SALs), mid-latitude dry air intrusions, and dry air hybrids. SSM/I TPW can resolve near-surface moisture, even beneath cirrus clouds, providing critical insight into moisture gradients associated with SDAE-TC encounters. SSM/I TPW was analyzed in the Atlantic basin from 1987-2015 to create a climatological estimate of how often TCs were in close proximity to SDAEs, especially SALs. Of the 381 TCs that formed within the 29-year study period, 125 encountered an SDAE east of 70°W. In most instances, dry air associated with an SDAE did not clearly penetrate into the inner core of the nearby TC, creating uncertainty about whether or not an interaction actually occurred. The average annual SDAE-TC encounter rate was 33% and varied considerably year-to-year (12-60%). For greater than 50% of the SDAE-TC encounters, the TC was named by the National Hurricane Center either that day or the following. SSM/I TPW provides strong evidence that SDAE-TC encounters are an important element in the climatology of Atlantic basin TCs.

Total precipitable water (TPW) derived from the Special Sensor Microwave/Imager (SSM/I) is a powerful tool that can be used to better understand the climatological relationship between tropical cyclones (TCs) and dry air. In this study, SSM/I TPW was used to identify and analyze TCs in close proximity to (i.e., within 10° of) significant dry air events (SDAEs), or SDAE-TC encounters. SDAEs must be at least one standard deviation drier than climatology and include Saharan air layers (SALs), mid-latitude dry air intrusions, and dry air hybrids. SSM/I TPW can resolve near-surface moisture, even beneath cirrus clouds, providing critical insight into moisture gradients associated with SDAE-TC encounters. SSM/I TPW was analyzed in the Atlantic basin from 1987-2015 to create a climatological estimate of how often TCs were in close proximity to SDAEs, especially SALs. Of the 381 TCs that formed within the 29-year study period, 125 encountered an SDAE east of 70°W. In most instances, dry air associated with an SDAE did not clearly penetrate into the inner core of the nearby TC, creating uncertainty about whether or not an interaction actually occurred. The average annual SDAE-TC encounter rate was 33% and varied considerably year-to-year (12-60%). For greater than 50% of the SDAE-TC encounters, the TC was named by the National Hurricane Center either that day or the following. SSM/I TPW provides strong evidence that SDAE-TC encounters are an important element in the climatology of Atlantic basin TCs.