Impact of Environmental Moisture for TC Genesis from AEWs

Analysis of developing and non-developing AEWs from 2012-2014 will be presented to show the influence of low-level environmental moisture to the northwest of AEW troughs on any associated TC genesis over the eastern Atlantic.   This presentation will use the composite results of Brammer & Thorncroft (2015) as a basis to study individual developing and non-developing AEW troughs.  Utilising the in-situ observations from the NASA Hurricane and Severe Storm Sentinel (HS3) field program with reanalysis fields and kinematic trajectories the influence of both low-level moist and dry air will be shown with respect to TC genesis.

The composite results of Brammer & Thorncroft (2015) have shown that developing AEWs have significantly higher moisture content in the lower troposphere to the northwest of the trough as they exit the African coast compared to favourable non-developing waves. Trajectory analysis revealed that as the AEWs transit over the West African coast the troughs are typically open to the environment to the west and northwest of the trough. For developing waves this means that moist air is ingested into the lower levels of the system, while for non-developing waves dry air was ingested. At this point in the AEW lifecycle the environment northwest of the trough may be fundamental in determining whether a wave can develop.

 HS3 data will be used to analyse the non genesis event associated with NHC invest AL90 from 2014.  A single flight was made to observe this pre-depression on September 5th 2014 by the HS3 field program.  Dropsonde profiles and aerosol layers from the cloud physics lidar will be used in conjunction with gridded data to show a possible cause for the non-genesis of an otherwise favourable system.  This case will be contrasted with a developing case to show the differences in the interaction of environment and AEW trough and the relationship to TC genesis.