Abstract
Development of a tropical cyclone (TC) requires the alignment of many favorable environmental conditions, but most importantly, requires the presence of a pre-existing disturbance. In the tropical Atlantic, it is widely understood that a large majority of developed TCs form from African Easterly Waves (AEWs) as their pre-existing disturbance. These disturbances can lead to the development of many TCs if environmental conditions allow. This analysis seeks to better understand the portion of Eastern Pacific TCs that have African origins, like their Atlantic counterparts. National Hurricane Center (NHC) Tropical Cyclone Reports (TCRs) attribute all but two cyclogenesis cases in the EPAC to AEWs in 1998, but recent literature has concluded this may not be the case and as many as 2/3 of AEWs could potentially have been mislabeled to the wrong AEW, or not be an AEW at all. Climate Forecast System Reanalysis (CFSR) data was used in conjunction with NHC wave diagnostics to confirm the validity of this recent study. It was discovered that Blas, Isis, and Madeline - which NHC labeled as AEW TCs - could not be traced in potential vorticity (PV) fields further East than the Caribbean. This suggests that 27% of AEW TCs could potentially be mislabeled, and only 62% of total EPAC TCs in 1998 developed from AEWs, rather than 85% like the TCRs suggest. This does not necessarily confirm that these storms were definitively not AEWs, but they were simply not traceable in 310K or 315K PV in CFSR data. This would corroborate some findings from Kerns et al. (2008) which suggested a smaller fraction of TCs than originally thought were indeed AEWs.