Basic Kinematics in Developing and Non-developing Tropical Disturbances Based Upon Dropwindsonde Data During PREDICT

Analyses of wind data gathered from airborne dropwindsondes released from the upper troposphere during the Pre-Depression Investigation of Cloud Systems in the Tropics (PREDICT) experiment are presented. The main focus is on two developing systems that finally became Hurricane Karl and Tropical Storm Matthew and one system that had previously attained Tropical Storm status (Gaston), but subsequently weakened and never redeveloped during five days of monitoring. Relative circulation, average vorticity, and average tangential wind for an enclosing circuit using wind data from the outermost dropwindsondes encircling the wave-pouch region are calculated for each flight at twelve levels between 950 and 200 hPa. Corresponding geostationary satellite imagery correlate these kinematic calculations with convective activity, and co-moving model analyses are used to determine the relation of the winds with the pouch sweet spot.

Although developing pre-Karl temporarily weakened at mid-levels during the first three flights, the circulation remained strong below 850 hPa. Three days later, pre-Karl had strengthened at all levels. Meanwhile, developing pre-Matthew exhibits the strongest circulation at about 800 hPa for the first two flights. The average tangential wind gradually increases throughout the three days, with cyclonic winds throughout the relatively deep 600-900 hPa layer by the third day. Interestingly, the low-level (below 850 hPa) tangential wind for non-developing ex-Gaston is nearly as strong as the two developing systems. However, the cyclonic portion of ex-Gaston clearly diminishes from a circulation that extended up to 300 hPa on the first day of examination to only 700 hPa by the fifth day.

Analyses of divergence/convergence, vertical wind shear, and the vertical alignment of the wave-pouch will be presented also.