Airborne radar observations of pre-depression Hagupit during TPARC/TCS-08

The ELDORA airborne Doppler radar was deployed as part of the TPARC/TCS-08 field campaign to study the life-cycle of tropical cyclones in the northwest Pacific basin. Observations collected during two consecutive aircraft missions into pre-depression Hagupit reveal a developing low-level circulation (LLC) three days prior to the Joint Typhoon Warning Center tropical cyclone formation alert. At 00Z 14 September 2008 the tropical disturbance exhibited a classical ‘open-wave' structure at the NRL P3 flight level (~650 hPa). A weak LLC was clearly evident, however, in satellite imagery and dropsonde observations, and has been further confirmed by ELDORA derived winds. The two-plane mission 24 hours later revealed that the LLC was persistent as the disturbance moved into a lower shear environment with increasing convection. Model analyses suggest that the nascent circulation was protected within a "marsupial wave pouch" during this early development period. Hagupit later developed into a supertyphoon causing over 1 billion dollars in damage and 67 deaths. ELDORA radar data was collected in both stratiform and deep convective regions in order to examine the structure and evolution of the pre-depression. Analysis and interpretation of these observations will be presented using a new finite-element based variational technique that can incorporate in situ and dropsonde data into the dual-Doppler synthesis.