A study on the intensity change of typhoon Nakri (0208) - observation and GDAPS data analysis

Typhoon Nakri(0208), formed as a Tropical Storm (TS) at about 400km southwest of Taiwan on 1800UTC 8 July, 2002, was studied using two Aerosondes and the GDAPS (Global Data Analysis and Prediction System) analysis data. The evolution of 200-850 hPa vertical wind shear and 200 hPa eddy relative angular momentum flux convergence (EFC) based on the GDAPS analysis data showed that typhoon Nakri has experienced an intensity change since 0000UTC 13 July when the vertical shear exceeds 10 m s-1. It was also found that during the period of interacting with the trough, positive values of EFC was larger than other times. The Aerosonde observations showed that a strong inversion layer and isohume layers exist in the lower tropospheric vertical structures over the ocean ahead of typhoon. Isohume layers are composed of very wet (nearly saturated) below 850 hPa, and dry above 830 hPa during the rapidly weakening period of typhoon. When the northwesterlies were present at altitude between 1.5 km and 3.5 km about 3 hours before the typhoon weakened, the trough at 850 hPa moved southward, which was related to a typhoon-trough interaction. Keywords: Typhoon Nakri, Intensity Change, GDAPS analysis Data, Aerosonde, Typhoon-Trough Interaction.