While radiosonde observation onboard the Mirai has been started since August 5, enhanced radiosonde soundings (from 12-hourly to 6-hourly) at Palau and Yap have also been started since August 6. In addition, it is expected to have another enhancement at PAGASA Legaspi site, Philippines soon.
Thank you, Palau Weather Service, Yap Weather Service, US/NOAA, and PAGASA for your great help and contributions!
According to the ECMWF report of geographical coverage of observations used for their data assimilation system, those enhanced sounding data have been successfully used by them! We can confirm three red dots in the tropical western Pacific, which were not appeared on the chart as of August 4.
Acknowledgment. Those figures are taken from ECMWF website at https://www.ecmwf.int/en/forecasts/charts/monitoring/dcover