Microwave warm core of Tropical Cyclone Mekunu

By Sreerekha Thonipparambil (EUMETSAT)

Tropical cyclone Mekunu developed as a low pressure over North Indian Ocean on 21 May 2018, reached its peak intensity on 25 May, before making a landfall near Salalah, Oman on the 26 May.

Mekunu had one-minute sustained winds estimated at 115mph and produced about 280mm rainfall in 24 hours — more than three times the annual rainfall average in the region. The storm and the resulting flooding caused destruction including casualties in Oman and Yemen.

The capability of satellite microwave observations to measure the warm core of tropical cyclones is presented in this case study. Unlike visible and infrared channels, channels of microwave sounding instruments like AMSU, onboard Metop and NOAA satellites, can be used to analyse the vertical structure of warm core.

For Mekunu, this is demonstrated in the warm brightness temperature anomalies in Channels 7 (54.94GHz) and 8 (55.54GHz) of AMSU. These channels peak at altitudes which are not affected by clouds, around 200hPa and 100hPa respectively. The warm brightness temperature anomalies increase as the cyclone intensifies. The series of images below depicts this behaviour as the storm develops, intensifies and dissipates. Images courtesy of the CIMSS Tropical Cyclones website .

For very strong storms the warm anomalies can be seen in channels 6 (54.4GHz) and 5 (53.596GHz) too (peaking at around 350hPa and 550hPa, respectively). The direct correlation of AMSU brightness temperature anomalies with both wind speed and minimum sea level pressure can be used to estimate the intensity of the tropical cyclone.

Channel 8

Channel 7

Channel 6

AMSU-A Brightness Temperature Anomaly

Additional content

Cyclone Mekunu in the northwest Indian Ocean (CIMSS Blog)
Cyclone Mekunu kills eleven and leaves dozens missing (The National)