Tropical Cyclone Donna was an out-of-season cyclone that broke records in May 2017.
By Sancha Lancaster and Jose Prieto (EUMETSAT) and HansPeter Roesli (Switzerland)
Donna started as a disturbance before being officially classed as a Tropical Cyclone by the Joint Typhoon Warning Center (JTWC) on 2 May.
By 06:00 UTC on 3 May it had reached Category 1 on the Australian tropical cyclone scale and was named 'Donna' by the Fiji Meteorological Service (FMS). Figure 1 (top right, click to expand) is the Metop-A AVHRR view of the cyclone over Vanuatu and the Solomon Islands, east of Australia, on 3 May at 23:16 UTC.
Despite some evidence of wind shear along the northern fringes of the storm, it began to clear an eye late on 4 May and on 6 May at 00:00 UTC Donna reached its first peak as a Category 4 cyclone (equivalent to a Category 3 hurricane), see the Himawari-8 band 14 image (Figure 2). Tropical Cyclone Donna's progress can be followed in the Himawari-8 Band 14 (11 µm) animation from 3 May 20:20 UTC–6 May 03:50 UTC (MP4, 4 MB).
By 7 May the cyclone had a solid ring of deep convection surrounding a well-defined 55 km (35 mi) eye.
The FMS upgraded Donna to a Category 5 cyclone (equivalent to a Category 4 hurricane) at 00:00 UTC on 8 May, estimating that the storm possessed 10-minute sustained winds of 205 km/h (127 mph).
View image on Google Earth
As a result, Donna became the strongest off-season tropical cyclone on record during the month of May in the South Pacific basin.
The eye is clearly defined on the Himawari-8 Visible imagery, see Figure 3 and the animation from 3 May 03:00–06:20 UTC (MP4, 4 MB).
Tropical Cyclones Donna and Ninteen (EUMETSAT Flickr)
Cyclone Donna in the South Pacific Ocean (CIMSS Blog)
Tropical Cyclone Donna Impacts New Caledonia After Battering Vanuatu For Days (The Weather Channel)