[1] On 5 April 2017, the Australian Bureau of Meteorology began monitoring a developing tropical low located in the northeast Indian Ocean, approximately 710 km (440 mi) east of Christmas Island.

[1] The system had been tracking in a generally westwards direction during the previous few days as a weak area of low pressure, but had not been significant enough to warrant the issuance of tropical cyclone warnings.

[9] Aided by favourable environmental conditions, including sea surface temperatures of 29–30 °C (84–86 °F), the cyclone maintained its Category 5 intensity for more than 12 hours, while still tracking to the south-southwest.

[2][3] Soon afterwards, the system turned to the west-southwest and encountered an unfavorable environment of increased wind shear, dryer air, and cooler sea surface temperatures,[1][4] which caused Ernie to weaken.

The renewed period of strengthening proved short-lived and meager, however, as Ernie began weakening again on the afternoon of the same day, before it could reattain Category 4 status.

[4] Soon, in defiance of even this raised intensity forecast, environmental conditions became near perfect for Ernie to intensify extremely rapidly, and to a high degree.

[1] Consequently, Ernie did not cause any known impacts on land in terms of property damage, heavy rain or strong winds and was not retired from the list of names used by the BOM.