During its formative stages, the low dropped heavy rain over Fiji, which had already been affected by Cyclone Ami two weeks prior.

On January 25, 2003, a low-pressure area formed within a monsoon trough about 300 mi (485 km) northwest of Fiji and moved to the east-southeast.

Shortly thereafter, Cilla turned southeast hours later in the general direction of Tonga[2] Early on January 26, RSMC Nadi designated the low as Tropical Depression 07F, after attaining 10-minute sustained winds of 35 mph (55 km/h).

[3] At the time, the slow moving system had a poorly defined center of circulation that was hard to identify via radar and satellite imagery.

[2] At 0600 UTC January 28, Cilla reached its peak intensity, with 10–minute sustained winds of 45 mph (70 km/h) per RMSC Nadi.

[7] According to RMSC Nadi, Cilla weakened slightly[2] as the storm lost organization due to increased wind shear.

[2] With the center exposed from the deep convection, Tropical Depression Cilla transitioned into an extratropical cyclone at 1100 UTC the next day, on January 30.

[9] When Cilla first posed a threat to Tonga, the Fiji Meteorological Service (FMS) issued a tropical cyclone alert for the entire island chain.