During late April and early May, a strong pulse of the Madden-Julian Oscillation tracked eastwards across the tropical Indian Ocean and the Maritime Continent.
Despite the traditional Australian wet season having concluded at the end of April, the pulse led to the redevelopment of monsoonal conditions to the north of Australia.
Additionally, the presence of the pulse led to environmental conditions which were more favourable for tropical cyclogenesis than normal for the cyclone off-season.
As the pulse continued into the Pacific Ocean, the Australian Bureau of Meteorology (BOM) noted the formation of a weak tropical low embedded within a low-pressure trough on 7 May, located within the northwestern South Pacific cyclone region.
The BOM assigned the system the identifier code 26U.
The tropical low moved slowly towards the southwest while organisation gradually proceeded in a generally favourable environment.
By 00:00 UTC on 8 May, the system was located just to the east of Honiara in the Solomon Islands.
After passing over the Solomon Islands, the developing low assumed a more southerly track under the influence of a mid-level high-pressure ridge located to the east.
Over the following few days, the tropical low skirted the boundary of the Australian cyclone region and South Pacific cyclone region, passing between the two basins three times in total.
By 10 May, disagreement emerged between meteorological agencies regarding the prospect of future development for the system.
The BOM anticipated that further development into a tropical cyclone was very unlikely, citing an atmospheric environment that they expected to be unconducive for maintaining a significant tropical system.
Conversely, the United States' Joint Typhoon Warning Center (JTWC) analysed the environment to be supportive of tropical cyclogenesis overall, and forecast a gradual strengthening to tropical cyclone intensity over the following days, in accordance with numerical weather prediction model solutions.
Aided by warm sea surface temperatures and the favourable outflow provided by an anticyclone in the upper troposphere, deep convection continued to grow over the consolidating low-level circulation centre on 11 May. The storm was upgraded to a Category 1 tropical cyclone on the Australian scale by the BOM at 18:00 UTC on 11 May, while located approximately 1420 km (880 mi) east of Cairns.
Located just within the Australian region at this time, the newly formed cyclone was named Ann by the BOM.
The JTWC indicated that Ann had become equivalent to a tropical storm on the Saffir-Simpson hurricane wind scale at this time.

An eastwards-propagating trough in the upper troposphere began to erode the ridge which had been steering the strengthening system southwards.
A new mid-level ridge to the south began to develop, causing Ann to accelerate west-northwestwards across the Coral Sea towards Queensland.
Environmental conditions remained favourable for development, and the system quickly reached high-end Category 1 intensity at 00:00 UTC on 12 May. Soon afterwards, however, competing environmental influences began to arrest the intensification trend.
The cyclone was maintained at Category 1, although the BOM noted that this assessment may have been conservative, with the possibility that the system may have already reached marginal Category 2 intensity.
Analysis of satellite imagery indicated that easterly vertical wind shear had begun to increase near the system, and that drier air had started to become entrained into the circulation from the southwest.
Ann reached peak intensity at 18:00 UTC on 12 May as a low-end Category 2 tropical cyclone on the Australian scale, generating ten-minute sustained winds of 95 km/h (60 mph) and gusts to 130 km/h (80 mph), with a central barometric pressure of 993 hPa (29.32 inHg).
The JTWC reported that one-minute sustained winds reached an estimated 100 km/h (65 mph) at this time, equivalent to a strong tropical storm on the Saffir-Simpson hurricane wind scale.

Ann began to weaken on 13 May. Good poleward outflow provided by the t
During late April and early May, a strong pulse of the Madden-Julian Oscillation tracked eastwards across the tropical Indian Ocean and the Maritime Continent. Despite the traditional Australian wet season having concluded at the end of April, the pulse led to the redevelopment of monsoonal conditions to the north of Australia. Additionally, the presence of the pulse led to environmental conditions which were more favourable for tropical cyclogenesis than normal for the cyclone off-season. As the pulse continued into the Pacific Ocean, the Australian Bureau of Meteorology (BOM) noted the formation of a weak tropical low embedded within a low-pressure trough on 7 May, located within the northwestern South Pacific cyclone region. The BOM assigned the system the identifier code 26U.
The tropical low moved slowly towards the southwest while organisation gradually proceeded in a generally favourable environment. By 00:00 UTC on 8 May, the system was located just to the east of Honiara in the Solomon Islands. After passing over the Solomon Islands, the developing low assumed a more southerly track under the influence of a mid-level high-pressure ridge located to the east. Over the following few days, the tropical low skirted the boundary of the Australian cyclone region and South Pacific cyclone region, passing between the two basins three times in total. By 10 May, disagreement emerged between meteorological agencies regarding the prospect of future development for the system. The BOM anticipated that further development into a tropical cyclone was very unlikely, citing an atmospheric environment that they expected to be unconducive for maintaining a significant tropical system. Conversely, the United States' Joint Typhoon Warning Center (JTWC) analysed the environment to be supportive of tropical cyclogenesis overall, and forecast a gradual strengthening to tropical cyclone intensity over the following days, in accordance with numerical weather prediction model solutions. Aided by warm sea surface temperatures and the favourable outflow provided by an anticyclone in the upper troposphere, deep convection continued to grow over the consolidating low-level circulation centre on 11 May. The storm was upgraded to a Category 1 tropical cyclone on the Australian scale by the BOM at 18:00 UTC on 11 May, while located approximately 1420 km (880 mi) east of Cairns. Located just within the Australian region at this time, the newly formed cyclone was named Ann by the BOM. The JTWC indicated that Ann had become equivalent to a tropical storm on the Saffir-Simpson hurricane wind scale at this time.
An eastwards-propagating trough in the upper troposphere began to erode the ridge which had been steering the strengthening system southwards. A new mid-level ridge to the south began to develop, causing Ann to accelerate west-northwestwards across the Coral Sea towards Queensland. Environmental conditions remained favourable for development, and the system quickly reached high-end Category 1 intensity at 00:00 UTC on 12 May. Soon afterwards, however, competing environmental influences began to arrest the intensification trend. The cyclone was maintained at Category 1, although the BOM noted that this assessment may have been conservative, with the possibility that the system may have already reached marginal Category 2 intensity. Analysis of satellite imagery indicated that easterly vertical wind shear had begun to increase near the system, and that drier air had started to become entrained into the circulation from the southwest. Ann reached peak intensity at 18:00 UTC on 12 May as a low-end Category 2 tropical cyclone on the Australian scale, generating ten-minute sustained winds of 95 km/h (60 mph) and gusts to 130 km/h (80 mph), with a central barometric pressure of 993 hPa (29.32 inHg). The JTWC reported that one-minute sustained winds reached an estimated 100 km/h (65 mph) at this time, equivalent to a strong tropical storm on the Saffir-Simpson hurricane wind scale.
Ann began to weaken on 13 May. Good poleward outflow provided by the t
Cyclone Ann