Cyclone Hamish - Meteorological History

Meteorological History

Severe Tropical Cyclone Hamish was first identified on 4 March 2009 by the Bureau of Meteorology (BoM) as a tropical low over the Coral Sea. Drifting westward, the system steadily became better defined, developing convective banding features later that day. Situated in an area favouring tropical cyclone development, characterised by warm waters, low wind shear and upper-level diffluence, the low was able to quickly strengthen. The following day, the Joint Typhoon Warning Center (JTWC) issued a Tropical Cyclone Formation Alert as convection wrapped around the centre of circulation and an anticyclone developed over the system, allowing for good outflow. Hours later, the BoM classified the low as Tropical Cyclone Hamish as the storm began to moved southward in response to a mid-level ridge situated to the east. Shortly thereafter, the JTWC also began monitoring Hamish as a tropical storm.

Not long after being classified a tropical cyclone, Hamish began to undergo rapid intensification, quickly becoming a severe tropical cyclone, a storm with winds exceeding 120 km/h (75 mph), on 6 March. Deep convection continued to develop around a well-defined low pressure centre, allowing for further strengthening. Additionally, satellite images depicted that an eye had begun developing within the storm. A steady south-easterly track was fully established by this time as the ridge to the east and a trough over central Australia prevented westward movement. Based on radar observations, the eye of Hamish was about 28 km (17 mi) in diameter by 7 March. Later that day, the storm further intensified into a Category 5 cyclone on the Australian intensity scale, becoming the first to do so since Cyclone George in 2007. Later that day, Hamish attained its peak intensity with winds of 215 km/h (130 mph) along with a barometric pressure of 924 mbar (hPa; 27.29 inHg). At the same time, the JTWC assessed the storm to have nearly become a Category 5 equivalent on the Saffir–Simpson Hurricane Scale; peak one-minute sustained winds were estimated at 250 km/h (155 mph).

At its peak, Hamish was a small cyclone; gale-force winds covered an area roughly 440 km (270 mi) wide and the radius of outermost closed isobar was about 260 km (160 mi). After maintaining Category 5 status for roughly 24 hours, Hamish began to weaken as the interaction with coastal Australia and increased wind shear took their toll. Late on 8 March, an eyewall replacement cycle had begun to take shape, allowing the storm to maintain Category 4 intensity for the following few days. By 10 March, the storm finally began to show signs of steady weakening as shear continued to increase due to an approaching trough from the west. Later that day, the storm began to slow as it moved within a region of light steering currents. Substantial loss of convection took place during this time, causing Hamish to weaken below severe tropical cyclone status by 11 March.

Convection failed to redevelop over the centre of Hamish throughout 11 March, prompting the JTWC to issue their final advisory on the system. The BoM also declared Hamish a remnant low around the same time; however, they continued to monitor the remnant system as it began to turn towards the northwest due to a ridge south of the storm. The remnants of Hamish tracked in an erratic, north-westward direction over the following few days, backtracking over where it had been days earlier. The system finally dissipated on 14 March off the coast of Australia, never having made landfall.