Tropical Cyclone Yasi roared inland over Queensland, Australia at 12:30am local time on Thursday as a strengthening Category 4 storm with 155 mph winds and a 930 mb central pressure. The cyclone missed the most populous cities on the coast, Cairns and Townsville, which experienced wind gusts to about 60 mph. Undoubtedly, tremendous wind damage occurred in the small towns of Tully, Mission Beach, and Bingal Bay where the eye passed. A storm surge of 5 meters (16 feet) was observed at Cardwell, and 3 meters (10 feet) at Clump Point. Townsville received a 2.5 meter storm surge that damaged some sea walls. This was the highest storm surge observed since 1971 there.


Figure 2. Pressure readings from Clump Point on the Queensland, Australia coast during passage of Yasi bottomed out at 930 mb as the storm passed overhead. Image credit: Australian Bureau of Meteorology.

According to an email I received from Blair Trewin of the Australian Bureau of Meteorology, "Yasi is almost certainly the most intense landfall in Queensland since at least 1918, and possibly since 1899. In 1918 there were two cyclones (at Mackay and Innisfail) with measured pressures in the upper 920s/low 930s but it is quite plausible that the minimum central pressures were lower than that. The 1899 (Mahina/Bathurst Bay) cyclone had a measured pressure (ship near shore) of 914 mb." However, the number of major tropical cyclones along the Queensland coast has declined since the 1870s, according to recent paper by Callaghan and Power (2010). They found that "the number of severe TCs making land-fall over eastern Australia declined from about 0.45 TCs/year in the early 1870s to about 0.17 TCs/year in recent times-a 62% decline. This decline can be partially explained by a weakening of the Walker Circulation, and a natural shift towards a more El Ni�o-dominated era. The extent to which global warming might be also be partially responsible for the decline in land-falls-if it is at all-is unknown."

References
Callaghan, J. and S. Power, (2010): Variability and decline in the number of severe tropical cyclones making land-fall over eastern Australia since the late nineteenth century, Climate Dynamics. DOI: 10.1007/s00382-010-0883-2


Figure 3. Tropical Cyclone Yasi at 03:35 UTC February 2, 2011, as seen by NASA's Aqua satellite.

Jeff Masters

Tropical Cyclone Yasi the second most damaging storm in Australia's history
Tropical Cyclone Yasi has dissipated, but the damage totals from the storm make it Australia's second most expensive tropical cyclone of all-time, according to Tropical Storm Risk, Inc. The storm's $3.5 billion price tag is second only to Cyclone Tracy, which hit Darwin on Christmas Day 1974, doing $3.6 billion in damage (2011 dollars.) Yasi roared inland over Queensland, Australia at 12:30am local time on Thursday as a strengthening Category 4 storm with 155 mph winds and a 930 mb central pressure. The cyclone missed the most populous cities on the coast, Cairns and Townsville, but damaged up to 90% of the buildings in the small towns near where the eye passed--Tully, Mission Beach, and Cardwell. A storm surge of 5.4 meters (17.7 feet) was observed at Cardwell, and there was substantial surge damage at the coast. Fortunately, the storm surge hit near low tide, resulting in a storm tide--the height of the water above land--of about 4.5 meters, more than 2 meters below what would have occurred had Yasi hit at high tide. Yasi moved quickly enough across Queensland after landfall so that major flooding was limited to just three locations near the coast. Yasi's central pressure of 930 mb at landfall made the storm the most intense recorded in Queensland since at least 1918, and possibly since 1899. In 1918, there were two cyclones (at Mackay and Innisfail) with measured pressures in the upper 920s/low 930s, but it is quite plausible that the minimum central pressures were lower than that. The 1899 (Mahina/Bathurst Bay) cyclone had a measured pressure (ship near shore) of 914 mb.


Figure 3. The tide gauge at Carwell, Australia during passage of Tropical Cyclone Yasi recorded a 5.4 meter (17.7') storm surge (red line). Since the surge came near low tide, the storm tide--the height of the surge above mean water--was only 4.5 meters (blue line). The storm tide would have been more than 2 meters higher had Yasi hit at high tide, and the damage from coastal flooding would have been huge. The green line shows the expected water levels at Cardwell due to the tide. Image credit: Queensland government.


Figure 4. Tropical Cyclone Yasi at 04:15 UTC February 3, 2011, as seen by NASA's Aqua satellite.

Jeff Masters