Tropical Cyclone Larry, 2006
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Tropical Cyclone Larry, 2006 By Mr Jeff Callaghan Retired Senior Severe Weather Forecaster, Bureau of Meteorology, Brisbane Severe Tropical Cyclone Larry crossed the tropical north Queensland coast near Innisfail during the morning of 20 March, 2006. Larry reached Category 5 for a time just Before landfall. As at 30 OctoBer 2006 there were 30,594 insurance claims for a total of 14,000 houses of which 500 were written off. Building costs were estimated at 1.5 billion 2006AUD. Sugar industry losses were around 200millionAUD with total crop losses exceeding 0.5 Billion 2006AUD. The worst town affected Being Silkwood with 99% of the houses damaged. Examples of the extreme wind damage were 4 high voltage transmission towers Blown down along the Palmerston Highway and another north of Babinda. An Australian record wind gust of 293.7km/h was recorded on the eastern slope of Mt Bellenden Ker from a C.S.I.R.O. anemometer. Very large storm surges (debris lines to 5.2m above MSL) were measured in the Bingil Bay area. Fortunately Larry landed at low tide. Figure 1 Larry (left) and Winifred (right) leading up to landfall (isoBars drawn every 2hPa to 972hPa and red circle marks eyewall. Larry and Winifred Larry crossed the coast in much the same location that Winifred did some 20 years earlier. From Bureau of Meteorology (1986) the central pressure of tropical cyclone Winifred at landfall was 957hPa. Larry appears to have had a similar central pressure as it passed over Innisfail as the barograph at the official observation site which experienced the calm eye indicated a mean sea level pressure of 955hPa. From Figure 1 we see that Larry has many more isobars packed in closer to the centre than does Winifred and was oBviously more intense. There are other reports of pressures around 930hPa, particularly near the southern intense rain Band which is discussed Below. These appear to Be associated with short lived small circulations near the edge of the eye of the cyclone and are called meso scale vortices. A paper on the existence of these vortices is Being prepared By Peter Otto of the Bureau of Meteorology in BrisBane. Cyclone Larry, 2006 Data By J. Callaghan 22 SeptemBer 2011 We show Below that from other data that Larry was far more intense than Winifred. Central pressure is often a poor guide to tropical cyclone intensity. In Figure 1 in Courtney and Knaff (2009), the maximum ten- minute mean wind and minimum pressure relationship from reconnaissance-based best track data in the Atlantic Basin Between 1998 and 2007 shows the maximum wind vary from 65knots to 117knots for central pressures around 955hPa. Forest Damage The difference in severity and size Between Larry and Winifred was Borne out By Forest surveys By Turton (2008). In the case of Cyclone Larry, moderate and severe forest damage extended much further north, south and west than that reported for Cyclone Winifred, despite their similar paths across the landscape. However, slight forest damage for Cyclone Larry appeared to Be less extensive than that reported for Cyclone Winifred. Insurance Costs From Lavin 2007 the costs associated with Larry were extremely large. This does not include crop damage which was extreme and the loss of the banana crop affected Australia’s CPI. As at October 2006 there were 30,594 insurance claims lodged involving damage to approximately 14,000 Buildings of which approx. 500 were considered to Be total losses. Costs are estimated by the Building Services Authority Queensland (BSA) at $1.5 billion 2006 dollars. For Winifred there were similar proBlems to Larry but the damage was less widespread. There were 50 homes in total destroyed with the estimated cost in 2006 dollars $425 million. Size of Larry at landfall Below in Figure 2 we compare Larry with two midgets (Ada and Tracy) and the very large circulation of tropical cyclone David. Ada is By far the tiniest and Larry is a little larger than Tracy and Larry had a larger eye as viewed from radar. The radar eye of Larry was around 30km in diameter as it neared the coast. The diameter of the radar eye of Ada contracted to 18km while the radar eye of Tracy at landfall was elliptical with a major axis of 12km and a minor axis of 8km. The concept of ‘midget’ tropical cyclones originated at the Joint Typhoon Warning Centre in the days of Chip Guard. The definition of a midget is when the radius of gales is 111km or less. Larry thus qualifies to Be called a midget. From Callaghan and Smith (1998) midgets have a much higher central pressure (in the order of 20hPa) for a given intensity compared with a large cyclone. Figure 2 Comparison of the structure of Larry with David, Ada and Tracy and all drawn to a similar scale. Cyclone Larry, 2006 Data By J. Callaghan 22 SeptemBer 2011 Intensification up to landfall Microwave images of tropical cyclone Larry were oBtained courtesy of the US Navy Research LaBoratory Monterey (California) Satellite Section at http://www.nrlmry.navy.mil/tc_pages/tc_home.html. These are placed in Figure 3, which indicated the increase in convective rain and thunderstorm activity (red areas) around the centre as Larry approaches the coast and makes landfall. Figure 3 Microwave images of Larry from 2118 UTC 17 March to 2234UTC 19 March 2006. Figure 4 Infrared image at 1733UTC 19 March 2006. Cyclone Larry, 2006 Data By J. Callaghan 22 SeptemBer 2011 The enhanced Infrared satellite images (example in Figure 4) of Larry approaching landfall indicated a tropical cyclone near the transition from Australian category four intensity to Australian category five intensity. The Satellite technique to calculate maximum sustained wind speed in a tropical cyclone for infrared imagery is relatively simple for tropical cyclones with an eye. In Figure 7 the sequence shows Larry leading up to landfall and the first four images are all rated T6.5 which signifies that Larry was at the lower end of the Australian Category 5 intensity. In this system the colder the cloud top temperatures surrounding the eye and the warmer the eye temperature, the more intense the system is. The temperature difference is a proxy for the strength of the up motion in the thunderstorms around the eye and the subsidence in the eye and correlates well with cyclone intensity. The red colour is very cold cloud tops (colder than -80degrees Celsius) and was generated by very strong thunderstorm activity around the eye wall and this can be seen to reduce in size near the centre up to 1833UTC 19 March (lower left frame). The dark Blue (-76 to -80 degrees Celsius), light Blue (-70 to -75degrees Celsius) and red areas have all weakened By 1933UTC and the rating drops to T 6.0 which is at the top of the Category 4 scale. Although there is a lag in the fall in intensity and it still would Be rated as a Category 5 system under this technique. At landfall at 2033UTC there is another Burst in thunderstorms which you can see By the red cloud top circulating around the southern and western sides of the eye. This Band of intense convection on the southern side of the eye was associated with the worst wind damage and the largest storm surge. Figure 5 Radar images from Mount Stuart radar near Townsville from 1930UTC to 2100UTC 19 March 2006. The red dot marks the position of Innisfail. In Figure 5 the centre of Larry was located more or less the same distance from the Townsville radar located on Mount Stuart so it is useful for determining signs of intensification. The light Blue and yellow colours signify the heavier convective precipitation and over the period in Figure 5 Larry Cyclone Larry, 2006 Data By J. Callaghan 22 SeptemBer 2011 clearly intensified up to landfall as strong convective rain developed close to the centre around the eye. Notice that the strong southern Band of convection is the same thunderstorm area evident in the infrared imagery in Figure 4. Also there was no strong convection on the western side of the eye at 2000UTC (top right frame) as it approached Innisfail. The southern Band of convection wrapped around the western side of the eye after landfall virtually missing Innisfail. This is important in analysing the oBservations from the official oBserver at Innisfail. Around 5:20 am (1920UTC), the first report received at the Brisbane Tropical Cyclone Warning Centre of intense coastal winds from Larry was via a phone call from a yacht anchored at Mourilyan HarBour. The person on the yacht reported an anemometer measured wind gust of 225 km/h. From Figure 5 these winds occurred when the massive southern convective cloudBand reached the coast. Mourilyan HarBour is located immediately south southeast of Innisfail in Figure 5 where the range- ring crosses the coast. No further oBservations were possiBle, as the mast of the vessel snapped after this report. However 10 minutes later at 5:30 am a citizen at his home in MoresBy (11 km west southwest of Mourilyan) recorded a southeasterly gust of 240km/h on his home weather station before his anemometer also failed. These instruments were unavailable for calibration and we are unable to comment on their accuracy. Figure 6 Radar imagery received from Mount Stuart radar. This was at the time of the very large surge near Clump Point. The worst damage was associated with this southern eye wall. In Figure 6 is a close up of the southern convective Band. The strongest winds should Be found just to the north of the strongest convection (yellowy green Band) and this was where the worst storm surge and wind damage was found.