The Impact of Cyclone Hamish on One Tree Island – information from in-situ sensor data Scott Bainbridge, Damian Eggeling, Gavin Feather Australian Institute of Marine Science Track of Cyclone Hamish 6th March, 4am 7th March, 4am 8th March, 4am 9th March, 4am 10th March, 4am NOAA Satellite Image – 9th March 2009 Wind Speed Categories Wind KPH Knots M/Sec Category Gale Force >62 >33 >17 Destructive >89 >48 >25 Cyclonic >117 >63 >32 Source: BoM web site Cyclone Map for 9th March 2009 One Tree Island Source: BoM web site Cyclone report 4pm 9th March A Cyclone WARNING remains current for coastal and island communities from Yeppoon to Hervey Bay. A Cyclone WATCH remains current for coastal and island communities from Hervey Bay to Tewantin. Severe Tropical Cyclone Hamish, a CATEGORY 4 CYCLONE, is located off the Capricornia coast and at 4:00 pm EST was estimated to be 255 kilometres east of Yeppoon and 245 kilometres north northeast of Bundaberg, moving southeast at 17 kilometres per hour. Severe Tropical Cyclone Hamish poses a threat to exposed coastal and island communities between Yeppoon and Hervey Bay [including Heron, Fraser and Lady Elliot Islands]. The cyclone is expected to maintain a southeast track parallel to the coast during the next 24 hours. In the 24 to 48 hour period the cyclone is expected to become slow moving and weaken slightly. Details of Severe Tropical Cyclone Hamish at 4:00 pm EST: .Centre located near...... 22.8 degrees South 153.2 degrees East .Location accuracy........ within 28 kilometres .Recent movement.......... towards the southeast at 17 kilometres per hour .Wind gusts near centre... 250 kilometres per hour .Severity category........ 4 .Central pressure......... 945 hectoPascals Source: BoM web site Air Pressure and Wind Speed Minimum pressure and maximum wind at 3.30pm, 9th March 2009 Min pressure, 999 HPa at 3.30pm, 9th March Max Wind Speed 26 m/sec or 50 knots 9th March 2009 Wind Speed goes up as the Pressure drops, Cyclone takes around 13 hours to pass 13 Hours Destructive Winds Gale Force Winds Strong Winds Tides for the 9th of March Cyclone passed during a low tide (0.8m at 3.30pm) but the days before and after had a large tidal range (>3m) Source: Hydrographic Office Air Temperature and Barometric Pressure Cyclone has little direct impact on air temperature Rainfall Only 11mm of rain recorded with the cyclone (Gladstone had 11mm) 6mm, 13th March 9mm, 10th March 2mm, 9th March Wind Direction – 9th March 2009 Wind direction moves slowly from South-East to South over the day Cyclone passes by but not over One Tree (no ‘eye of the cyclone’ effect) Lagoonal Water Temperatures Central Bommie Dramatic drop in lagoonal water temperatures from 29 degrees to 26.5 degrees. Drop occurs two days before the cyclone, mostly likely due to colder oceanic water being forced into the reef lagoon by winds Lagoonal Water Temperatures Sub-Lagoons within One Tree The pattern of change is similar in each of the three sub-lagoons within One-Tree Island. The red line is the deepest lagoonal thermistor in the main lagoon, the blue line is the equivalent sensor in the second lagoon and the green line is the equivalent sensor in third lagoon. Lagoonal Water Mixing, Central Bommie Profile The graph shows the temperature profile for central bommie with the surface thermistor in red, one at 1m depth (blue line) and the bottom at 2.5m depth (green). The results show some stratification before the cyclone but good mixing during and after the cyclone. Lagoonal Water Mixing, Third Lagoon The graph shows the temperature profile for Third Lagoon with the surface thermistor in red, one at 2.5m depth (blue line) and the bottom at 4.75m depth (green). The results show marked stratification before the cyclone but good mixing during and after the cyclone. Note that Third Lagoon site is deeper than the main lagoon. Summary • Cyclone Hamish passed by One-Tree on the 9th of March 2009 as a Category-4 cyclone • Dramatic drop in barometric pressure around 3.30pm, cyclone ‘eye’ would have been around 130 km away • Minimum recorded pressure was 998.75 HPa • Maximum wind was 26 M/Sec or 50 knots (destructive winds) • Cyclone took around 13 hours to pass by • Minimal rain (2mm on the 9th, 9mm on the 10th) • No immediate impact on air temperature, but… • Water temperatures cooled by 3-4 degrees due to inflow of oceanic water and the lagoon became well mixed • Atmospheric conditions returned to ‘normal’ within 16 hours Site Details GBROOS Sensor Poles Weather Station on Pole 3 One Tree Island Contact: Mr. Scott Bainbridge: 07 4753 4377 GBROOS is a Geographic Node of the Integrated Marine Observing System (IMOS) project (see: www.imos.org.au) funded under the National Collaborative Infrastructure Strategy (NCRIS) an Australian Federal Government initiative and the Queensland State Government and supported by the Tropical Marine Network (TMN)..