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North QLD tropical low may hit coast as Category 4 Cyclone
Updated 25/3/17 18.45EDT: See second story below
A tropical low that has been drifting generally south from New Guinea over the past few days may develop into a severe Tropical Cyclone before hitting the northern QLD coast early next week.
The Bureau of Meteorology's Tropical Cyclone Warning Centre in Brisbane issued its first cyclone advice yesterday afternoon at 17.00. The advice, technical bulletin and track map issued around 05.00EST this morning show an increasing confidence that the cyclone, which will most likely be named Tropical Cyclone Debbie, will form this afternoon and strengthen as high as Category 4 before arriving at the QLD coast on Monday evening or Tuesday morning next week.
The TCWC says the system is now being eyeballed on the Willis Island radar, and surface observations from Lihou Reef, SE of Willis, indicate the pressure at its centre, located 620km ENE of Townsville, has dropped significantly over the past 24 hours to 991.8hPa at 04.00EST. Steering the overall movement of the cyclone will be the middle atmosphere windflows which are currently moving it SSE, but are expected to swing it onto a west to WSW track today, which will then continue all the way to the QLD coast.
Adding to a heightened sense of preparedness in northern QLD is that the system is, and will continue to be, in an "environment [that] will remain supportive of intensification right up to landfall on the Queensland coast" says the TCWC. The 04.51EST track map and statements from the BoM suggest it could strengthen as high as Category 4 before landfall.
Although all the models available to the Bureau are indicating a similar W to WSW track into the QLD coast, Tropical Cyclones are notoriously unpredictable as they perform track wobbles within the broader steering environment. However, forecasters produce a cone-shaped area of likely tracks ahead of the advancing cyclone, and that will narrow down to a likely landfall area as the cyclone nears the coast. As at 05.00, the TCWC had the Watch Zone extending along 800km of the north QLD coast from Cape Tribulation down to St Lawrence, but this will narrow as certainty increases.
Should the cyclone arrive at the coast as a Category 4, the second-highest level, it should not be underestimated. The BoM describes a Category 4 cyclone impacts as "Significant roofing loss and structural damage. Many caravans destroyed and blown away. Dangerous airborne debris. Widespread power failures. [The] strongest winds are VERY DESTRUCTIVE winds with typical gusts over open flat land of 225 - 279 km/h." In addition, the TCWC expects heavy rain, flooding and abnormally high tides. As with the cyclone's track, its intensity at landfall is also difficult to predict.
To keep fully up to date, use the TCWC Current Tropical Cyclones page to access all available warnings, track maps, technical information and backgrounder advice in the one place. Updates are currently being issued every six hours around 05.00, 11.00, 17.00 and 23.00, but the frequency of updates would increase as the cyclone intensifies and gets closer to land.
Tropical Cyclone Debbie to head for QLD coast - afternoon update
Tropical Cyclone Debbie was declared just before 11.00 EST. The system has become much more organised during the morning as began turning to the SW, and a clear, though not circular, eye developed around noon.
The forecast track has moved progressively south in the forecasts issued since this morning's story, and the Forecast Track Map issued at 17.09EST this afternoon shows it crossing the coast near Ayr, 70km SE of Townsville. Consequently, watch and warning zones have been shifted south. The Watch Zone (gales expected from 24 to 48 hours) is from Cairns to Ayr and the newly-declared Warning Zone (gales expected within 24 hours) is from Ayr to St Lawrence.
TC Debbie, now at Category 1, has been relatively slow moving today but is expected to move steadily WSW this evening and continue moving WSW as it increases to Category 4 before landfall. The latest warning says "Tropical Cyclone Debbie is expected to cross the coast between Townsville and Proserpine on Tuesday morning, most likely as a CATEGORY 4 tropical cyclone, with wind gusts up to 260 kilometres per hour near the centre.
"DESTRUCTIVE winds are likely to develop about the Whitsunday Islands and nearby coast on Sunday evening, and extend to other areas between Ayr and Mackay overnight into Monday morning. GALES are expected to develop between Ayr and St Lawrence from late Sunday afternoon and evening, and may extend to other coastal areas north to Innisfail during Monday."
In addition, abnormally high tides with large waves are expected at least between Lucinda and Mackay, while areas of heavy rain are expected, with a Flood Watch current.
The cyclone is becoming impressively large with spiral banding now covering much of the Coral Sea. It has become slowly more organised during the day, its slow central development being fairly typical of very large tropical lows, according to the BoM Brisbane Tropical Cyclone Warning Centre. The Centre says in its Technical Bulletin "Given such a large circulation, it can be expected that the system will have some effect back onto the surrounding steering systems - this is part of the reason for the drift to more southerly tracks recently. All model guidance is in agreement with this scenario, although there remain some differences in forward speed amongst the guidance, which affects not only the time of impact, but also the length of time available for the system to intensify over the water."
The Centre also notes that "the environment will remain supportive of intensification right up to landfall on the Queensland coast."
Keep up to date with latest warnings, track maps and detailed bulletins on the TCWC Current Tropical Cyclones page. The Sydney Morning Herald also gave a good account of the situation late this afternoon, saying "BoM Queensland regional director Bruce Gunn couldn't rule out the possibility of the cyclone becoming a category five, depending on how long it stayed over the ocean, and said there was also the possibility of the system increasing speed and making landfall as early as Sunday night." The less time it spends developing over the Coral Sea, the weaker it will be on landfall.