Severe tropical cyclone Debbie will be remembered as a large and destructive
cyclone. And as with all significant cyclones, the name Debbie will be retired
from the list of Australian cyclone names. So now let's take a look back at
the path and weather of severe tropical cyclone Debbie. The tropical low that
eventually intensified into severe tropical cyclone Debbie developed on
March 22 in the northern Coral Sea, and the environment here was favorable for
the low to intensify into a cyclone because sea surface temperatures were
around 30 °C, giving lots of energy to the system; and because there was a
low vertical wind shear, meaning that there were no dramatic changes in wind
speed with height that would act to tear the system apart. Over the next few days,
as the system developed, it drifted south and it was named tropical cyclone Debbie
at 10 am on Saturday 25 March. And those favorable atmospheric
conditions meant that by 10 pm on the 25th it had reached Category 2
strength, at which point it took a turn towards the coast. Over the next 24 h,
the upper atmospheric conditions became less favorable, so development of the
system stalled, but once the conditions became favorable again Debbie rapidly
intensified from Category 2 to severe Category 4 strength during a 12 h
period on Monday 27 March. We can also see from the track that,
at times, the cyclone slowed down and wobbled around in its path.
These short-term fluctuations in speed and movement are common in tropical cyclones
and they make forecasting the timing and location of landfall all the more challenging.
Now as tropical cyclone Debbie moved closer to the coast,
Hamilton Island began experiencing sustained winds of 100 km/h
or greater, and these continued for around 11 h before the cyclone
crossed the coast and 3–4 hours after that. A peak wind gust of
263 km/h was recorded on the morning of Tuesday 28 March—
and that's severe Category 4 cyclone strength, and the highest wind gust
recorded by the Queensland observation network. The center of the eye across the
mainland near Airlie Beach at 12.40 pm on Tuesday the 28th, and shortly after
crossing the system slowed down to around 7 km/h, which meant that places
slightly inland from the coast such as Proserpine
were exposed to the very destructive core of the cyclone—with wind gusts up
to 165 km/h—for many hours. Further inland, roofs were blown off at
Collinsville, where Category 2 strength winds were experienced. Coastal
inundation from storm surges was reported at many locations: a 2.6 m
surge was recorded at Laguna Quays, with reports of significant
inundation to homes at nearby Conway Beach and Wilson Beach. The system
weakened below tropical cyclone strength in the early hours of Wednesday 29 March
and started to move towards the south in the 48 hours to 9 am on
the 29th. Clarke Range recorded 986 mm and in the 24 h to 9 am
on Thursday 30th. Mount Jukes recorded 635 mm. These periods
of heavy rain led to reports of significant flash flooding, and with
several locations in the Fitzroy River basin receiving up to 1000 mm
of rainfall over two days, major flooding of the Fitzroy River resulted, and it
eventually peaked just below 9 m at Rockhampton the following week.
As ex-tropical cyclone Debby tracked south over the Sunshine Coast and Brisbane on
Thursday 30th damaging wind gusts were observed, along with widespread rainfalls
between 150 and 250 mm, resulting in major flooding of
the Logan and Albert rivers. A record major flood level was reached at Beaudesert
on the Logan River. And in the same 24 h to 9 am on Friday 31st, even
heavier falls were recorded in the Gold Coast hinterland,
where Upper Springbrook received 602 mm. We also saw the dramatic
impact of this extraordinary rainfall over the northeast of New South Wales.
The quick deluge saw rapid rises of river levels in much of the Northern Rivers
area, with major flooding of the Tweed, Brunswick, Richmond and Wilsons
river valleys. Lismore and Murwillumbah were heavily impacted and many
areas in the region received more than 500 mm of rain in 24 h.
The flood peak at Lismore was 11.6 m, which is higher than the
levels recorded in the 2001 and 2005 floods, but lower than the
record of 12.15 m in 1974. Our thoughts are with all those affected by
severe tropical cyclone Debbie. We would like to thank the community for taking
heed of the warnings and acknowledge the volunteers, emergency services, local and
State governments for their tireless efforts in helping the community prepare
for and recover from this disaster event.